This post breaks the two-year silence of this blog, showcasing a selection of memory corruption vulnerabilities in Bitdefender’s anti-virus engine. The goal of binary packing is to compress or obfuscate a binary, usually to save space/bandwidth or to evade malware analysis. A packed binary typically contains a compressed/obfuscated data payload. When the binary is executed, a loader decompresses this payload and then jumps to the actual entry point of the (inner) binary.
As I briefly mentioned in my last two posts about the 7-Zip bugs CVE-2017-17969, CVE-2018-5996, and CVE-2018-10115, the products of at least one antivirus vendor were affected by those bugs. Now that all patches have been rolled out, I can finally make the vendor’s name public: It is F-Secure with all of its Windows-based endpoint protection products (including consumer products such as F-Secure Anti-Virus as well as corporate products such as F-Secure Server Security).
After my previous post on the 7-Zip bugs CVE-2017-17969 and CVE-2018-5996, I continued to spend time on analyzing antivirus software. As it happens, I found a new bug that (as the last two bugs) turned out to affect 7-Zip as well. Since the antivirus vendor has not yet published a patch, I will add the name of the affected product in an update to this post as soon as this happens.
In my previous posts about the two Bitdefender bugs related to 7z, I explicitly mentioned that Igor Pavlov’s 7-Zip reference implementation was not affected. Unfortunately, I cannot do the same for the bugs described in this blog post. I found these bugs in a prominent antivirus product and then realized that 7-Zip itself was affected. As the antivirus vendor has not yet published a patch, I will add the name of the affected product in an update to this post as soon as this happens.
A few days after having published the post about the Bitdefender stack buffer overflow via 7z PPMD, I discovered a new bug in Bitdefender’s product. While this is a 7z bug, too, it has nothing to do with the previous bug or with the PPMD codec. Instead, it concerns dynamic memory management. In contrast to the previous post, which described an arbitrary free vulnerability in F-Secure’s anti-virus product, this post presents the first heap buffer overflow of this blog series.
The previous posts of this blog series have been about stack based buffer overflows. With this post, I want to move on to bugs that involve dynamic memory management. Since there are not that many publicly documented arbitrary free vulnerabilities in prominent software products, I thought it would be worth sharing this one. The Transport Neutral Encapsulation Format (TNEF) is an e-mail attachment format developed by Microsoft. It can be used to represent complicated messages and attachments, consisting of many different files and file types, as a flattened stream.
If you read my previous blog post and were bored by it, then this might be for you. With the second post of the series, I am delivering on the promise of discussing a bug that occurs in a more complex setting. A bug in a software module that extracts a prominent archive format (such as 7z) needs to be treated with great caution. It is often critical not only for the software itself, but also for many different software products that are sharing the same library or are based on the same reference implementation.
If I told you I found a remotely triggerable stack-based buffer overflow in a conventional anti-virus product, in what part of the software would you expect it to be? A reasonable guess may be: “Probably in the parsing code of some complicated and likely obsolete file format”. In fact, the most recent anti-virus stack buffer overflows clearly show that the implementation of a parser for complex file formats is extremely challenging.
In the past couple of years, we have seen quite a few critical security issues concerning anti-virus software. A significant number of bugs has been found by Google’s Project Zero, but there is also a lot of effort from other companies as well as from private researchers. Observing those issues, the following question arises naturally: Does anti-virus software decrease the security of our systems? This is a question that has been discussed for many years now, and for many experts the answer seems to be clear.