Last week, Talos discovered multiple vulnerabilities in 7-Zip, a popular, open source file archiver. The vulnerabilities are particularly severe as many products, including antivirus software, implement 7-Zip in their software. When vulnerabilities are found, it is the responsibility of software owners to patch them. However, these patches are useless, unless users update their software.
Avast is not affected by these vulnerabilities, but if you are a non-Avast user we recommend you update your antivirus software, if you haven’t done so already.
About the vulnerabilities
The two vulnerabilities found are CVE-2016-2335 and CVE-2016-2334. The first vulnerability is an out-of-bounds read vulnerability, which exists due to how 7-Zip handles Universal Disk Format (UDF) files and could allow attackers to remotely execute code.
The second vulnerability is an exploitable heap overflow vulnerability, found in the Archive::NHfs::CHandler::ExtractZlibFile method functionality. In the HFS+ file system, files, depending on their size, can be split into blocks. There is no check to see if the size of the block is bigger than size of the buffer, which can result in a malformed block size which exceeds the buffer size. This will cause a buffer overflow and heap corruption.
What you should do
As mentioned above, it is up to software publishers to provide their users with vulnerability fixes, but these are futile if users don’t take action and update their software. It is vital that you frequently update all software, including your operating system, on a regular basis.