Flawed 7-Zip compression tool opens systems to hack.Update it now!

Pierluigi Paganini May 12, 2016

Recently security experts at Cisco Talos have discovered multiple exploitable vulnerabilities in 7-Zip that open users to cyber attacks.

According to the Cisco security researcher Jaeson Schultz, multiple flaws in the 7-Zip compression tool could be exploited by hackers to gain the complete control on the target machine running the popular software.

“Recently Cisco Talos has discovered multiple exploitable vulnerabilities in 7-Zip. These type of vulnerabilities are especially concerning since vendors may not be aware they are using the affected libraries.” states a blog post published by CISCO Talos.  

The first issue discovered by the expert is an out-of-bounds read vulnerability (CVE-2016-2335)” that exists in the way 7-Zip handles Universal Disk Format (UDF) files.

“An out-of-bounds read vulnerability exists in the way 7-Zip handles Universal Disk Format files. This vulnerability can be triggered by any entry that contains a malformed Long Allocation Descriptor,” states Talos.

7-Zip flaws

The experts at CISCO discovered also a second heap overflow vulnerability (CVE-2016-2334) that exists in the Archive::NHfs::CHandler::ExtractZlibFile method functionality of 7-Zip.

The expert reported the security issues to the  maintainers of the open source 7-Zip platform that promptly worked to a patch. Schultz explained that attackers could exploit the flaw to compromise updated machines and get the same access rights as the logged-in users.

“Anytime the vulnerable code is being run by any sort of privileged account, an attacker can exploit the vulnerability and execute code under those same permissions,” explained Schultz. “A fully patched Windows 10 box lacking the 7-Zip fixes would not help you.” continues the post. “An exploitable heap overflow vulnerability exists in the Archive::NHfs::CHandler::ExtractZlibFilemethod functionality of 7-Zip.” “There is no check whether the size of the block is bigger than size of the buffer buf, which can result in a malformed block size which exceeds the mentioned buf size. This will cause a buffer overflow and subsequent heap corruption.” 

The issues are caused by the failure of input validation process, but the most worrisome aspect of the story is that several software solutions rely on the 7-Zip compression tool. By simply querying Google for the 7-Zip licence (http://7-zip.org/license.txt) it is possible to retrieve a long list of solutions that use it.

“This can be of particular concern, for example, when it comes to security devices or antivirus products. 7-Zip is supported on all major platforms, and is one of the most popular archive utilities in-use today. Users may be surprised to discover just how many products and appliances are affected.” 

Users are urged to update their 7-Zip software to the latest version 16.00.

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Pierluigi Paganini

(Security Affairs – 7-Zip, hacking)

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