Flaw in F-Secure Products Allowed Code Execution via Malicious Archives

A critical vulnerability affecting many consumer and corporate products from F-Secure could have been exploited for remote code execution using specially crafted archive files.

A researcher who uses the online moniker “landave” has identified several vulnerabilities related to 7-Zip, an open source file archiver used by many commercial products. Some of the security holes impact 7-Zip and products using it, while others are specific to the third-party implementations of 7-Zip.

Some of the vulnerabilities, disclosed in 2017, impact Bitdefender products (Bitdefender released patches in August 2017). On Tuesday, landave published a blog post describing how one of the 7-Zip bugs he identified last year, namely CVE-2018-10115, can be used to achieve remote code execution on most F-Secure endpoint protection products for Windows.

The details of the vulnerability have been disclosed after F-Secure rolled out a patch via its automatic update mechanisms on May 22. Users don’t need to take any action, unless they explicitly disabled automatic updates.

The list of impacted products includes F-Secure SAFE for Windows, Client Security, Client Security Premium, Server Security, Server Security Premium, PSB Server Security, Email and Server Security, Email and Server Security Premium, PSB Email and Server Security, PSB Workstation Security, Computer Protection, and Computer Protection Premium.

Exploiting the vulnerability against 7-Zip directly was relatively easy and it only required the targeted user to extract a specially crafted RAR file. However, in the case of F-Secure products, exploitation is more difficult due to the use of the Address Space Layout Randomisation (ASLR) memory protection system.

However, landave has found a way to bypass the protection and achieve code execution via malicious RAR files. The attacker could have sent the malicious file to the victim attached to an email, but this attack scenario required that the recipient manually trigger a scan of the file.

A more efficient method involved getting the victim to visit a malicious web page set up to automatically download the exploit file.

“It turns out that F-Secure’s products intercept HTTP traffic and automatically scan files with up to 5MB in size. This automatic scan includes (by default) the extraction of compressed files. Hence, we can deliver our victim a web page that automatically downloads the exploit file. To do this silently (preventing the user even from noticing that a download is triggered), we can issue an asynchronous HTTP request,” the researcher explained.

In its own advisory, F-Secure said the flaw could have been exploited to take complete control of a system, but there was no evidence of exploitation before the release of the patch.

The security firm also pointed out that some user interaction was required for the exploit to work and noted that archive scanning is only triggered if the “Scan inside compressed files” option is enabled.

F-Secure has paid out a bug bounty, but the amount has not been disclosed. According to its Vulnerability Rewards Program page, the company offers up to €5,000 ($5,800) for vulnerabilities that allow remote code execution on the client software.

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