Several antivirus products from security firm ESET had a critical vulnerability that was easy to exploit and could lead to a full system compromise.
The discovery of the flaw, which has now been patched, comes on the heels of a report that intelligence agencies from the U.K. and the U.S. are reverse engineering antivirus products in search for vulnerabilities and methods to bypass detection.
The vulnerability in ESET products was discovered by Google security engineer Tavis Ormandy and was located in their emulator, the antivirus component responsible for unpacking and executing potentially malicious code inside a safe environment so that it can be scanned.
ESET did not immediately respond to a request for comment.
The ESET products monitor disk input and output operations and when executable code is detected they run it through the emulator to apply the detection signatures.
"Because it's so easy for attackers to trigger emulation of untrusted code, it's critically important that the emulator is robust and isolated," Ormandy said in a blog post. "Unfortunately, analysis of ESET emulation reveals that is not the case and it can be trivially compromised."
The vulnerability found by the Google researcher allows a remote attacker to execute arbitrary commands with the highest system privilege. The flaw is particularly dangerous because it can be exploited in many ways, including by simply loading a website in the browser, downloading an email message in a local email client, plugging a USB thumb drive into the computer and other actions that trigger disk operations.
Because it's so easy to exploit, the flaw can be used to create a computer worm that spreads from one computer to another, including on "air-gapped" networks though USB thumb drives, according to Ormandy.
The vulnerability affects ESET Smart Security for Windows, ESET NOD32 Antivirus for Windows, ESET Cyber Security Pro for OS X, ESET NOD32 For Linux Desktop, ESET Endpoint Security for Windows and OS X and ESET NOD32 Business Edition.
The company released a scanning engine update Monday to fix the flaw, so users should make sure they update their products.
This is not the first time that security researchers have found serious vulnerabilities in antivirus products. In 2012, Ormandy found critical vulnerabilities in Sophos Antivirus and last year he found a flaw that could be exploited to remotely disable the protection engine used in many Microsoft antimalware products.
Also last year, Joxean Koret, a researcher at Coseinc, found dozens of remotely and locally exploitable vulnerabilities in 14 antivirus engines.
Unlike some other software applications, antivirus programs have a very large attack surface because they need to inspect many types of files and code written in different languages from various sources, including the Web and email; and file parsing has historically been a source of many vulnerabilities.
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