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BitDefender protects its users against zero day flaw in Internet Explorer 6 and 7

March 2010 by Bitdefender

BitDefender® has released an emergency update to protect computer users against the newly-discovered flaw in Internet Explorer® versions 6 and 7 which could allow remote code execution, after tricking the user into visiting a malicious web page. Microsoft has issued a warning bulletin and a patch is underway to mitigate the vulnerability.

In order to stay safe, BitDefender recommends that you download, install and update a complete antimalware suite with antivirus, antispam, antiphishing and firewall protection and take extra caution when prompted to open files from unfamiliar locations.

Potential risk scenario

Initially, a prospective victim is lured into visiting a specially crafted web link advertised either via spam messages or as posted on bulletin boards, social networks etc. This webpage contains JavaScript code obfuscated by using the escape function. In order to bypass detection from antivirus products, the script calls a secondary JavaScript that replaces a variable with the unescape string.

The decrypted result is actually the malicious payload which will trigger a heap spray attack and will write the malicious code into the browser’s User Data area, making it persistent. Every time the browser starts, the malicious code is executed without any subsequent intervention (drive-by download), which will result in the automatic download of a file called either notes.exe or svohost.exe (detected by BitDefender as Gen:Trojan.Heur.PT.cqW@aeUw@pbb).

Mitigating the risks

Microsoft has announced that the exploit is already in the wild and that users will be provided with a fix ‘as soon as possible.’ Since Internet Explorer® 8 is not vulnerable to the attack, the next logical step would be to upgrade immediately. However, many custom-made applications in the corporate environment are strongly interconnected with IE 6 or IE 7 and might not work as expected on Internet Explorer 8.

BitDefender is currently detecting the exploit and blocking the malicious code before it is able to inflict any damage to a user’s computer. Moreover, all BitDefender customers have been proactively protected against the infected binaries which the exploit is trying to install on the local machine.

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