New Critical IE Vulnerability Spotted in the Wild

Users running Internet Explorer versions 6 and 7 can get infected by simply visiting a specially crafted web page that uses highly obfuscated JavaScript code to create a use-after-free error, such as a pointer being accessed after the deletion of an object.

Anatomy of the attack

Initially, the user is lured into visiting a specially crafted web link advertised either via spam messages or as posted on bulletin boards, social networks etc. The respective webpage contains JavaScript code obfuscated using the escape function. In order to bypass detection from various 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).

This approach is similar to the one described in CVE-2010-0249 that has been used in targeted attacks against 34 major corporations including Google^TM and Adobe^TM.

Mitigating the risks

 Microsoft announced that the exploit is already in the wild and that users will be provided with a fix as soon as possible. Most likely, the vendor will issue a patch on the next "patch Tuesday", namely on April 13. 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 inflicting any damage to the computer. Moreover, all BitDefender customers have been proactively protected against the infected binaries the exploit is trying to install on the local machine.

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 to manifest extra caution when prompted to open files from unfamiliar locations.