Google on Friday took the unusual step of issuing a security warning to users of Microsoft Internet Explorer. The company said that it has seen a significant number of targeted and apparently politically-motivated attacks directed at those accessing services at Google and at an unspecified popular social networking through Internet Explorer.
"We believe activists may have been a specific target," Google's security team said in a blog post.
Google declined to elaborate on which activists have been targeted or where the attacks have been coming from.
Early last year, Google reported that it had been targeted by a sophisticated cyber attack from China and that the Gmail accounts of human rights activists had been a secondary target. The Gmail accounts of Vietnamese activists were also targeted last year.
The recent attacks attempt to utilize an MHTML flaw affecting all versions of Windows that Microsoft acknowledged in January.
MHTML is a container format that combines several documents into a single file using MIME encapsulation. The way MHTML is parsed is insufficiently robust, according to Google security research Michael Zalewski. This allows an attacker to use MHTML files to conduct server-side cross-site scripting attacks (XSS).
Zalewski says the vulnerability appears to have been around since 2004 and has been independently rediscovered several times since. "In 2006, the vendor [Microsoft] reportedly acknowledged the behavior as 'by design'; but in 2007, partial mitigations against the attack were rolled out as a part of MS07-034 (CVE-2007-2225)," he wrote in a blog post. "Unfortunately, these mitigations did not extend to a slightly modified attack published in the January 2011 post to the full-disclosure@ mailing list."
Google's security team sees attempts to exploit this vulnerability as noteworthy because the attacks show a high level of sophistication. "To date, similar attacks focused on directly compromising users' systems, as opposed to leveraging vulnerabilities to interact with Web services," the researchers wrote.
Google's security team says they're working with Microsoft to develop a permanent fix. Until then, Zalewski and Microsoft are recommending that vulnerable users run a Microsoft Fix It script as a workaround.