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MHTML security for Internet Explorer: Worth disabling MHTML IE?

Threats expert Nick Lewis discusses a recent vulnerability in MHTML security, and whether disabling the MHTML IE function is the best defense tactic.

Considering recent MHTML exploits that have surfaced for Internet Explorer, would you recommend disabling MHTML within IE? Could doing so have other deleterious effects on security or browser functionality?

The MHTML exploit is similar to past exploits in the Windows Graphics Rendering Engine and is the most recent in a long line of exploits for Internet Explorer involving MHTML, including a vulnerability in MHTML from 2006.  The current MHTML exploit allows an attacker to access data on the system or to install malicious code; it could be included in a browser exploit pack or with other malware. 

Microsoft describes the vulnerability on its Security Research and Defense blog where Microsoft states that Windows XP and newer are vulnerable.

Before disabling MHTML IE, evaluate your organization's risk tolerance and security needs. However, except for organizations with high-security environments where IE is in use, it's probably best to wait for a patch from Microsoft, since at this point, there is no mass worm or virus that exploits the MHTML security vulnerability.

Of note: There is a Microsoft FixIt available that locks down the MHTML protocol that is similar to the way other protocol handlers have been locked down. The FixIt will mitigate this specific issue and can be used if your organization is under attack as a result of this vulnerability; the FixIt should have minimal impact on functionality.  Once a patch is released, however, you may need to re-evaluate whether the FixIt should be removed and the systems restored to the previous settings.

This was last published in August 2011

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