MS06-042 Related Internet Explorer 'Crash' is Exploitable

Date:
August 22, 2006

Severity:
Critical

Systems Affected:
Windows 2000 with IE6 SP1 and MS06-042 hotfix installed
Windows XP SP1 with IE6 SP1 and MS06-042 hotfix installed

Source: eeye.com

Overview:
On August 8th Microsoft released MS06-042 which was a
cumulative update for Internet Explorer. Over the course of a few days after the release of this patch various Internet Explorer users and businesses started to experience Internet Explorer crashing problems when viewing certain websites.

Later on August 11th Microsoft created a knowledge base article which talked about problems with the MS06-042 patch and how Internet Explorer could crash when viewing some web pages that used compression. This Microsoft KB article referenced a patch, which could be requested through Microsoft Product Support Services, that would fix the "crashing" bug. There was further discussion about the extent of the crashes and widespread nature of the bug on places such as SANS and various patch and IT mailing lists. Because of the widespread discussions and number of people experiencing the Internet Explorer crash various security researchers, including eEye, decided to investigate as a lot of times crashes can be exploitable.

We have since found that indeed the reason that people are experiencing Internet Explorer browser crashes is certain websites, that use HTTP 1.1 compression (as stated by Microsoft ), are causing a non-malicious buffer overflow to occur within Internet Explorer. After investigating and confirming that indeed this is an exploitable condition we are alerting people to the true severity of these "crashing" problems that people are experiencing, so that they can take the appropriate mitigation steps as need be.

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