Exploit based on leaked Windows code released

The first new security vulnerability to emerge from last week's Microsoft source code leak crossed a security mailing list over the weekend, reigniting debate over the seriousness of the leak. The vulnerability affects Internet Explorer 5 and various versions of Outlook Express. It was unearthed in code the two programs use to process bitmap image files, and affects the software on several versions of Windows, including 98, 2000 and XP. While some systems appear to be immune to the glitch, a proof-of-concept exploit that was posted to the Full Disclosure mailing list crashes Outlook Express 6 on Windows XP systems. Service Pack 1 appears to correct the vulnerability.

The exploit is a carefully-constructed bitmap file that "clobbers the stack" with data when opened in a vulnerable application, according to the author of the exploit, who calls himself "GTA." By corrupting a targeted system's memory in a controlled way, an attacker could likely use the flaw to execute arbitrary code on a vulnerable machine.

While some commentators expect last week's source code leak to lead to the release of a plethora of exploits, others are more conservative. The original author of the Dragon Intrusion Detection System and CTO of Tenable Network Security, Ron Gula, is reserving his judgment.

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