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Exploit based on leaked Windows code released
Patrick Gray, SecurityFocus 2004-02-16

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.

"Yes, there are tons of new eyes looking at this Microsoft source code, but these people will do the same sort of analysis that has already been done," he said. "People who have been finding new holes in XP and Windows 2000 have done so without knowledge of the source. But the bottom line is that we don't know."

Gula pointed out that historically the exposure of source code had not spelled catastrophe for vendors. "Cisco IOS has been 'out there' for a long time as well and we have not seen huge spikes in Cisco vulnerabilities," he said.

Others, like U.S. Department of the Interior security systems specialist Robert Ferrell, point out the source code that hit peer-to-peer networks last Friday was fairly old, but concede some new vulnerabilities will most likely be uncovered. "I'd wager... that the majority of the vulnerabilities in this code have already been discovered and patched," he said in an e-mail interview. "[That's] not to say that there won't be further exploits... I think that's more or less a given."

A security researcher with Miscname.com, who did not wish to be named, tested GTA's exploit, and said the basic proof-of-concept file could easily be modified to execute arbitrary code on vulnerable systems. He said a particular concern is the vulnerability appears to be eradicated by a Service Pack, instead of a stand-alone patch or "hotfix". Because of the strict licensing controls on Windows XP, those using a pirated copies of the operating system would not be able to download the service pack, he said, which could create problems for the wider online community.

Systems in countries where piracy is rampant could be left exposed if a specific patch is not released by Microsoft, he said. These vulnerable hosts could be compromised and loaded with denial of service "zombie" agents, keystroke loggers, or used as spam relays, a problem that would affect everyone, he said. "The last thing that we need out there is more zombies."


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