Hackers Circulate Exploit Code For Two Windows Flaws

Exploits and proof-of-concept samples for two recently disclosed critical Microsoft vulnerabilities are circulating among hackers, security experts warned Tuesday. Users who have not yet patched their systems should do so immediately, several security organizations recommended.

Microsoft is aware of both exploits, but doesn't see a threat. "[We are] not currently aware of active attacks utilizing the exploit code," Microsoft spokesperson Kjersti Gunderson said. According to Microsoft's security research center, neither exploit can be used to install or execute code remotely.

Over the weekend, proof-of-concept code for an October vulnerability in Windows was posted by a researcher known only as "Darkeagle" of the "unl0ck" security group, said Cupertino, Calif.-based Symantec in a warning to users of its DeepSight Threat Management System. The French security vendor FrSIRT posted a "critical" warning on the exploit code, which it published in full.

According to Darkeagle, the sample exploit can bring down Windows 2000 systems (including those fully patched to Service Pack 4) with a denial-of-service attack. Microsoft confirmed that Tuesday. "Initial investigation of the exploit code targeting MS05-051 has also verified that successful exploitation could lead to a denial of service attack and not remote code execution," Microsoft's Gunderson said.

This exploit code works against systems vulnerable to the Microsoft Distributed Transaction Coordinator (MSDTC) vulnerability. MSDTC is code used to coordinate any sort of transaction on multiple servers, such as database queries.

When Microsoft disclosed the vulnerability in its Oct. 11 round of security bulletins and patches, many security analysts predicted that an attack would come in short order. The next day, in fact, an exploit was released, but only to customers of a vulnerability research tool. The researcher credited with the discovery of the flaw said that the bug might lead to a repeat of August's Zotob attack, which brought down thousands of PCs worldwide. However, no such attacks occurred.

Now, however, Symantec is warning users to patch their systems as soon as possible. "[Although] the exploit released will only cause a denial of service…the public release of this tool may increase the likelihood of a more sophisticated exploit being released," the company said in its DeepSight alert.

If the patch provided in Microsoft's MS05-051 bulletin can't be applied, Symantec advised administrators to filter TCP port 3372, the default used for MSDTC, at the network edge.

For the moment, there's little cause for alarm, added the SANS Internet Storm Center, which has been monitoring port 3372. "At this point, we see only little activity at port 3372, likely due to the fact that this PoC exploit does not actually execute any 'useful' code," wrote Johannes Ullrich, chief research officer at the ISC, in a note posted on the site.

Also out and about is proof-of-concept code that attacks a second, and newer vulnerability. A researcher from India has posted code that can bring a Windows system to a screeching halt by making IE consume 100 percent of the processor's cycles. On Tuesday, FrSIRT also ranked its alert on this new problem as "Critical."

The exploit leverages a vulnerability in Windows' rendering of WMF and EMF (Windows Metafile and Enhanced Metafile, respectively) images that was disclosed and patched Nov. 8.

Of the three security bulletins released by Microsoft this month, MS05-053, which patches the Metafile bug, was considered the most serious by security experts, even though some dismissed the idea of a major attack. "I think it's doubtful that we'll see this widely exploited," said Neel Mehta, the team leader for Internet Security Systems' (ISS) X-Force research group, at the time.

As with the other bug, Microsoft said that the result of a successful attack "could lead to a denial of service attack and not remote code execution."

Microsoft reminded users that the October and November updates protect against both possible exploits. "[We are] actively monitoring this situation to keep customers informed and to provide customer guidance as necessary," said Microsoft's Gunderson.