Just a day after downplaying the vulnerability that caused it to issue an out-of-cycle patch last week, Microsoft warned customers that exploit code is being used in additional attacks.
"We've identified the public availability of exploit code that now shows code execution for the vulnerability addressed by MS08-067," said Mike Reavey, operations manager of Microsoft's Security Response Center, in a post to the MSRC blog Monday evening. "This exploit code has been shown to result in remote code execution on Windows Server 2003, Windows XP, and Windows 2000."
Microsoft also posted a security advisory to its website that outlined the new threat.
On Tuesday, a company spokesman declined to specify where Microsoft had found the attack code, saying only that the new warning came after Microsoft became "aware of detailed, reliable, public exploit code." He also confirmed that the warning stemmed from code published to the web, not the appearance of an exploit module in a proprietary penetration testing application.
Just the day before, another Microsoft employee had downplayed the threat posed by the bug in the Windows Server service that Microsoft patched last week - outside its regularly once-a-month schedule.
"We are aware that people are working to develop reliable public exploit code for the vulnerability," acknowledged Christopher Budd, a spokesman for the MSRC, in an entry he wrote Sunday. "We are aware of discussion about code posted on a public site, but our analysis has shown that code always results in a denial of service.
"So far, we've not seen evidence of public, reliable exploit code showing code execution," Budd concluded then.
Previously, Microsoft said that it discovered the vulnerability after a small number of attacks had resulted in infections by an information-stealing Trojan, which it dubbed "Win32/MS08067.gen!A" and third-party anti-virus vendors tagged with their own names. Symantec, for example, called it "Trojan.Gimmiv."
It was unclear whether the just-published exploit code that Microsoft referenced on Monday was in fact the same exploit used in those earlier attacks.
On Monday, Reavey repeated earlier Microsoft assertions that attacks remained scattered. "Attacks are still limited and targeted, even with the release of this new exploit code," he said. "The malware situation remains the same, as we've not seen any self-replicating worms, but instead malware that would be classified as Trojans, specifically the malware we discussed when we released the security update on Thursday."
Users who have deployed the patch presented by MS08-067 last week are safe from attack by the published exploit, Reavey added.
The security bulletin that spells out the vulnerability is available on Microsoft's site, and the patch can be downloaded manually or retrieved using the company's Windows Update service.