Hackers have posted an exploit which might be used by local users to gain admin privileges on Windows boxes, including machines running Vista. However the bug is not as serious as it might be because initial analysis suggests it can only be exploited locally and not remotely across the internet.
The flaw, such as it is, involves a double-free error in handling of error messages within the WINSRV.DLL library. The bug might be exploited to execute arbitrary code under the Client Server Run-Time Subsystem process with elevated privileges.
Microsoft acknowledged the problem, which it is investigating, while downplaying its significance by pointing out that the flaw does not appear to lend itself to remote exploitation by hackers across the internet.
"The PoC reportedly allows for local elevation of privilege on Windows 2000 SP4, Windows Server 2003 SP1, Windows XP SP1, Windows XP SP2 and Windows Vista operating systems. Initial indications are that in order for the attack to be successful, the attacker must already have authenticated access to the target system," a posting on Microsoft's security response blog explains. ®