Hackers have developed proof-of-concept code that attempts to take advantage of an unpatched Windows vulnerability to crash systems, Microsoft warned (http://www.microsoft.com/technet/security/advisory/911052.mspx) yesterday. Fortunately the risk of attack is low.

The experimental code shows it's possible to knock over machines running Windows XP SP1 and Windows 2000 SP4 in certain configurations by taking advantage of flaws in Windows memory allocation functions. This vulnerability manifests itself when a malformed request is made to the UPnP service in the data section of a call to the GetDeviceList function. In handling this request, memory consumption on vulnerable Windows boxes increase to the point where the system becomes unresponsive. Repeated requests can therefore be used to mount denial of service attacks.

Attacks on Windows XP SP1 would rely on having user authentication, reducing the scope for mischief by remote hackers. Microsoft users running Windows XP Service Pack 2, Windows Server 2003 and Windows Server 2003 Service Pack 1 are not affected by the vulnerability. Win 2000 shops are most at risk but providing systems are properly firewalled then attacks should fail.

Irresponsible disclosure?

Normally the arrival of proof-of-concept illustrates weaknesses that might subsequently by used by hackers for more malign purposes. In this case, however, the attack approach is not especially successful in slowing down systems to a crawl much less as a means to infect vulnerable machines with hostile code. This is a denial of service only risk and the real interest (except to people interested in revisiting the long-running debate about the responsible disclosure of security bugs) is that it is based on an unpatched vulnerability.

Winny Thomas of Nevis Labs in India, the security researcher who developed the proof-of-concept code, readily concedes the Windows RPC memory allocation remote denial of service exploit he highlights is only a moderate risk. Microsoft is yet to develop a security fix. It criticises Thomas of publicising details of the flaw through FrSIRT, a full disclosure web site, instead of submitting it to Microsoft directly first. ®

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