Microsoft exploit code circulating

Security researchers say code designed to exploit a recently announced critical vulnerability in Microsoft operating systems now is widespread on the Internet.

The code crashes targeted computers by exploiting a flaw in Microsoft’s Abstract Syntax Notation 1 Library in Windows NT, 2000 and XP. The exploit code was discovered Saturday, four days after the vulnerability and a patch to correct it was announced by Microsoft.

"The exploit we discovered is fully functional and does cause targeted computers to crash," said Ken Dunham, director of malicious code for iDefense Inc. of Reston, Va. "The widespread distribution of this code has significantly increased the threat level for ASN.1."

The code is available on several discussion groups and Web sites.

Dunham said there have been reports of denial-of-service attacks against specific targets using this exploit, but the attacks are not yet widespread. "It may be a few days before we see anything beyond a DOD attack," he said. "Several attackers are actively working on an ASN.1 exploit to spread Trojans and ‘bots. One attacker has expressed an interest in creating a worm that will ‘take down the Internet,’" reports &to=http://www.gcn.com' target=_blank>GCN

The leak of Windows source code last week has already enabled a hacker to create an exploit. Days after portions of the Microsoft Windows 2000 and Windows NT 4.0 source code were illegally leaked onto the Web, an anonymous hacker has found a buffer overflow flaw and crafted an exploit. The attack relies on a vulnerability in the way that IE 5 processes bitmap files. This could allow an attacker to inject hostile code into vulnerable systems, according to an advisory published by the Security Tracker vulnerability database, informs &to=http://www.theregister.co.uk' target=_blank>TheRegister