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CERT: Denial-of-Service Still Possible on W2K Systems with RPC Patch

The CERT Coordination Center put out a warning that Windows 2000 systems remain vulnerable to a denial-of-service attack even after applying the critical and high-profile RPC patch Microsoft issued in mid-July.

The Remote Procedure Call (RPC) patch, also known by its Microsoft Security Bulletin identifier, MS03-026, blocks a severe vulnerability that could allow an attacker to take control of users' machines over the Internet. Affected versions of Windows include Windows XP, Windows 2000, Windows NT 4.0 and Windows Server 2003.

That vulnerability seems ripe for a damaging worm, similar to Code Red or Nimda. Security firms have noted an increase in Internet scanning of the affected ports (135, 139 and 445) for vulnerabilities and several coder groups have published exploit code.

What the CERT/CC security incident team is now responding to is a less severe, and apparently separate, flaw in RPC that can allow a denial-of-service attack on Windows 2000.

"Systems running Windows 2000 may still be vulnerable to at least a denial-of-service attack … if their [Distributed Component Object Model Remote Procedure Call] service is available via the network," CERT/CC reports in an advisory updated Friday. "Exploit code for this vulnerability has been publicly released and also targets TCP port 135.

While Microsoft has confirmed that Windows 2000 is vulnerable to this second RPC flaw, no solution is available to fix the underlying problem. Microsoft and the CERT/CC both recommend that affected sites block UDP and TCP services on ports 135, 139 and 445.

The CERT advisory is available here:
www.cert.org/advisories/CA-2003-19.html.

About the Author

Scott Bekker is editor in chief of Redmond Channel Partner magazine.

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