Microsoft Expands IIS Vulnerability Warning

Microsoft on Friday updated the Security Advisory it issued on Tuesday, expanding its warning about a vulnerability in its Internet Information Services (IIS) server software.

Based on additional proof-of-concept exploits that could allow denial-of-service attacks and on limited attempts to exploit the vulnerability, Microsoft now says that IIS 5.0, 5.1, 6.0, and 7.0 are vulnerable to a denial-of-service attacks.

This supersedes Microsoft's previous assertion that "IIS 7.0 (Windows Vista, Windows Server 2008) is not vulnerable."

In addition, users of IIS 5.0 are vulnerable to remote code execution if they allow anonymous FTP.

The IIS vulnerability is related to a stack overflow bug in the IIS FTP module. If an IIS installation allows anonymous FTP, a malicious user could log in and create a directory name so long that it created an overflow condition. A successful attempt to exploit this flaw allows the execution of code in the context of LocalSystem.

Microsoft is advising IIS users to turn off the FTP service unless its needed. It is also recommending that users configure their servers to prevent the creation of new directories and to deny anonymous users write privileges using the appropriate IIS settings.

Microsoft says that it plans to release five "critical" Security Bulletins on Tuesday, September 8, its regularly scheduled "patch day."

It's not clear whether the IIS flaw will be addressed, but given the circumstances under which the vulnerability was disclosed -- a public posting, without prior notification to Microsoft -- it's unlikely that Microsoft will have enough time to thoroughly test a fix for the problem.

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