Free tools help protect users from IIS zero-day exploit

Security and patch management vendor Shavlik Technologies Tuesday recommended a pair of free tools from Microsoft to help users protect themselves from a zero-day exploit in Internet Information Server.

Eric Schultze, CTO of Shavlik, says the IIS Lockdown Tool and the URLScan Tool, both available for free from Microsoft, will provide protection for users until Microsoft decides if it will release a formal patch.

Microsoft has not promised a patch. The company's next Patch Tuesday release is slated for June 9.

URLScan v3.1 is an ISAPI filter that reads configuration from an Urlscan.ini file and restricts certain types of HTTP requests from being executed by IIS, according to Microsoft's Web site. The tool installs on IIS 5.1 and later.

The IIS Lockdown Tool can be used on IIS 5.0. The 6.0 and 7.0 versions of IIS have similar built-in security configuration tools and users don't need to run the Lockdown tool on Web servers running those IIS versions.

Schultze says the zero-day flaw appears to be more serious in IIS 5.0 on Windows 2000 because the vulnerable WebDAV services are running by default. He points out that IIS 6.0 on Windows Server 2003 doesn't enable WebDAV by default.

Schultze says it's unclear the level of access an attacker can gain via this exploit. Factors in the depth of the exploit include how the Web server has been configured and how the file system security has been applied to the data on the Web server.

"If the attacker is unable to write any files to the Web server, it's far less likely that the attacker can upload or execute any malicious code on the server or gain additional levels of access to the server," he says.

But he did note that the flaw could enable attackers to read code pages on the Web server, and code pages might include usernames or passwords for applications or databases controlled by the Web server.

Schultze recommends people running IIS 5.0 or 6.0 use the IIS Lockdown and URLScan tools. Both tools disable WebDAV and will protect systems from this latest vulnerability, he says.

Schultze points out that the zero-day flaw is only the third vulnerability in IIS since October of 2004. The other two were seen in July 2006 and February 2008.

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