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 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.