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From: NGSSoftware Insight Security Research (nisr_at_nextgenss.com)
Date: Thu Oct 31 2002 - 11:17:17 CST
NGSSoftware Insight Security Research Advisory
Name: IIS 5 & 5.1 Denial Of Service Vulnerability
Systems Affected: Windows 2000 and XP all service packs.
Category: Denial of Service
Vendor URL: http://www.mircosoft.com
Author: Mark Litchfield (markngssoftware.com)
Date: 31st October 2002
Advisory number: #NISR31102002
Microsofts Internet Information Server and Intranet Server 5.0 and 5.1 comes
with a feature called WebDAV. WebDAV, or Web-based Distributed Authoring and
Versioning, is the emerging standard in web-based collaboration. Simply put,
WebDAV allows web development teams and other workgroups to use a remote web
server as easily as if it were a local file server. Technically, WebDAV is a
set of extensions to the HTTP protocol.
In this particular instance, a denial of service vulnerability exists due to
a flaw in the way IIS 5.0 and 5.1 allocates memory for WebDAV requests. If a
malformed WebDAV request was sent to the server, IIS would allocate an
extremely large amount of memory on the server. By sending several such
requests, an attacker could cause the server to fail. This vulnerability
could only be exploited if the server allowed WebDAV requests to be levied
on it and is also dependent upon the Indexing server service to be running.
Whilst by default the relevant WebDAV request method is allowed, the
Indexing Service is turned off by default.
NGSSoftware alerted Microsoft to these problems on the 16th May 2002. A
patch can be found at
Common Vulnerabilities & Exposures
A check for these issues has been added to Typhon II, of which more
information is available from the