Vulnerability Note VU#959211

Microsoft IIS vulnerable to DoS via invalid request for very long WebDAV requests

Overview

Intruders can disrupt the normal operation of an IIS 5.0 server using a malicious Web Distributed Authoring and Versioning (WebDAV) request.

I. Description

WebDAV is an extension to HTTP used to manage content on web servers. Quoting from RFC 2518:

[WebDAV is] an extension to the HTTP/1.1 protocol that allows clients to perform remote web content authoring operations. This extension provides a coherent set of methods, headers, request entity body formats, and response entity body formats that provide operations for: Properties [...], Collections [... and], Namespace Operations.

A vulnerability in the Microsoft implementation of WebDAV can be used to disrupt IIS 5.0. Quoting from MS01-044,

A denial of service vulnerability [exists] that could enable an attacker to temporarily disrupt service on an IIS 5.0 web server. WebDAV doesn't correctly handle [a] particular type of very long, invalid request. Such a request would cause the IIS 5.0 service to fail; by default, it would automatically restart.

WebDAV is installed and operational by default on Microsoft IIS 5.0. This does not affect IIS 4.0 servers.

II. Impact

An intruder can cause the IIS 5.0 service to fail. It will restart by default.

III. Solution

Apply a patch as described in MS01-044. This is a cumulative patch that addresses a number of security problems discovered prior to August 15, 2001.

Systems Affected

Vendor	Status	Date Notified	Date Updated
Microsoft	Vulnerable	18-Sep-2001

References

http://www.microsoft.com/technet/treeview/default.asp?url=/technet/security/bulletin/ms01-044.asp
http://www.securityfocus.com/bid/3194
http://www.ietf.org/rfc/rfc2518.txt

Credit

This document was written by Shawn Hernan, based upon information in Microsoft Security Bulletin MS01-044.

Other Information

Date Public:	2001-08-15
Date First Published:	2001-09-18
Date Last Updated:	2001-09-18
CERT Advisory:
CVE-ID(s):	CAN-2001-0508
NVD-ID(s):	CAN-2001-0508
US-CERT Technical Alerts:
Metric:	12.60
Document Revision:	11

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