AUSCERT External Security Bulletin Redistribution

    ESB-2001.116 -- Microsoft Security Bulletin MS01-016 (version 2.0)
      Malformed WebDAV Request Can Cause IIS to Exhaust CPU Resources
                               15 March 2001


        AusCERT Security Bulletin Summary

Product:                IIS 5.0
Vendor:                 Microsoft
Impact:                 Denial of Service
Access Required:        Remote

Ref:                    ESB-2001.107

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The following is a Security  Bulletin from the Microsoft Product Security
Notification Service.

Please do not  reply to this message,  as it was sent  from an unattended


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Title:      Malformed WebDAV Request Can Cause IIS
            to Exhaust CPU Resources
Released:   08 March 2001
Revised:    13 March 2001 (version 2.0)
Software:   IIS 5.0
Impact:     Denial of Service
Bulletin:   MS01-0016

Microsoft encourages customers to review the Security Bulletin at:
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Reason for Revision:
The original version of this bulletin provided a workaround
(discussed in Knowledge Base article Q241520) that would protect
affected systems by disabling WebDAV services. However, a security
patch is now available that eliminates the vulnerability, and
Microsoft recommends using the patch rather than the workaround. We
have updated both the bulletin and the narrative below to reflect

WebDAV is an extension to the HTTP protocol that allows remote
authoring and management of web content. In the Windows 2000
implementation of the protocol, IIS 5.0 performs initial processing
of all WebDAV requests, then forwards the appropriate commands to the
WebDAV process. However, a flaw exists in the way WebDAV handles a
particular type of malformed request. If a stream of such requests
were directed at an affected server, it would consume all CPU
availability on the server.

The patch should be applied to all machines running IIS 5.0. While
this obviously includes web servers, it's worth noting that IIS 5.0
may be running on other types of servers as well, particularly mail
servers running Exchange 2000.

Mitigating Factors:
 - The effect of an attack via this vulnerability would be
   temporary. The server would automatically resume normal
   service as soon as the malformed requests stopped arriving.

 - The vulnerability does not provide an attacker with any
   capability to carry out WebDAV requests.

 - The vulnerability does not provide any capability to
   compromise data on the server or gain administrative
   control over it.

Patch Availability:
 - A patch is available to fix this vulnerability. Please read the
   Security Bulletin
   for information on obtaining this patch.

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