Published:
08 March 2001
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-----BEGIN PGP SIGNED MESSAGE----- =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2001.107 -- Microsoft Security Bulletin MS01-016 Malformed WebDAV Request Can Cause IIS to Exhaust CPU Resources 9 March 2001 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: IIS 5.0 Vendor: Microsoft Impact: Denial of Service Access Required: Remote - --------------------------BEGIN INCLUDED TEXT-------------------- - -----BEGIN PGP SIGNED MESSAGE----- - - ---------------------------------------------------------------------- Title: Malformed WebDAV Request Can Cause IIS to Exhaust CPU Resources Date: 08 March 2001 Software: IIS 5.0 Impact: Denial of Service Bulletin: MS01-016 Microsoft encourages customers to review the Security Bulletin at: http://www.microsoft.com/technet/security/bulletin/MS01-016.asp. - - ---------------------------------------------------------------------- Issue: ====== 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. Because the discoverer of this vulnerability has chosen to publish code to exploit this vulnerability before a patch could be developed, Microsoft has developed a workaround that can be used to defend against attack. Knowledge Base article Q241520 provides step-by-step instructions for changing the permissions on the .DLL that provides WebDAV services in order to effectively disable it on the machine. When a patch is available, we will re-release this bulletin and provide updated information. Microsoft recommends that customers consider applying the workaround to any servers running IIS 5.0. Although this obviously includes web servers, other services, notably Exchange 2000, may also require that IIS 5.0 be enabled. 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 currently under development and will be released shortly. In the meantime, Knowledge Base article Q241520 (http://www.microsoft.com/technet/support/kb.asp?ID=241520) provides a workaround that can be used to protect against this vulnerability. Please read the Security Bulletin http://www.microsoft.com/technet/security/bulletin/ms01-016.asp for more information on this vulnerability. - - --------------------------------------------------------------------- THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY. - -----BEGIN PGP SIGNATURE----- Version: PGP Personal Privacy 6.5.3 iQEVAwUBOqgEso0ZSRQxA/UrAQEfuAf7B/9Ba0KygUxx4GYoPaNQu6mmwlJ7nQy1 firxtPeQPSaNriq8mHKPPh1lvWrlSX0iCaIA4UP7bS7By94NBAwGB4h0vmcmwAvT bL0U0bPJZRPeRs7OQpkztzOLUlmCbvHHK7QoHhQ+QY7TmNzM6uXjXJ/jVJZVPZpo a3gKPrRyR0gXPzN2g10i4rHMKGROe+yRWmQvTh4lRXMATD0d59H5me1MvVbGSa5W pNnKbeOZPpphQVMIqjZflNaLko7ccUjL4Wu/ldNUl31bQGdZkB2izoqieuhwU1mQ F2wfVzLkBmQF+CLooFtzurX9FVvTbwOys3ZPVWitZILUL3dvmbs+RQ== =zZRX - -----END PGP SIGNATURE----- - --------------------------END INCLUDED TEXT-------------------- This security bulletin is provided as a service to AusCERT's members. As AusCERT did not write the document quoted above, AusCERT has had no control over its content. The decision to use any or all of this information is the responsibility of each user or organisation, and should be done so in accordance with site policies and procedures. NOTE: This is only the original release of the security bulletin. It may not be updated when updates to the original are made. If downloading at a later date, it is recommended that the bulletin is retrieved directly from the original authors to ensure that the information is still current. Contact information for the authors of the original document is included in the Security Bulletin above. If you have any questions or need further information, please contact them directly. Previous advisories and external security bulletins can be retrieved from: http://www.auscert.org.au/Information/advisories.html If you believe that your system has been compromised, contact AusCERT or your representative in FIRST (Forum of Incident Response and Security Teams). Internet Email: auscert@auscert.org.au Facsimile: (07) 3365 7031 Telephone: (07) 3365 4417 (International: +61 7 3365 4417) AusCERT personnel answer during Queensland business hours which are GMT+10:00 (AEST). On call after hours for emergencies. -----BEGIN PGP SIGNATURE----- Version: 2.6.3i Charset: noconv Comment: ftp://ftp.auscert.org.au/pub/auscert/AUSCERT_PGP.key iQCVAwUBOqj/Fyh9+71yA2DNAQEDRwQAhycfwhYUOQHG3jXVU8DrHFA6EaCEKCkW EcmjkebWs9htqV5sivuLLCWaISDwOJijqaMpwcQeG+IEYFdwLwXrpHAioUCl9ORC tjBqDke4Gl4XgDAFkIKLkWNNwRKg1mFgAlRpmjlNbbOO741rohQ9yt8KBirUjzXK r0exnC+RTIw= =1SPV -----END PGP SIGNATURE-----