Microsoft Issues Bulletin Re: Microsoft IIS 5.0 Web Server Can Be Restarted Remotely By Any User
SecurityTracker Alert ID: 1001053|
SecurityTracker URL: http://securitytracker.com/id/1001053
(Links to External Site)
Date: Mar 9 2001
Denial of service via network|
Vendor Confirmed: Yes |
Georgi Guninski reports a vulnerability with Microsoft's Internet Information Server (IIS) v5.0 in which a remote user can send a certain packet to the server, causing the server to automatically restart|
Microsoft has issued a bulletin (MS01-016) regarding this vulnerability. Microsoft confirms that malformed WebDAV requests can cause IIS to exhaust all CPU resources.
WebDAV is an extension to the HTTP protocol that permits remote authoring and management of web content. According to the vendor, IIS 5.0 under Windows 2000 performs some initial processing of all WebDAV requests, then forwards the relevant commands to the WebDAV process. The manner in which WebDAV handles a particular type of malformed request results in this vulnerability. If a stream of malformed requests is directed at an IIS 5.0 server, the WebBAV process would reportedly use up all CPU resources on the server.
For more information, see:
A remote user with access to the web server's port (which is basically everyone in the case of a public web server) can cause the server to crash and restart.|
Microsoft has developed a workaround that is described in Knowledge Base article Q241520 to effectively disable WebDAV on the server. Microsoft will issue a patch at a future date.|
Vendor URL: www.microsoft.com/technet/security/bulletin/MS01-016.asp (Links to External Site)
Boundary error, State error|
|Underlying OS: Windows (2000)|
This archive entry is a follow-up to the message listed below.|
Source Message Contents
Subject: Microsoft Security Bulletin MS01-016|
The following is a Security Bulletin from the Microsoft Product Security
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
Date: 08 March 2001
Software: IIS 5.0
Impact: Denial of Service
Microsoft encourages customers to review the Security Bulletin at:
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.
- The effect of an attack via this vulnerability would be temporary.
server would automatically resume normal service as soon as the
requests stopped arriving.
- The vulnerability does not provide an attacker with any capability
carry out WebDAV requests.
- The vulnerability does not provide any capability to compromise
the server or gain administrative control over it.
- A patch is currently under development and will be released
the meantime, Knowledge Base article Q241520
provides a workaround that can be used to protect against this
Please read the Security Bulletin
for more information on this vulnerability.
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