Published:
20 February 2001
Protect yourself against future threats.
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AUSCERT External Security Bulletin Redistribution
ESB-2001.076 -- Microsoft Security Bulletin MS01-011
Malformed Request to Domain Controller can Cause Denial of Service
21 February 2001
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AusCERT Security Bulletin Summary
---------------------------------
Product: Windows 2000 Server
Windows 2000 Advanced Server
Windows 2000 Datacenter Server
Vendor: Microsoft
Impact: Denial of Service
Access Required: Remote
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Title: Malformed Request to Domain Controller can Cause Denial
of Service
Date: 20 February 2001
Software: Windows 2000 Server, Advanced Server and Datacenter
Server
Impact: Denial of Service
Bulletin: MS01-011
Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS01-011.asp.
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Issue:
======
A core service running on all Windows 2000 domain controllers (but
not on any other machines) contains a flaw affecting how it processes
a certain type of invalid service request. Specifically, the service
should handle the request at issue here by determining that it is
invalid and simply dropping it; in fact, the service performs some
resource-intensive processing and then sends a response.
If an attacker sent a continuous stream of such requests to an
affected machine, it could consume most or all of the machine's CPU
availability. This could cause the domain controller to process
requests for service slowly or not at all, and could limit the number
of new logons the machine could process and the number of Kerberos
tickets that could be issued.
Mitigating Factors:
====================
- The machine would automatically resume normal processing
as soon as the stream of requests ceased.
- Although the attacker could, in theory, use the vulnerability
to completely deny service to network users, in practice the
attack rarely consumes more than 75% of the available CPU
resources.
- Users who were already logged on and were using previously
issued Kerberos tickets would not be affected by domain
controller unavailability.
- If there were multiple domain controllers on the domain, the
unaffected machines could pick up the other machine's load.
- If normal security practices have been followed, Internet
users would be prevented by firewalling and other measures
from levying requests directly to domain controllers.
Patch Availability:
===================
- A patch is available to fix this vulnerability. Please read the
Security Bulletin
http://www.microsoft.com/technet/security/bulletin/ms01-011.asp
for information on obtaining this patch.
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THE FOREGOING LIMITATION MAY NOT APPLY.
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