Microsoft Security Bulletin MS01-013

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Title:      Windows 2000 Event Viewer Contains Unchecked Buffer
Date:       February 26, 2001
Software:   Windows 2000
Impact:     Run code of attacker's choice
Bulletin:   MS01-013

Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS01-013.asp.
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Issue:
======
The Windows 2000 event viewer snap-in has an unchecked buffer in a
section of the code that displays the detailed view of event records.
If the event viewer attempted to display an event record that
contained specially malformed data in one of the fields, either of
two outcomes would result. In the less serious case, the event viewer
would fail. In the more serious case, code of the attacker's choice
could be made to run via a buffer overrun.

By design, unprivileged processes can log events in the System and
Application logs, and interactively logged-on, unprivileged users can
view them. However, only privileged processes can log events in the
Security log, and only interactively logged-on administrators can
view them. If the vulnerability were exploited to run code of the
attacker's choice, the code would run in the security context of the
user who viewed the affected record.

Mitigating Factors:
====================
 - Simply perusing the listing of events in a log would not allow
   the vulnerability to be exploited. It could only be exploited
   if the user opened an affected record to view the event details.
 - Although the Event Viewer is generally thought of as an
   administrative tool, there is no guarantee that the user who opens
   a particular event record would be privileged. Unprivileged users
   can read the System and Application logs. Although the Security
   log can only be read by privileged users, only privileged
   processes can write to it.
 - To the best of our knowledge, it is not possible to manipulate
   the normal auditing functions of any Windows 2000 service in order
   to create an event record that would exploit this vulnerability.
   Instead, a custom piece of code would need to be created and run
   to create such a record.
 - If firewalling and other appropriate precautions have been taken,
   only authenticated users will have access to network machines and
   be able to write event log records.

Patch Availability:
===================
 - A patch is available to fix this vulnerability. Please read the
   Security Bulletin
   http://www.microsoft.com/technet/security/bulletin/ms01-013.asp
   for information on obtaining this patch.

Acknowledgment:
===============
 - Blake Watts of Guardent (http://www.guardent.com)

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