Title: Unchecked Buffer in ISAPI Filter Could Allow Commerce
Server Compromise
Date: 21 February 2002
Software: Commerce Server 2000
Impact: Run code of attacker's choice.
Max Risk: Critical
Bulletin: MS02-010

Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS02-010.asp.

Issue:

By default, Commerce Server 2000 installs a .dll with an ISAPI
filter that allows the server to provide extended functionality in
response to events on the server. This filter, called AuthFilter,
provides support for a variety of authentication methods.
Commerce Server 2000 can also be configured to use other
authentication methods.

A security vulnerability results because AuthFilter contains an
unchecked buffer in a section of code that handles certain types
of authentication requests. An attacker who provided
authentication data that overran the buffer could cause the
Commerce Server process to fail, or could run code in the
security context of the Commerce Server process. The
process runs with LocalSystem privileges, so exploiting the
vulnerability would give the attacker complete control of
the server.

Mitigating Factors:

• Although Commerce Server 2000 does rely on IIS for its base
  web services, the AuthFilter ISAPI filter is only available
  as part of Commerce Server. Customers using IIS are at no
  risk from this vulnerability.

• The URLScan tool, if deployed using the default ruleset for
  Commerce Server, would make it difficult if not impossible
  for an attacker to exploit the vulnerability to run code,
  by significantly limiting the types of data that could be
  included in an URL. It would, however, still be possible
  to conduct denial of service attacks.

• An attacker's ability to extend control from a compromised
  web server to other machines would depend heavily on the
  specific configuration of the network. Best practices recommend
  that the network architecture account for the inherent high-risk
  that machines in an uncontrolled environment, like the Internet,
  face by minimizing overall exposure though measures like DMZ's,
  operating with minimal services and isolating contact with
  internal networks. Steps like this can limit overall exposure
  and impede an attacker's ability to broaden the scope of a
  possible compromise.

• While the ISAPI filter is installed by default, it is not loaded
  on any web site by default. It must be enabled through the
  Commerce Server Administration Console in the Microsoft
  Management Console (MMC).

Risk Rating:

• Internet systems: Critical
• Intranet systems: Critical
• Client systems: None

Patch Availability:

• A patch is available to fix this vulnerability. Please read the
  Security Bulletin at
  http://www.microsoft.com/technet/security/bulletin/ms02-010.asp
  for information on obtaining this patch.

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