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Title: Unchecked Buffer in Index Server ISAPI Extension Could
Enable Web Server Compromise
Date: 18 June 2001
Software: Index Server 2.0 and Indexing Service
Impact: Run code of attacker's choice
Bulletin: MS01-033

Microsoft encourages customers to review the Security Bulletin at:
http://www.microsoft.com/technet/security/bulletin/MS01-033.asp.

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Issue:

As part of its installation process, IIS installs several ISAPI
extensions – .dlls that provide extended functionality. Among these
is
idq.dll, which is a component of Index Server (known in Windows 2000
as
Indexing Service) and provides support for administrative scripts
(.ida
files) and Internet Data Queries (.idq files).

A security vulnerability results because idq.dll contains an
unchecked
buffer in a section of code that handles input URLs. An attacker who
could establish a web session with a server on which idq.dll is
installed could conduct a buffer overrun attack and execute code on
the
web server. Idq.dll runs in the System context, so exploiting the
vulnerability would give the attacker complete control of the server
and allow him to take any desired action on it.

The buffer overrun occurs before any indexing functionality is
requested. As a result, even though idq.dll is a component of Index
Server/Indexing Service, the service would not need to be running in
order for an attacker to exploit the vulnerability. As long as the
script mapping for .idq or .ida files were present, and the attacker
were able to establish a web session, he could exploit the
vulnerability.

Clearly, this is a serious vulnerability, and Microsoft urges all
customers to take action immediately. Customers who cannot install
the
patch can protect their systems by removing the script mappings for
.idq and .ida files via the Internet Services Manager in IIS.
However,
as discussed in detail in the FAQ, it is possible for these mappings
to
be automatically reinstated if additional system components are added
or removed. Because of this, Microsoft recommends that all customers
using IIS install the patch, even if the script mappings have been
removed.

Mitigating Factors:

• The vulnerability can only be exploited if a web session
  can be established with an affected server. Customers
  who have installed Index Server or Index Services but not
  IIS would not be at risk. This is the default case for
  Windows 2000 Professional.
• The vulnerability cannot be exploited if the script mappings
  for Internet Data Administration (.ida) and Internet Data
  Query (.idq) files are not present. The procedure for
  removing the mappings is discussed in the IIS 4.0
  (http://www.microsoft.com/technet/security/iischk.asp) and IIS
  5.0 (http://www.microsoft.com/technet/security/iis5chk.asp)
  Security checklists, can be automatically removed via either
  the High Security Template or the Windows 2000 Internet Server
  Security Tool
  (http://www.microsoft.com/technet/security/tools.asp).
  Customers should be aware, however, that subsequently adding
  or removing system components can cause the mapping to be
  reinstated, as discussed in the FAQ.
• 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.

Patch Availability:

• A patch is available to fix this vulnerability. Please read the
  Security Bulletin
  http://www.microsoft.com/technet/security/bulletin/ms01-033.asp
  for information on obtaining this patch.

Acknowledgment:

• eEye Digital Security (http://www.eeye.com)

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