[CORE SDI ADVISORY] MS NT4.0 Terminal Server Edition GINA buffer overflow

[Iván Arce <core.lists.bugtraq () CORE-SDI COM>]

                                                            CORE SDI
                                                http://www.core-sdi.com

         Vulnerability Report For Microsoft Windows NT 4.0 Terminal Server
GINA

Date Published: 2000-11-08

Advisory ID: CORE-20001108

Bugtraq ID: 1924

CVE CAN: Non currently assigned.

Title: Windows NT 4.0 Terminal Server RegAPI.DLL Buffer Overflow

Class: Boundary Error Condition (Buffer Overflow)

Remotely Exploitable: Yes

Locally Exploitable: Yes

Release Mode: COORDINATED RELEASE

Vulnerability Description:

  GINA stands for Graphical Identification aNd Authorization and describes
  an interface for the validation of logon credentials. The default
  implementation is MSGINA.DLL.

  The MSGINA.DLL in Microsoft Windows 4.0 is responsable of performing the
  authentication policy of the interactive logon model, and is expected to
  perform all identification and authentication user interactions.

  Microsoft Windows NT 4.0 Terminal Server ships with a remotely and locally
  exploitable buffer overflow in a Dinamically Linked Library  (RegAPI.DLL)
  that MSGINA.DLL uses.

  It could be exploited by entering a long string in the username field.
  This buffer overflow when being triggered will result in a system crash
  (if triggered locally) or a connection drop (if triggered remotely).

  By providing a specially crafted username an attacker has the ability
  to obtain access to the Terminal Server and execute arbitrary commands
  as user SYSTEM.

Vulnerable Packages/Systems:

  Microsoft Windows NT 4.0 Terminal Server Edition SP6a and below

Solution/Vendor Information/Workaround:

  Microsoft has released a fix for the problem, it can be obtained
  from http://www.microsoft.com/Downloads/Release.asp?ReleaseID=25565

  More Information:

  Please see the following references for more information related
  to this issue.

  Frequently Asked Questions:

    Microsoft Security Bulletin MS00-087,
    http://www.microsoft.com/technet/security/bulletin/fq00-087.asp

   Microsoft Knowledge Base article Q277910 discusses this issue and
   will be available soon.

   Microsoft TechNet Security web site,
   http://www.microsoft.com/technet/security/default.asp

   Additionally, advisories and information on security issues  concerning
   Windows NT 4.0 Terminal Server Edition can be  obtained from:

   http://www.securityfocus.com/bid/571
   http://www.microsoft.com/technet/security/bulletin/fq99-028.asp

  Other advisories from CORE SDI can be obtained from:
   http://www.core-sdi.com/english/publications.html

Vendor notified on: October 3rd, 2000

Credits:

  This vulnerability was discovered by Bruno Acselrad of
  CORE SDI S.A., Buenos Aires, Argentina.

  We wish to thank the Microsoft Security Team for their prompt
  acknowledge and response to the problem report.

  This advisory was drafted with the help of the SecurityFocus.com
  Vulnerability Help Team. For more information or assistance drafting
  advisories please mail vulnhelp () securityfocus com.

Technical Description - Exploit/Concept Code:

  Windows NT 4.0 Terminal Server has a remote and locally exploitable
  buffer overflow in the GINA subsystem.

  Entering a long username in the username edit box will make the
  system crash (if done locally) or drop the connection (if done remotely).

  The problem occurs when MSGINA.DLL calls the ReUserConfigQuery() function
  in RegAPI.DLL.

  Within that function wscpy() is first called and then wscat() appends to a
  local variable of fixed lenght a fixed key and the username string.

  This local variable can be overflowed resulting in the execution of
  arbitrary commands on the vulnerable host.

DISCLAIMER:
  The contents of this advisory are copyright (c) 2000 CORE SDI S.A.
  and may be distributed freely provided that no fee is charged for this
  distribution and proper credit is given.

$Id: NT4TS-gina-advisory.txt,v 1.6 2000/11/09 00:03:51 iarce Exp $

---

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Iván Arce
Presidente
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