Title: Buffer Overrun in TSAC ActiveX Control Could Allow Code Execution (Q327521) Date: 22 August 2002 Software: Microsoft Terminal Services Advanced Client (TSAC) ActiveX control, which can be installed on any Windows system. Impact: Run code of the attacker's choice Max Risk: Moderate Bulletin: MS02-046
Microsoft encourages customers to review the Security Bulletin at: http://www.microsoft.com/technet/security/bulletin/MS02-046.asp
The Terminal Services Advanced Client (TSAC) web control is an ActiveX control that can be used to run Terminal Services sessions within Internet Explorer. The downloadable ActiveX control provides nearly the same functionality as the full Terminal Services Client, but is designed to deliver this functionality over the Web.
The TSAC control does not come installed as part of any Windows client system. Instead, clients obtain the control from web servers that offer terminal services. The configuration process that enables an IIS server to provide terminal services involves installing on the server a cabinet file containing the control. The server then delivers the cabinet file to any client system that needs it, and the client installs the control via the cabinet file.
A security vulnerability results because the control contains an unchecked buffer in the code that processes one of the input parameters. By calling the control on a client system and overrunning the buffer, an attacker could gain the ability to run code in the security context of the currently logged on user. This would enable the attacker to take any desired action on the user's system. The attacker could mount an attack by either hosting a web page that exploits the vulnerability against any user who visits it, or by sending an HTML mail to another user.
The vulnerability could only be exploited if the TSAC control had been installed on the user's system by an IIS server hosting the control.
The vulnerability poses no threat to servers that host it. While housed on the server, the control is encapsulated in a cabinet file and cannot be executed.
The HTML mail-based attack vector could not be exploited on systems where Outlook 98 or Outlook 2000 were used in conjunction with the Outlook Email Security Update, or Outlook Express 6 or Outlook 2002 were used in their default configurations
THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND. MICROSOFT DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. IN NO EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. SOME STATES DO NOT ALLOW THE EXCLUSION OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES SO THE FOREGOING LIMITATION MAY NOT APPLY.