Protect yourself against future threats.
-----BEGIN PGP SIGNED MESSAGE----- =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2002.538 -- Microsoft Security Bulletin MS02-055 Unchecked Buffer in Windows Help Facility Could Enable Code Execution (Q323255) 03 October 2002 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: Windows Help Facility Vendor: Microsoft Operating System: Windows 98 Windows 98SE Windows ME Windows NT Windows 2000 Windows XP Impact: Execute Arbitrary Code/Commands Access Required: Remote - --------------------------BEGIN INCLUDED TEXT-------------------- - -----BEGIN PGP SIGNED MESSAGE----- - - ---------------------------------------------------------------------- Title: Unchecked Buffer in Windows Help Facility Could Enable Code Execution (Q323255) Date: 02 October 2002 Software: Microsoft Windows 98 Microsoft Windows 98 Second Edition Microsoft Windows Millennium Edition Microsoft Windows NT 4.0 Microsoft Windows NT 4.0, Terminal Server Edition Microsoft Windows 2000 Microsoft Windows XP Impact: Attacker could gain control over user's system Max Risk: Critical Bulletin: MS02-055 Microsoft encourages customers to review the Security Bulletin at: http://www.microsoft.com/technet/security/bulletin/MS02-055.asp. - - ---------------------------------------------------------------------- Issue: ====== The HTML Help facility in Windows includes an ActiveX control that provides much of its functionality. One of the functions exposed via the control contains an unchecked buffer, which could be exploited by a web page hosted on an attacker's site or sent to a user as an HTML mail. An attacker who successfully exploited the vulnerability would be able to run code in the security context of the user, thereby gaining the same privileges as the user on the system. A second vulnerability exists because of flaws associated with the handling of compiled HTML Help (.chm) files that contain shortcuts. Because shortcuts allow HTML Help files to take any desired action on the system, only trusted HTML Help files should be allowed to use them. Two flaws allow this restriction to be bypassed. First, the HTML Help facility incorrectly determines the Security Zone in the case where a web page or HTML mail delivers a .chm file to the Temporary Internet Files folder and subsequently opens it. Instead of handling the .chm file in the correct zone - the one associated with the web page or HTML mail that delivered it - the HTML Help facility incorrectly handles it in the Local Computer Zone, thereby considering it trusted and allowing it to use shortcuts. This error is compounded by the fact that the HTML Help facility doesn't consider what folder the content resides in. Were it to do so, it could recover from the first flaw, as content within the Temporary Internet Folder is clearly not trusted, regardless of the Security Zone it renders in. The attack scenario for this vulnerability would be complex, and involves using an HTML mail to deliver a .chm file that contains a shortcut, then making use of the flaws to open it and allow the shortcut to execute. The shortcut would be able to perform any action the user had privileges to perform on the system. Before deploying the patch, customers should familiarize themselves with the caveats discussed in the FAQ and in the Caveats section below. Mitigating Factors: ==================== Buffer Overrun in HTML Help ActiveX Control: - 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 vulnerability would convey only the user's privileges on the system. Users whose accounts are configured to have few privileges on the system would be at less risk than ones who operate with administrative privileges. Code Execution via Compiled HTML Help File: - The vulnerability could only be exploited if the attacker were able to determine the exact location of the Temporary Internet Files folder. By design, this should not be possible, and Microsoft is unaware of any means for doing so which has not already been patched. - The vulnerability would convey only the user's privileges on the system. Users whose accounts are configured to have few privileges on the system would be at less risk than ones who operate with administrative privileges. Risk Rating: ============ - Internet systems: Moderate - Intranet systems: Moderate - Client systems: Critical Patch Availability: =================== - A patch is available to fix this vulnerability. Please read the Security Bulletin at http://www.microsoft.com/technet/security/bulletin/ms02-055.asp for information on obtaining this patch. Acknowledgment: =============== - David Litchfield of Next Generation Security Software Ltd. (http://www.nextgenss.com/)and Thor Larholm, Security Researcher, PivX Solutions, LLC (http://www.pivx.com) for reporting the Buffer Overrun in HTML Help ActiveX Control. - - --------------------------------------------------------------------- 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. - -----BEGIN PGP SIGNATURE----- Version: PGP 7.1 iQEVAwUBPZuRyI0ZSRQxA/UrAQH8LAf+Pk2vKlAN0ZBOebf9GB6IVarQCIxB3FnX 0W4J21iKLA/DPx7DVAuu5bSuXTd2LqBS2DvF44S5dJ490E2ofZbHP/Xwm+0YqYGV eStH4aHxz+JfLQyU+pa9URk2fYbW04DXq8K8rkzkpjcVDx1S+KNY1RrGUeuzNwcV MNdRvk0nXRjc96V9h/1EsjsO6rfYZVEoE7jh9V7WyGR1YyXZefl7D1S6w76LSPla 0hUhwjt9ebpwno5Jh8sV3E6IgBPXSZ2PkhBnqOUj/A/5Ihgv8qJrzYsp6aSsVaep 3FJxl1D27OYspQt+40fvoRgG3pK2OaUy8F+D/6KweD4/gFDZVSWd8A== =eZtV - -----END PGP SIGNATURE----- - --------------------------END INCLUDED TEXT-------------------- You have received this e-mail bulletin as a result of your organisation's registration with AusCERT. The mailing list you are subscribed to is maintained within your organisation, so if you do not wish to continue receiving these bulletins you should contact your local IT manager. If you do not know who that is, please send an email to auscert@auscert.org.au and we will forward your request to the appropriate person. This security bulletin is provided as a service to AusCERT's members. As AusCERT did not write the document quoted above, AusCERT has had no control over its content. The decision to use any or all of this information is the responsibility of each user or organisation, and should be done so in accordance with site policies and procedures. NOTE: This is only the original release of the security bulletin. It may not be updated when updates to the original are made. If downloading at a later date, it is recommended that the bulletin is retrieved directly from the original authors to ensure that the information is still current. Contact information for the authors of the original document is included in the Security Bulletin above. If you have any questions or need further information, please contact them directly. Previous advisories and external security bulletins can be retrieved from: http://www.auscert.org.au/Information/advisories.html If you believe that your system has been compromised, contact AusCERT or your representative in FIRST (Forum of Incident Response and Security Teams). Internet Email: auscert@auscert.org.au Facsimile: (07) 3365 7031 Telephone: (07) 3365 4417 (International: +61 7 3365 4417) AusCERT personnel answer during Queensland business hours which are GMT+10:00 (AEST). On call after hours for member emergencies only. -----BEGIN PGP SIGNATURE----- Version: 2.6.3i Charset: noconv Comment: ftp://ftp.auscert.org.au/pub/auscert/AUSCERT_PGP.key iQCVAwUBPZyJgSh9+71yA2DNAQEF+AQAkPN8GnXPhyQ4cLDX1CkMRL9OCqzS+R61 WPEbLCyu7oX+ADS2F+YtrPaZek0qetPY2d4sdwmJD9X2RltcFGySTh/PmzKswi2g nmCMzJQoJW2W4/aIRr0g5C5I4M4cFKSvM//4vxpYSHN8SB7lDuJzd/KVjNk8i84w 4JIGzXGtlYc= =Me9R -----END PGP SIGNATURE-----