L-081: Microsoft Index Server Search Function Buffer Overflow [Microsoft Security Bulletin MS01-025] May 14, 2001 18:00 GMT -------------------------------------------------------------------------------- PROBLEM: An unchecked buffer exists in software processing search requests. This causes several potential vulenrabilities, depending on the format of an attacker's search request. PLATFORM: Indexing Service for Windows 2000, Index Server 2.0, DAMAGE: An attacker could run the code of choice within Local Security context, or cause denial of service to the Index server. Or, it could result in unauthorized file disclosure. SOLUTION: Apply the patch described below. -------------------------------------------------------------------------------- VULNERABILITY ASSESSMENT: MEDIUM to HIGH, depending on network configuration. This exploit requires access to Netbios across the network, so this is only exploitable if Netbios allowed through firewalls. It is remotely exploitable. -------------------------------------------------------------------------------- [****** Start Microsoft Advisory ******] ----------------------------------------------------------------------- Title: Index Server Search Function Contains Unchecked Buffer Date: 10 May 2001 Software: Index Server 2.0, Indexing Service for Windows 2000 Impact: Run code of attacker's choice; file disclosure Bulletin: MS01-025 Microsoft encourages customers to review the Security Bulletin at: http://www.microsoft.com/technet/security/bulletin/MS01-025.asp. ----------------------------------------------------------------------- Issue: ====== The patches provided in the bulletin address two security vulnerabilities that are unrelated to each other except in the sense that both affect Index Server 2.0. The first vulnerability is a buffer overrun vulnerability. Index Server 2.0 has an unchecked buffer in a function that processes search requests. If an overly long value were provided for a particular search parameter, it would overrun the buffer. If the buffer were overrun with random data, it would cause Index Server to fail. If it were overrun with carefully selected data, code of the attacker's choice could be made to run on the server, in the Local System security context. The second vulnerability affects both Index Server 2.0 and Indexing Service in Windows 2000, and is a new variant of the "Malformed Hit-Highlighting" vulnerability discussed in Microsoft Security Bulletin MS00-006 (http://www.microsoft.com/technet/security/bulletin/MS00-006.asp). The new variant has almost the same scope as the original vulnerability, but potentially exposes a new file type If an attacker provided an invalid search request, she could read "include" files residing on the web server. The new patch eliminates all known variants of the vulnerability. Mitigating Factors: ==================== Index Server 2.0 buffer overrun: - The vulnerability only affects Index Server 2.0. Indexing Services in Windows 2000 is not affected by it. - In order to exploit the vulnerability, the attacker would need the ability to authenticate to the server and to create a named pipe connection to it (which requires access to NetBIOS, which should be blocked at the firewall). As a result, it is likely that this vulnerability could, in a properly configured network, only be exploited by an intranet user. - Index Server 2.0 is not provided as part of Windows NT 4.0; instead, it is part of the Windows NT 4.0 Option Pack. It installs by default as part of that package, but does not run by default. New Variant of "Malformed Hit-Highlighting" vulnerability: - The vulnerability would only allow files to be read. They could not be added, changed or deleted via this vulnerability. - Server-side "include" files should not contain sensitive data. If this recommendation has been followed, there would be no sensitive data to compromise via this vulnerability. - The vulnerability would only allow files residing on the web server - and in the same logical drive as the server's root directory - to be read. It would not allow files elsewhere on the server, or files residing on a remote server, to be read. Patch Availability: =================== - A patch is available to fix this vulnerability. Please read the Security Bulletin http://www.microsoft.com/technet/security/bulletin/ms01-025.asp for information on obtaining this patch. Acknowledgment: =============== - David Litchfield of @Stake (http://www.atstake.com) for reporting the Index Server 2.0 buffer overrun. - Mike Mulling (http://www.gap.com) for reporting the new variant of the "Malformed Hit-Highlighting" vulnerability ---------------------------------------------------------------------- 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. [****** End Microsoft Advisory ******]