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Microsoft SQL Server Restore Integer Underflow Vulnerability

07.08.08

BACKGROUND

SQL Server is Microsoft's database server product. It supports the restoration and inspection of backups via SQL statements. For more information see the vendor's website found at the following URL.

http://www.microsoft.com/sql/default.mspx

DESCRIPTION

Remote exploitation of an integer underflow vulnerability within Microsoft Corp.'s SQL Server could allow a remote attacker to execute arbitrary code with the privileges of the SQL Server.

The vulnerability exists within the code responsible for parsing a stored backup file. A 32-bit integer value, representing the size of a record, is taken from the file and used to calculate the number of bytes to read into a heap buffer. This calculation can underflow, which leads to insufficient memory being allocated. The buffer is subsequently overfilled leading to an exploitable condition.

ANALYSIS

Exploitation of this vulnerability results in the execution of arbitrary code with the privileges of the SQL Server. SQL Server 2005 runs under the "NETWORK SERVICE" account, which is similar to an unprivileged user account.

The target function can be run by any user with access to query the database. This attack could also be conducted anonymously through a Web application if it contained an SQL Injection vulnerability.

For the server to load the corrupted backup file, an attacker would have to supply a path to a remote file using either SMB or WebDAV.

DETECTION

iDefense confirmed the existence of this vulnerability in Microsoft SQL Server 2005 Service Pack 2 Hot Fix 4. Additional tests against SQL Server 2005 without any updates suggest it is also vulnerable. Previous versions are also suspected to be vulnerable.

WORKAROUND

iDefense is currently unaware of any direct workaround for this issue. Administrators can disable SMB and WebDAV support on affected SQL Servers to prevent access to remote files.

VENDOR RESPONSE

Microsoft has officially addressed this vulnerability with Security Bulletin MS08-040. For more information, consult their bulletin at the following URL.

http://www.microsoft.com/technet/security/bulletin/ms08-040.mspx

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2008-0107 to this issue. This is a candidate for inclusion in the CVE list (http://cve.mitre.org/), which standardizes names for security problems.

DISCLOSURE TIMELINE

12/06/2007 Initial vendor notification
12/06/2007 Initial vendor response
07/08/2008 Coordinated public disclosure

CREDIT

This vulnerability was reported to iDefense by Brett Moore, from Insomnia Security, brett.moore@insomniasec.com www.insomniasec.com

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LEGAL NOTICES

Copyright © 2008 Verisign, Inc.

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