Public Vulnerability Reports

Multiple Vendor FreeType2 Multiple Heap Overflow Vulnerabilities

10.06.08

BACKGROUND

FreeType2 is an open source library for parsing fonts that is used by many applications. This includes projects such as X.Org, Second Life, GD2, and OpenJDK. For more information, please see the vendor's website at the following URL.

http://freetype.sourceforge.net/freetype2/

DESCRIPTION

Remote exploitation of multiple heap overflow vulnerabilities in the FreeType2 library, as included in various vendors' operating systems, could allow an attacker to execute arbitrary code with the privileges of the affected application.

Two vulnerabilities exist within the code responsible for parsing font files.

The first vulnerability occurs when parsing Printer Font Binary (PFB) format font files. PFB files contain various data structures, some of which are stored in a tabular format. When parsing tables, the code doesn't correctly validate a value used as an array index into a heap buffer. The calculation contains an off-by-one error, which can result in a heap overflow.

The second vulnerability occurs when parsing TrueType Font (TTF) font files. TrueType font files contain "font programs" that are executed in a TrueType virtual machine. One of the instructions in the instruction set is 'SHC', which is used to shift a contour in the font by a specified value. When parsing this instruction, the code doesn't correctly validate an array index, which leads to an off-by-one heap overflow.

ANALYSIS

Exploitation of these vulnerabilities results in the execution of arbitrary code with the privileges of the application using the library. Since FreeType2 is a library and not a standalone application, the exploitation vector will vary. iDefense Labs verified that local privilege escalation was possible via the X.Org Xserver.

DETECTION

iDefense has confirmed the existence of these vulnerabilities in FreeType2 version 2.3.5. Previous versions may also be affected.

WORKAROUND

iDefense is currently unaware of any workarounds for these issues. Changing the permissions on the freetype.so library may not always be effective since applications that run with root privileges are not restricted by file permissions.

VENDOR RESPONSE

The FreeType maintainers addressed these vulnerabilities with the release of version 2.3.6. For more information, refer to the release notes at the following URL.

http://sourceforge.net/project/shownotes.php?group_id=3157&release_id=605780

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2008-1808 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

06/03/2008 Initial vendor notification
06/04/2008 Initial vendor response
06/10/2008 Coordinated public disclosure

CREDIT

These vulnerabilities were reported to iDefense by regenrecht.

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LEGAL NOTICES

Copyright © 2008 Verisign, Inc.

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