iDefense Security Advisory 06.10.08
http://labs.idefense.com/intelligence/vulnerabilities/
Jun 10, 2008

I. 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,
and the Sun Java JRE. For more information, please see the vendor's
website at the following URL.

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

II. 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.

III. 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.

IV. DETECTION

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

V. 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.

VI. 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

VII. 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.

VIII. DISCLOSURE TIMELINE

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

IX. CREDIT

These vulnerabilities were reported to iDefense by regenrecht.

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X. LEGAL NOTICES

Copyright © 2008 iDefense, Inc.

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