EEYEB-20050801 Windows Embedded Open Type (EOT) Font Heap Overflow
Vulnerability

Release Date:
January 10, 2006

Date Reported:
July 31, 2005

Time to Patch:
163 Days

Severity:
High (Code Execution)

Systems Affected:
Windows ME
Windows 98
Windows NT
Windows 2000
Windows XP SP1 / SP2
Windows Server 2003 SP0 / SP1

Overview:
eEye Digital Security has discovered a vulnerability in the way Windows
uncompresses Embedded Open Type fonts that would allow the author of a
malicious web page to execute arbitrary code on the system of a user who
visits the site, at the privilege level of that user.

Embedded Open Type fonts are referenced through the use of style data,
as the following snippet illustrates:

    @font-face {
        font-family: Abysmal;
        font-style:  normal;
        font-weight: normal;
        src: url(evil.eot);

Although these fonts typically have .eot file extensions, it should be
noted that any extension may be used in order to exploit this
vulnerability.

Technical Details:
A heap overflow vulnerability exists in T2EMBED.DLL, which Internet
Explorer invokes to process EOT fonts.  The data within an EOT file is
compressed in Agfa MicroType Express format, which hosts an
LZ-compressed stream that includes a 24-bit allocation size.  This size
+ 1C00h is allocated within the function MTX_LZCOMP_UnPackMemory, but
the resulting allocation size is not validated before data is copied
into the block, allowing a malformed EOT file to cause an essentially
arbitrary-length heap buffer overflow with binary data.

Protection:
Retina Network Security Scanner has been updated to identify this
vulnerability.
Blink End-Point Protection proactively protects against this
vulnerability.

Vendor Status:
Microsoft has released a patch for this vulnerability.  The patch is
available at:
http://www.microsoft.com/technet/security/bulletin/MS06-002.mspx

References:
EEYE ID# EEYEB-20050801
OSVDB ID# 18829
CVE # CVE-2006-0010

Credit:
Fang Xing

Greetings:
eEye Research and especially Derek for all his help

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