iDEFENSE Security Advisory 08.12.04a: Adobe Acrobat Reader (Unix) Shell Metacharacter Code Execution Vulnerability

[idlabs-advisories () idefense com]

Adobe Acrobat Reader (Unix) Shell Metacharacter Code Execution
Vulnerability

iDEFENSE Security Advisory 08.12.04a
www.idefense.com/application/poi/display?id=124&type=vulnerabilities
August 12, 2004

I. BACKGROUND

Adobe Acrobat Reader is a program for viewing Portable Document Format
(PDF) documents. Uuencoding is a scheme that converts 8 bit data into a
6 bit format, suitable for transmission via e-mail.

II. DESCRIPTION

Remote exploitation of an input validation error in the uudecoding
feature of Adobe Acrobat Reader (Unix) 5.0 allows an attacker to execute
arbitrary code.

The Unix and Linux versions of Adobe Acrobat Reader 5.0 automatically
attempt to convert uuencoded documents back into their original format. 
The vulnerability specifically exists in the failure of Acrobat Reader 
to check for the backtick shell metacharacter in the filename before 
executing a command with a shell. This allows a maliciously constructed 
filename to execute arbitrary programs.

III. ANALYSIS

Successful exploitation allows attackers to execute arbitrary code under
the privileges of the user who opened the malicious document with a
vulnerable version of Adobe Acrobat Reader. PDF documents are frequently
exchanged via e-mail and in combination with a social engineering attack
allows attackers to remotely exploit this vulnerability.

IV. DETECTION

Adobe Acrobat Reader (Unix) versions 5.05 and 5.06 have been confirmed
vulnerable; earlier versions that call the uudecode utility are also
thought to be vulnerable.

V. WORKAROUNDS

Users must be wary when opening attachments from untrusted sources
whether they are executable or not. As the Windows version of Acrobat
Reader is not vulnerable to the described vulnerability it can be safely
used to open PDF documents suspected to be maliciously designed to
exploit this issue.

VI. VENDOR RESPONSE

iDEFENSE brought this vulnerability to the attention of the vendor
according to the publicized timeline. However, the vendor appears to
have silently fixed this vulnerability without coordinating public
disclosure of the issue. Moreover, the vendor does not appear to have
publicly posted details of the security fix to inform clients of the
risks posed by unpatched versions of the software. While it is not clear
exactly when the vulnerability was patched, iDEFENSE has tested Adobe
Acrobat Reader (UNIX) 5.0.9, which appears to be patched against this
vulnerability.

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CAN-2004-0630 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

03/30/2004   Initial vendor notification
04/05/2004   iDEFENSE clients notified
04/06/2004   Initial vendor response
05/19/2004   Date stamp on patched binary
08/12/2004   Public disclosure

IX. CREDIT

Greg MacManus (iDEFENSE Labs) is credited with this discovery.

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X. LEGAL NOTICES

Copyright (c) 2004 iDEFENSE, Inc.

Permission is granted for the redistribution of this alert
electronically. It may not be edited in any way without the express
written consent of iDEFENSE. If you wish to reprint the whole or any
part of this alert in any other medium other than electronically, please
email customerservice () idefense com for permission.

Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
of the information constitutes acceptance for use in an AS IS condition.
There are no warranties with regard to this information. Neither the
author nor the publisher accepts any liability for any direct, indirect,
or consequential loss or damage arising from use of, or reliance on,
this information.

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