Adobe Acrobat Reader UnixAppOpenFilePerform() Buffer Overflow
Vulnerability

iDEFENSE Security Advisory 07.05.05
www.idefense.com/application/poi/display?id=279&type=vulnerabilities
July 05, 2005

I. BACKGROUND

Adobe Acrobat Reader is a program for viewing Portable Document Format
(PDF) documents. More information is available at the following site:

   http://www.adobe.com/products/acrobat/readermain.html

II. DESCRIPTION

Remote exploitation of a buffer overflow in Adobe Acrobat Reader for 
Unix could allow an attacker to execute arbitrary code. 

The vulnerability specifically exists in the function 
UnixAppOpenFilePerform(). This routine is called by Acrobat Reader while

opening a document containing a /Filespec tag. Within this routine, 
sprintf is used to copy user-supplied data into a fixed-sized stack 
buffer. This leads to a stack based overflow and the execution of 
arbitrary code. The following demonstrates what the overflow looks like 
in a debugger: 

#0  0x41414141 in ?? ()
(gdb) i r ebx
ebx            0xbfffef54       -1073746092
(gdb) x/x 0xbfffef54
0xbfffef54:     0x40404040
(gdb) 

As shown, EIP is easily controllable; ebx also points to the 4 bytes 
before the EIP overwrite in a controlled buffer. This allows remote 
exploitation without having to know stack addresses, as an attacker can 
craft an exploit to return to a jmp ebx or call ebx instruction.

III. ANALYSIS

Successful exploitation allows an attacker to execute arbitrary code 
under the privileges of the local user. Remote exploitation is possible 
via e-mail attachment or link to the maliciously crafted PDF document. 
The impact of this vulnerability is lessened by the fact that two error 
messages appear before exploitation is successful; however, closing 
these windows does not prevent exploitation from occurring.

IV. DETECTION

iDEFENSE has confirmed the existence of this vulnerability in Adobe 
Acrobat Reader version 5.0.9 for Unix and Adobe Acrobat Reader version 
5.0.10 for Unix. Adobe Acrobat for Windows is not affected. Adobe
Acrobat 7.0 for Unix is not affected.

V. WORKAROUND

User awareness is the best defense against this class of attack. Users 
should be aware of the existence of such attacks and proceed with 
caution when following links from suspicious or unsolicited e-mail. 
Users should consider using an unaffected version of Adobe Acrobat, such

as Acrobat 7.0

VI. VENDOR RESPONSE

Adobe has addressed this issue in the following security advisory:

   http://www.adobe.com/support/techdocs/329083.html

Adobe is recommending the following steps for remediation:

 -- If you use Adobe Reader 5.0.9 or 5.0.10 on Linux or Solaris,
download Adobe Reader 7.0 at
www.adobe.com/products/acrobat/readstep2.html.

 -- If you use Adobe Reader 5.0.9 or 5.0.10 on IBM-AIX or HP-UX,
download Adobe Reader 5.0.11 at
www.adobe.com/products/acrobat/readstep2.html.

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CAN-2005-1625 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

05/12/2005  Initial vendor notification
05/12/2005  Initial vendor response
07/05/2005  Public disclosure

IX. CREDIT

iDEFENSE Labs is credited with this discovery.

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X. LEGAL NOTICES

Copyright (c) 2005 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.