SquirrelMail G/PGP Plugin gpg_help.php Local File Inclusion Vulnerability

iDefense Security Advisory 07.11.07
http://labs.idefense.com/intelligence/vulnerabilities/ 
Jul 11, 2007

I. BACKGROUND

The SquirrelMail G/PGP Encrpytion Plugin is a general purpose
encryption, decryption, and digital signature plug-in for SquirrelMail
that implements the OpenPGP standard using GPG. More information is
available at the following URL.

http://www.squirrelmail.org/plugin_view.php?id=153 

II. DESCRIPTION

Remote exploitation of a local file inclusion vulnerability in version
2.0 of the SquirrelMail G/PGP Plugin could allow an authenticated
webmail user to execute arbitrary PHP code under the security context
of the running web server.

Version 2.0 of the SquirrelMail G/PGP Plugin contains an implementation
flaw in the way it includes certain files. Specifically, the
'gpg_help.php' and 'gpg_help_base.php' files will include local files
that are supplied via the 'help' HTTP GET request parameter. An excerpt
from the code follows:

    68  // Help body text is inserted here via GET parameter
    69  require_once (SM_PATH.'plugins/gpg/help/' . $_GET['help'] );

By using directory traversal specifiers, an attacker can trivially cause
files stored on the Web server to be parsed as PHP code.

III. ANALYSIS

Exploitation could allow an attacker to include an arbitrary local file
on the affected host.

Due to the lack of input validation on $GET_['help'], directory
traversal specifiers could be utilized to parse any file on the system
as PHP code.

IV. DETECTION

iDefense has confirmed the existence of this vulnerability in version
2.0 of the G/PGP Encryption Plugin for SquirrelMail. It is suspected
that earlier versions of the plug-in are also affected.

V. WORKAROUND

iDefense is unaware of any available workarounds for this vulnerability.

VI. VENDOR RESPONSE

The maintainers of the SquirrelMail G/PGP plug-in have not responded to
repeated inquires regarding this vulnerability. Versions since
gpg.2.1devbuild14Jun07 appear to include a fix for this problem. This
problem is not present in the recent 2.1 release made on July 7th,
2007.

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
name CVE-2006-4169 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

08/16/2006  Initial vendor notification
10/06/2006  Second vendor notification
02/16/2007  Third vendor notification
07/11/2007  Public disclosure

IX. CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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X. LEGAL NOTICES

Copyright =A9 2007 iDefense, Inc.

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