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SquirrelMail G/PGP Plugin gpg_recv_key() Command Injection Vulnerability

07.11.07

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

DESCRIPTION

Remote exploitation of a command injection vulnerability in the G/PGP Encrpytion Plugin for The SquirrelMail Project Team's SquirrelMail webmail package allows attackers to execute arbitrary commands with the privileges of the underlying web server.

The problem specifically exists within the function gpg_recv_key() defined in gpg_key_functions.php. A call is made to exec() with unfiltered user-supplied data as demonstrated in the following piece of code:

 $command = "$path_to_gpg --batch --no-tty --homedir $gpg_key_dir  --keyserver hkp://$keyserver --recv-key $searchkeyid 2>&1"; [...] exec($command, $output, $returnval); 

The aforementioned '$keyserver' variable is supplied in the POST data to the gpg_options.php script. The attacker must have a valid authenticated session to exploit this vulnerability.

ANALYSIS

Exploitation of the described vulnerability allows authenticated remote attackers to execute arbitrary commands with the privileges of the underlying web server.

This vulnerability could be exploited by webmail users to gain shell access on the target server and potentially further compromise the system with local privilege escalation vulnerabilities.

DETECTION

iDefense has confirmed the existence of this vulnerability in the latest version of the G/PGP Encryption Plugin for SquirrelMail, version 2.1. Furthermore, this vulnerability has been confirmed to exist as early as version 2.0. Other versions may be affected.

WORKAROUND

Disable the G/PGP Plugin if it is not required. Alternatively, add the following line above the initialization of the '$command' variable just prior to the call to exec():

 $keyserver = escapeshellarg($keyserver); 

Please note that this is an unofficial source patch, but should be sufficient as a workaround until an official patch is released from the vendor.

VENDOR RESPONSE

The maintainers of the SquirrelMail G/PGP plug-in have not responded to repeated inquires regarding this vulnerability. As such, it remains unpatched, even in the most current release made on July 7th, 2007.

CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2005-1924 to this issue. This is a candidate for inclusion in the CVE list (http://cve.mitre.org/), which standardizes names for security problems.

DISCLOSURE TIMELINE

10/27/2005 Initial vendor notification
10/27/2005 Initial vendor response
03/02/2006 Second vendor notification
02/16/2007 Third vendor notification
07/11/2007 Public disclosure

CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

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LEGAL NOTICES

Copyright © 2007 Verisign, Inc.

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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.