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SquirrelMail G/PGP Plugin gpg_check_sign_pgp_mime() 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_check_sign_pgp_mime() defined in gpg_hook_functions.php. A call is made to exec() with unfiltered user-supplied data as demonstrated in the following piece of code:

 $command = "echo -n "$messageSignedText" | $path_to_gpg --batch  --no-tty --homedir $gpg_key_dir --verify ". $detachedSignatureFilename."- 2>&1"; 
 if ($debug) echo "gpg command: ".$command.""; exec($command, $results, $returnval); 

The '$messageSignedText' variable from above contains the stripped e-mail message.

ANALYSIS

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

Exploitation of this vulnerability occurs when a target webmail user opens a malicious e-mail message. As such the vulnerability can be exploited by any attacker who can convince a target user to open a malicious message.

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.

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():

 $messageSignedText= escapeshellarg($messageSignedText); 

Please note that this is an unofficial source patch, but should be sufficient as a workaround.

VENDOR RESPONSE

The maintainers of the SquirrelMail G/PGP plug-in have not responded to repeated inquires regarding this vulnerability. Versions since 2.1devbuild12Sep06 appear to include a fix for this problem. This problem is not present in the recent 2.1 release made on July 7th, 2007.

CVE INFORMATION

A Mitre Corp. Common Vulnerabilities and Exposures (CVE) number has not been assigned yet.

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.