iDefense Security Advisory 07.11.07: SquirrelMail G/PGP Plugin gpg_check_sign_pgp_mime() Command Injection Vulnerability

SquirrelMail G/PGP Plugin gpg_check_sign_pgp_mime() Command Injection 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 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.

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III. 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.

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 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.

VI. 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.

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

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In addition to our free technical library, Pantek provides professional IT services to companies who utilize Open Source software: Learn more about Pantek's Technical Support offerings Place an order for 24/7/365 Technical Support here Learn more about Pantek, who we are, and what we do Chat with a Live Operator Related securityfocus.com Links bugtraq certification focus-bsd focus-ids focus-ih focus-linux focus-ms focus-sun focus-unix-other focus-virus forensics incidents libnet linux-secnews ms-secnews pen-test secpapers secprog sectools secureshell security-basics securityjobs sf-news vuln-dev webappsec Request more information about Pantek

VIII. 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

IX. CREDIT The discoverer of this vulnerability wishes to remain anonymous.

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X. LEGAL NOTICES Copyright © 2007 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 e-mail 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. Received on Wed Jul 11 18:06:22 2007