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.
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.
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.
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