iDEFENSE Security Advisory 02.07.05: SquirrelMail S/MIME Plugin Command Injection Vulnerability

SquirrelMail S/MIME Plugin Command Injection Vulnerability

iDEFENSE Security Advisory 02.07.05
www.idefense.com/application/poi/display?id=191&type=vulnerabilities
February 07, 2005

I. BACKGROUND

Squirrelmail S/MIME plugin enables the viewing of S/MIME-signed messages
of the MIME "multipart/signed" format. More information about the plugin
is available at:

    http://www.squirrelmail.org/plugin_view.php?id=54

II. DESCRIPTION

Remote exploitation of a command injection vulnerability in the
Squirrelmail S/MIME plugin allows web mail users to execute arbitrary
commands with the privileges of the web server.

The problem specifically exists due to insufficient filtering of
user-provided data in a call to exec(). The following snippet exposes
the offending area of code from viewcert.php:

    if(!isset($cert)) $cert=$_GET['cert'];
    ...
    function x509_open($cert) {
        global $cert_in_dir, $openssl;
        $lines = array();
        exec("$openssl x509 -in $cert_in_dir$cert -subject -issuer \
            -dates -serial -fingerprint -noout 2>/tmp/err", $lines);
    ...
    list ($ow, $is, $nb, $na, $sn, $fp) = x509_open($cert);

The variable '$cert' from the above snippet contains unfiltered user
supplied data and can be exploited.

III. ANALYSIS

Successful exploitation allows authenticated web mail users to execute
arbitrary commands on the underlying system with the privileges of the
web server. This can lead to further compromise and exposure of other
users' mail to the attacker.

IV. DETECTION

iDEFENSE has confirmed the existence of this vulnerability in S/MIME
plugin 0.5 and 0.4. Earlier versions are also suspected to be
vulnerable.

V. WORKAROUND

PHP provides the escapeshellarg() routine to filter data to be used as
an argument to calls such as exec() and system(). Modify the call to
exec() from:

    exec("$openssl x509 -in $cert_in_dir$cert -subject -issuer -dates \
        -serial -fingerprint -noout 2>/tmp/err", $lines);

To:

    $filtered = escapeshellarg("$cert_in_dir$cert");
    exec("$openssl x509 -in $filtered -subject -issuer -dates -serial \
        -fingerprint -noout 2>/tmp/err", $lines);

VI. VENDOR RESPONSE

The vendor has released S/MIME plugin 0.6 to address this vulnerability.
The plugin is available for download at:

   http://www.squirrelmail.org/plugin_view.php?id=54

VII. CVE INFORMATION

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

VIII. DISCLOSURE TIMELINE

09/22/2004  Initial vendor notification
09/22/2004  Initial vendor response
02/07/2005  Coordinated public disclosure

IX. CREDIT

Karol Wiesek is credited with this discovery.

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X. LEGAL NOTICES

Copyright (c) 2005 iDEFENSE, Inc.

Permission is granted for the redistribution of this alert
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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.