[UNIX] SquirrelMail S/MIME Plugin Command Injection

From: SecuriTeam (support_at_securiteam.com)
Date: 02/17/05

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Date: 17 Feb 2005 19:36:01 +0200

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      SquirrelMail S/MIME Plugin Command Injection
    ------------------------------------------------------------------------

    SUMMARY

    Squirrelmail S/MIME plugin 'enables the viewing of S/MIME-signed messages
    of the MIME "multipart/signed" format'. 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.

    DETAILS

    Vulnerable Systems:
     * SquirrelMail S/MIME plugin version 0.5 and prior

    Immune Systems:
     *

    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.

    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.

    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);

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

    Disclosure Timeline:
    09/22/2004 - Initial vendor notification
    09/22/2004 - Initial vendor response
    02/07/2005 - Coordinated public disclosure

    ADDITIONAL INFORMATION

    The information has been provided by
    <mailto:customerservice@idefense.com> iDEFENSE.
    The original article can be found at:
    <http://www.idefense.com/application/poi/display?id=191&type=vulnerabilities> http://www.idefense.com/application/poi/display?id=191&type=vulnerabilities

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