Security Advisory: ZF2016-04

ZF2016-04: Potential remote code execution in zend-mail via Sendmail adapter

When using the zend-mail component to send email via the Zend\Mail\Transport\Sendmail transport, a malicious user may be able to inject arbitrary parameters to the system sendmail program. The attack is performed by providing additional quote characters within an address; when unsanitized, they can be interpreted as additional command line arguments, leading to the vulnerability.

The following example demonstrates injecting additional parameters to the sendmail binary via the From address:

use Zend\Mail;

$mail = new Mail\Message();
$mail->setBody('This is the text of the email.');

// inject additional parameters to sendmail command line
$mail->setFrom('"AAA\" params injection"@domain', 'Sender\'s name');

$mail->addTo('hacker@localhost', 'Name of recipient');
$mail->setSubject('TestSubject');

$transport = new Mail\Transport\Sendmail();
$transport->send($mail);

The attack works because zend-mail filters the email addresses using the RFC 3696 specification, where the string "AAA\" params injection"@domain is considered a valid address. This validation is provided using the zend-validator component with the following parameters:

Zend\Validator\EmailAddress(
    Zend\Validator\Hostname::ALLOW_DNS | Zend\Validator\Hostname::ALLOW_LOCAL
)

The above accepts local domain with any string specified by double quotes as the local part. While this is valid per RFC 3696, due to the fact that sender email addresses are provided to the sendmail binary via the command line, they create the vulnerability described above.

Action Taken

To fix the issue, we added a transport-specific email filter for the From header in the Sendmail transport adapter. The filter checks for the sequence \" in the local part of the email From address.

$from = $headers->get('From');
if ($from) {
    foreach ($from->getAddressList() as $address) {
        if (preg_match('/\\\"/', $address->getEmail())) {
            throw new Exception\RuntimeException("Potential code injection in From header");
        }
    }
}

The patch resolving the vulnerability is available in:

• zend-mail, starting in version 2.7.2
• zend-mail, 2.4.11
• Zend Framework, 2.4.11

Zend Framework 2.5 and 3.0 versions will receive the update automatically, as executing composer update in projects using these versions will update to zend-mail 2.7.2+.

Acknowledgments

The Zend Framework team thanks the following for identifying the issues and working with us to help protect its users:

• The independent security researcher Dawid Golunski, who reported the vulnerability to Beyond Security’s SecuriTeam Secure Disclosure program;
• Enrico Zimuel, who provided the patch.

Released 2016-12-20

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