Impact

The isMail transport in PHPMailer before 5.2.20 might allow remote attackers to pass extra parameters to the mail command and consequently execute arbitrary code by leveraging improper interaction between the escapeshellarg function and internal escaping performed in the mail function in PHP. NOTE: this vulnerability exists because of an incorrect fix for CVE-2016-10033.

This issue really emphasises that it's worth avoiding the built-in PHP mail() function entirely.

Patches

Fixed in 5.2.20

Workarounds

Send via SMTP to localhost instead of calling the mail() function.

References

https://nvd.nist.gov/vuln/detail/CVE-2016-10045
See also https://nvd.nist.gov/vuln/detail/CVE-2016-10033

For more information

If you have any questions or comments about this advisory:

• Open a private issue in the PHPMailer project