CVE-2014-3556: F5 Nginx

Medium severity, CVSS 6.8. EPSS: 7.8% chance of exploitation in the next 30 days.

The STARTTLS implementation in mail/ngx_mail_smtp_handler.c in the SMTP proxy in nginx 1.5.x and 1.6.x before 1.6.1 and 1.7.x before 1.7.4 does not properly restrict I/O buffering, which allows man-in-the-middle attackers to insert commands into encrypted SMTP sessions by sending a cleartext command that is processed after TLS is in place, related to a "plaintext command injection" attack, a similar issue to CVE-2011-0411.

Affected products

• F5 Nginx: from 1.5.6, before 1.6.1 (fixed in 1.6.1); from 1.7.0, before 1.7.4 (fixed in 1.7.4)

Published 2014-12-29. Last modified 2026-06-17.