What’s Vulnerable › Vulnerabilities

CVE-2014-3556

• Severity: medium (CVSS 6.8 v2.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 7.8% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2014-12-29 · updated 2026-06-17
• Weakness: CWE-77

Description

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

• nginx: from 1.5.6 before 1.6.1; from 1.7.0 before 1.7.4 — fixed in 1.6.1, 1.7.4

How to fix

Upgrade to a fixed version: nginx 1.6.1, 1.7.4. Check the vendor advisory for mitigations.

References

• http://mailman.nginx.org/pipermail/nginx-announce/2014/000144.html
• http://marc.info/?l=bugtraq&m=142103967620673&w=2
• http://nginx.org/download/patch.2014.starttls.txt
• https://bugzilla.redhat.com/show_bug.cgi?id=1126891
• http://mailman.nginx.org/pipermail/nginx-announce/2014/000144.html
• http://marc.info/?l=bugtraq&m=142103967620673&w=2
• http://nginx.org/download/patch.2014.starttls.txt
• https://bugzilla.redhat.com/show_bug.cgi?id=1126891

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