CVE-2014-3556

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.

Published: 2014-12-29 Last update: 2026-05-06 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2014-3556 is rated High Risk (66.4/100): CVSS Medium severity, with high exploitation likelihood (EPSS 48.17%, 98th percentile). EPSS ranks this CVE among the most likely to be exploited in the near term. EPSS rose +27.59% over the last day, indicating growing attacker interest. High exploitation likelihood—assess exposure and prioritize remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2014-3556

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-03-04 20.58% 48.17% +27.59%
2 2026-03-01 48.17% 20.58% -27.59%
3 2026-02-04 — 48.17% —

Full EPSS history (39 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2014-3556

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.8 2.0 MEDIUM
AV:N/AC:M/Au:N/C:P/I:P/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:M)
Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:P)
Partial availability impact.
 8.6 6.4 [email protected]

Weakness enumeration for CVE-2014-3556

OS Trackers for CVE-2014-3556

vendor priority summary link
debian not yet assigned CVE-2014-3556 not yet assigned priority: Debian including 1 source packages (nginx), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2014-3556
redhat medium — https://access.redhat.com/security/cve/CVE-2014-3556
suse medium — https://www.suse.com/security/cve/CVE-2014-3556/
ubuntu medium CVE-2014-3556 medium priority: Ubuntu including 1 source packages (nginx), 4 status rows across 4 suites (lucid, precise, trusty, upstream): not-affected 2, ignored 1, released 1. https://ubuntu.com/security/CVE-2014-3556

Affected software / configurations for CVE-2014-3556

Vendor Product Version Raw CPE
f5 nginx >= 1.5.6, < 1.6.1 cpe:2.3:a:f5:nginx:*:*:*:*:*:*:*:*
f5 nginx >= 1.7.0, < 1.7.4 cpe:2.3:a:f5:nginx:*:*:*:*:*:*:*:*

References for CVE-2014-3556

cvelogic Threat Intelligence