How severe is CVE-2014-3556?

CVE-2014-3556 has a CVSS 2.0 base score of 6.8, rated medium severity.

Is CVE-2014-3556 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 8% (94th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2014-3556?

CVE-2014-3556 affects F5 Nginx. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2014-3556?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2014-3556 published?

CVE-2014-3556 was published on 2014-12-29 and last updated on 2026-06-17.

CVE-2014-3556

CVE-2014-3556 is a medium-severity vulnerability in F5 Nginx with a CVSS 2.0 base score of 6.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-77.

Key facts

Severity: Medium (CVSS 2.0 base score 6.8)
EPSS exploit prediction: 8% (94th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-77
Affected product: F5 Nginx
Published: 2014-12-29
Last modified: 2026-06-17

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.

Frequently asked questions

What is 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.
How severe is CVE-2014-3556?: CVE-2014-3556 has a CVSS 2.0 base score of 6.8, rated medium severity.
Is CVE-2014-3556 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 8% (94th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2014-3556?: CVE-2014-3556 affects F5 Nginx. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2014-3556?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2014-3556 published?: CVE-2014-3556 was published on 2014-12-29 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:f5:nginx:*:*:*:*:*:*:*:*

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