CVE-2013-6422

What it is

The GnuTLS backend in libcurl 7.21.4 through 7.33.0, when disabling digital signature verification (CURLOPT_SSL_VERIFYPEER), also disables the CURLOPT_SSL_VERIFYHOST check for CN or SAN host name fields, which makes it easier for remote attackers to spoof servers and conduct man-in-the-middle (MITM) attacks.

At a glance

Exploitability

Can be exploited over the network without logging in. Limited direct impact.

Exploit odds

2.8% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2013-12-23 22:55 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 00:00 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 2.8% in the next 30 days (EPSS).
• Severity: 4.0 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2013-12-23 22:55 UTC

Last modified

2026-06-17 00:00 UTC

Exploit probability

2.8% · EPSS, next 30 days

Weakness

CWE-20 · Improper input validation

Record status

Modified

Affected

• Debian Linux 7.0
• Canonical Ubuntu Linux 12.04
• Canonical Ubuntu Linux 12.10
• Canonical Ubuntu Linux 13.04
• Canonical Ubuntu Linux 13.10
• Haxx Libcurl 7.21.4
• Haxx Libcurl 7.21.5
• Haxx Libcurl 7.21.6

Attack profile CVSS 2.0 · 4.0

Attack vector

Network

Complexity

High

Authentication

None

Confidentiality

Partial

Integrity

Partial

Availability

None

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

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