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[USN-8539-1] GnuTLS vulnerabilities

Posted on 14 July 2026
Ubuntu Security

==========================================================================Ubuntu Security Notice USN-8539-1
July 14, 2026

gnutls28 vulnerabilities
==========================================================================
A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 20.04 LTS
- Ubuntu 18.04 LTS
- Ubuntu 16.04 LTS

Summary:

Several security issues were fixed in GnuTLS.

Software Description:
- gnutls28: GNU TLS library

Details:

Haruto Kimura discovered that GnuTLS did not properly apply permitted
name constraints in certain certificate validation paths. A remote
attacker could possibly use this issue to bypass certificate validation,
leading to a machine-in-the-middle attack. (CVE-2026-42011)

Oleh Konko discovered that GnuTLS incorrectly fell back to Common Name
checks for certain URI and SRV subject alternative names. A remote
attacker could possibly use this issue to bypass certificate validation,
leading to a machine-in-the-middle attack. (CVE-2026-42012)

Haruto Kimura and Joshua Rogers discovered that GnuTLS incorrectly fell
back to Common Name checks when subject alternative names were
oversized. A remote attacker could possibly use this issue to bypass
certificate validation, leading to a machine-in-the-middle attack.
(CVE-2026-42013)

Luigino Camastra and Joshua Rogers discovered that GnuTLS had a
use-after-free issue when changing PKCS#11 token security officer PINs
in certain cases. An attacker could possibly use this issue to cause
GnuTLS to crash, resulting in a denial of service, or execute arbitrary
code. (CVE-2026-42014)

Zou Dikai discovered that GnuTLS did not properly validate PKCS#12 bag
sizes in certain cases. An attacker could possibly use this issue to
cause GnuTLS to crash, resulting in a denial of service, or execute
arbitrary code. (CVE-2026-42015)

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 20.04 LTS
libgnutls30 3.6.13-2ubuntu1.12+esm3
Available with Ubuntu Pro

Ubuntu 18.04 LTS
libgnutls30 3.5.18-1ubuntu1.6+esm4
Available with Ubuntu Pro

Ubuntu 16.04 LTS
libgnutls30 3.4.10-4ubuntu1.9+esm4
Available with Ubuntu Pro

In general, a standard system update will make all the necessary changes.

References:
https://ubuntu.com/security/notices/USN-8539-1
CVE-2026-42011, CVE-2026-42012, CVE-2026-42013, CVE-2026-42014,
CVE-2026-42015

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