Improper Certificate Validation in GnuTLS - CVE-2026-42013

Vulnerability identifier: #VU128575

CSH Severity: Medium

CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-42013

CWE-ID: CWE-295

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to bypass certificate hostname validation.

The vulnerability exists due to improper certificate validation in certificate Subject Alternative Name and Common Name hostname checking when validating certificates with oversized Subject Alternative Names. A remote attacker can present a specially crafted certificate to bypass certificate hostname validation.

GnuTLS
SUSE Linux Enterprise Server 15 SP5
Debian Linux
SUSE Linux Enterprise Server 12 SP5 LTSS Extended
SUSE Linux Enterprise Server 15 SP4
SUSE Linux Enterprise Server 15 SP6
SUSE Linux Enterprise Server for SAP Applications 15
SUSE Linux Enterprise Server 15
SUSE Linux Enterprise High Performance Computing 15
SUSE Linux Enterprise High Performance Computing ESPOS 15
SUSE Linux Enterprise High Performance Computing LTSS 15
SUSE Linux Enterprise Server 12
SUSE Linux Enterprise Server for SAP Applications 12
SUSE Linux Enterprise Desktop 15
SUSE Linux Enterprise Real Time 15
SUSE Linux Enterprise Micro
SUSE Linux Enterprise Micro for Rancher
Anolis OS
Red Hat Enterprise Linux Server - AUS
Red Hat Enterprise Linux for x86_64 - Extended Update Support
Red Hat Enterprise Linux for IBM z Systems - Extended Update Support
Red Hat Enterprise Linux for Power, little endian - Extended Update Support
Red Hat Enterprise Linux for ARM 64 - Extended Update Support
Basesystem Module
openSUSE Leap
Ubuntu
openEuler
Red Hat Enterprise Linux Server for Power LE - Update Services for SAP Solutions
libgnutls-openssl27
libgnutls-devel
libgnutls28-32bit
libgnutls28
gnutls-debugsource
libgnutls-openssl-devel
libgnutlsxx-devel
libgnutls28-debuginfo
libgnutls-openssl27-debuginfo
libgnutls28-debuginfo-32bit
gnutls-debuginfo
gnutls
gnutls (Red Hat package)
gnutls28 (Ubuntu package)
libgnutls30-32bit
libgnutls30-debuginfo
libgnutls30
libgnutls30-debuginfo-32bit
gnutls-help
gnutls-utils
gnutls-devel
gnutls-c++
gnutls-dane
libgnutls30-64bit
libgnutls-devel-64bit
libgnutls30-hmac-64bit
libgnutls30-64bit-debuginfo
libgnutls30-hmac-32bit
libgnutls-devel-32bit
libgnutls30-32bit-debuginfo
libgnutlsxx28-debuginfo
libgnutls30-hmac
gnutls-guile-debuginfo
gnutls-guile
libgnutlsxx28
gnutls28 (Debian package)
gnutls-doc
libgnutlsxx30
libgnutlsxx30-debuginfo
libtasn1 (Red Hat package)

Install security update from vendor's website.

GnuTLS - update to 3.8.13
libgnutls-openssl27 - update to 3.3.27-3.21.1
libgnutls-devel - addressed in versions 3.3.27-3.21.1, 3.7.3-150400.4.59.1, 3.8.3-150600.4.20.1
libgnutls28-32bit - update to 3.3.27-3.21.1
libgnutls28 - update to 3.3.27-3.21.1
gnutls-debugsource - addressed in versions 3.3.27-3.21.1, 3.4.17-8.26.1, 3.7.3-150400.4.59.1, 3.7.3-150400.24.2, 3.8.3-150600.4.20.1
libgnutls-openssl-devel - update to 3.3.27-3.21.1
libgnutlsxx-devel - addressed in versions 3.3.27-3.21.1, 3.7.3-150400.4.59.1, 3.8.3-150600.4.20.1
libgnutls28-debuginfo - update to 3.3.27-3.21.1
libgnutls-openssl27-debuginfo - update to 3.3.27-3.21.1
libgnutls28-debuginfo-32bit - update to 3.3.27-3.21.1
gnutls-debuginfo - addressed in versions 3.3.27-3.21.1, 3.7.3-150400.4.59.1, 3.7.3-150400.24.2, 3.8.3-150600.4.20.1
gnutls - addressed in versions 3.3.27-3.21.1, 3.7.3-150400.4.59.1, 3.7.3-150400.24.2, 3.8.3-150600.4.20.1
gnutls (Red Hat package) - addressed in versions 3.3.29-9.el7_9.2, 3.6.14-10.el8_4.1, 3.6.16-5.el8_6.5, 3.7.6-21.el9_2.7, 3.8.9-9.el10_0.19
gnutls28 (Ubuntu package) - addressed in versions 3.4.10-4ubuntu1.9+esm4, 3.5.18-1ubuntu1.6+esm4, 3.6.13-2ubuntu1.12+esm3, 3.7.3-4ubuntu1.9, 3.8.3-1.1ubuntu3.6, 3.8.9-3ubuntu2.2, 3.8.12-2ubuntu1.1
libgnutls30-32bit - addressed in versions 3.4.17-8.26.1, 3.7.3-150400.4.59.1, 3.8.3-150600.4.20.1
libgnutls30-debuginfo - addressed in versions 3.4.17-8.26.1, 3.7.3-150400.4.59.1, 3.7.3-150400.24.2, 3.8.3-150600.4.20.1
libgnutls30 - addressed in versions 3.4.17-8.26.1, 3.7.3-150400.4.59.1, 3.7.3-150400.24.2, 3.8.3-150600.4.20.1
libgnutls30-debuginfo-32bit - update to 3.4.17-8.26.1
gnutls-help - addressed in versions 3.6.14-22, 3.7.2-23, 3.8.2-14
gnutls-utils - addressed in versions 3.6.14-22, 3.7.2-23, 3.8.2-14
gnutls-devel - addressed in versions 3.6.14-22, 3.7.2-23, 3.8.2-14
gnutls-debugsource - addressed in versions 3.6.14-22, 3.7.2-23, 3.8.2-14
gnutls-debuginfo - addressed in versions 3.6.14-22, 3.7.2-23, 3.8.2-14
gnutls - addressed in versions 3.6.14-22, 3.7.2-23, 3.8.2-14
gnutls-c++ - addressed in versions 3.6.16-8.0.2, 3.8.2-9
gnutls - addressed in versions 3.6.16-8.0.2, 3.8.2-9
gnutls-dane - addressed in versions 3.6.16-8.0.2, 3.8.2-9
gnutls-devel - addressed in versions 3.6.16-8.0.2, 3.8.2-9
gnutls-utils - addressed in versions 3.6.16-8.0.2, 3.8.2-9
libgnutls30-64bit - addressed in versions 3.7.3-150400.4.59.1, 3.8.3-150600.4.20.1
libgnutls-devel-64bit - addressed in versions 3.7.3-150400.4.59.1, 3.8.3-150600.4.20.1
libgnutls30-hmac-64bit - update to 3.7.3-150400.4.59.1
libgnutls30-64bit-debuginfo - addressed in versions 3.7.3-150400.4.59.1, 3.8.3-150600.4.20.1
libgnutls30-hmac-32bit - update to 3.7.3-150400.4.59.1
libgnutls-devel-32bit - addressed in versions 3.7.3-150400.4.59.1, 3.8.3-150600.4.20.1
libgnutls30-32bit-debuginfo - addressed in versions 3.7.3-150400.4.59.1, 3.8.3-150600.4.20.1
libgnutlsxx28-debuginfo - update to 3.7.3-150400.4.59.1
libgnutls30-hmac - addressed in versions 3.7.3-150400.4.59.1, 3.7.3-150400.24.2
gnutls-guile-debuginfo - update to 3.7.3-150400.4.59.1
gnutls-guile - update to 3.7.3-150400.4.59.1
libgnutlsxx28 - update to 3.7.3-150400.4.59.1
gnutls28 (Debian package) - addressed in versions 3.7.9-2+deb12u7, 3.8.9-3+deb13u4
gnutls-doc - update to 3.8.2-9
gnutls-dane - update to 3.8.2-14
libgnutlsxx30 - update to 3.8.3-150600.4.20.1
libgnutlsxx30-debuginfo - update to 3.8.3-150600.4.20.1
libtasn1 (Red Hat package) - addressed in versions 4.13-3.el8_4.1, 4.13-3.el8_6.2

• https://www.gnutls.org/security-new.html#GNUTLS-SA-2026-04-29-8
• https://gitlab.com/gnutls/gnutls/-/issues/1825

• Multiple vulnerabilities in GnuTLS
• openEuler 24.03 LTS SP3 update for gnutls
• openEuler 24.03 LTS SP1 update for gnutls
• openEuler 24.03 LTS update for gnutls
• Debian update for gnutls28
• Ubuntu update for gnutls28
• openEuler 22.03 LTS SP4 update for gnutls
• openEuler 20.03 LTS SP4 update for gnutls
• SUSE update for gnutls
• SUSE update for gnutls
• Anolis OS update for gnutls
• Anolis OS update for gnutls
• Red Hat Enterprise Linux 10 update for gnutls
• Red Hat Enterprise Linux 8 update for multiple packages
• Red Hat Enterprise Linux 8 update for multiple packages
• SUSE update for gnutls
• SUSE update for gnutls
• SUSE update for gnutls
• Ubuntu update for gnutls28
• Red Hat Enterprise Linux 9 update for gnutls
• Red Hat Enterprise Linux 7 Extended Lifecycle Support update for gnutls