# CVE-2026-42013: Gnutls: gnutls: certificate validation bypass due to oversized subject alternative name

Status: published. Published: 2026-05-26. Updated: 2026-11-11.

A flaw was found in gnutls. When validating certificates, an oversized Subject Alternative Name (SAN) could cause the validation process to incorrectly fall back to checking the Common Name (CN) field. This could allow a remote attacker to bypass proper certificate validation, potentially leading to spoofing or man-in-the-middle attacks.

## Remediation

- workaround: Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability. (source: CNA: redhat)

## Affected products and versions

-  /  (gnutls): 0 (affected). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 10 (gnutls): ≥ 0:3.8.10-4.el10_2; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 10.0 Extended Update Support (gnutls): ≥ 0:3.8.9-9.el10_0.19; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 7 Extended Lifecycle Support (gnutls): ≥ 0:3.3.29-9.el7_9.2; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8 (gnutls): ≥ 0:3.6.16-8.el8_10.6; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support (gnutls): ≥ 0:3.6.14-10.el8_4.1; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support (libtasn1): ≥ 0:4.13-3.el8_4.1; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On (gnutls): ≥ 0:3.6.14-10.el8_4.1; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On (libtasn1): ≥ 0:4.13-3.el8_4.1; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support (gnutls): ≥ 0:3.6.16-5.el8_6.5; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support (libtasn1): ≥ 0:4.13-3.el8_6.2; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8.6 Extended Update Support Long-Life Add-On (gnutls): ≥ 0:3.6.16-5.el8_6.5; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8.6 Extended Update Support Long-Life Add-On (libtasn1): ≥ 0:4.13-3.el8_6.2; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8.8 Telecommunications Update Service (gnutls): ≥ 0:3.6.16-7.el8_8.4; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8.8 Telecommunications Update Service (libtasn1): ≥ 0:4.13-4.el8_8.1; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8.8 Update Services for SAP Solutions (gnutls): ≥ 0:3.6.16-7.el8_8.4; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 8.8 Update Services for SAP Solutions (libtasn1): ≥ 0:4.13-4.el8_8.1; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9 (gnutls): ≥ 0:3.8.10-4.el9_8; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions (gnutls): ≥ 0:3.7.6-21.el9_2.7; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9.4 Update Services for SAP Solutions (gnutls): ≥ 0:3.8.3-4.el9_4.6; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 9.6 Extended Update Support (gnutls): ≥ 0:3.8.3-6.el9_6.4; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 4.12 (openshift/ose-rhel-coreos-8): ≥ 412.86.202608241157-0; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 4.13 (openshift/ose-rhel-coreos-9): ≥ 413.92.202611041925-0; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 4.14 (openshift/ose-rhel-coreos-9): ≥ 414.92.202611040941-0; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 4.16 (openshift/ose-rhel-coreos-9): ≥ 416.94.202608150307-0; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 4.17 (openshift/ose-rhel-coreos-9): ≥ 417.94.202608250221-0; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 4.18 (openshift/ose-rhel-coreos-9): ≥ 418.94.202608142238-0; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 4.19 (openshift/ose-rhel-coreos-9): ≥ 4.19.9.6.202607151909-0; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 4.20 (openshift/ose-rhel-coreos-9): ≥ 4.20.9.6.202610242033-0; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 4.21 (openshift/ose-rhel-coreos-9): ≥ 4.21.9.6.202610241345-0; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 4.22 (openshift/ose-rhel-coreos-9): ≥ 4.22.9.8.202610241758-0; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Cert Manager support for Red Hat OpenShift release 1.17 (cert-manager/jetstack-cert-manager-acmesolver-rhel9): ≥ 1791371080; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Cert Manager support for Red Hat OpenShift release 1.17 (cert-manager/jetstack-cert-manager-rhel9): ≥ 1791371069; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Cert Manager support for Red Hat OpenShift release 1.17 (cert-manager/cert-manager-operator-rhel9): ≥ 1791788287; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Cert Manager support for Red Hat OpenShift release 1.17 (cert-manager/cert-manager-operator-bundle): ≥ 1791970484; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Cert Manager support for Red Hat OpenShift release 1.18 (cert-manager/jetstack-cert-manager-acmesolver-rhel9): ≥ 1791459707; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Cert Manager support for Red Hat OpenShift release 1.18 (cert-manager/jetstack-cert-manager-rhel9): ≥ 1791459711; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Cert Manager support for Red Hat OpenShift release 1.18 (cert-manager/cert-manager-istio-csr-rhel9): ≥ 1791459759; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Cert Manager support for Red Hat OpenShift release 1.18 (cert-manager/cert-manager-operator-rhel9): ≥ 1789029076; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Cert Manager support for Red Hat OpenShift release 1.18 (cert-manager/cert-manager-operator-bundle): ≥ 1791966259; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Cert Manager support for Red Hat OpenShift release 1.20 (cert-manager/cert-manager-trust-manager-rhel9): ≥ 1790598593; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Discovery 2 (discovery/discovery-server-rhel9): ≥ 1782159791; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Discovery 2 (discovery/discovery-ui-rhel9): ≥ 1782166952; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Hardened Images (gnutls-main): ≥ 3.8.13-1.hum1; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat OpenShift AI 3.4 (rhai/base-image-neuron-rhel9): ≥ 1790703542; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Update Infrastructure 5 (rhui5/cds-rhel9): ≥ 1781525684; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Update Infrastructure 5 (rhui5/haproxy-rhel9): ≥ 1781525671; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Update Infrastructure 5 (rhui5/installer-rhel9): ≥ 1781525693; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Update Infrastructure 5 (rhui5/rhua-rhel9): ≥ 1781525739; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Update Infrastructure 5 (rhui5/cds-kubernetes-tp-rhel9): ≥ 1787241211; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Update Infrastructure 5 (rhui5/installer-tp-rhel9): ≥ 1787135742; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Update Infrastructure 5 (rhui5/rhua-tp-rhel9): ≥ 1787241260; < * (unaffected, rpm). Source: CNA: redhat
- Red Hat / Red Hat Enterprise Linux 6 (gnutls): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 4 (openshift4/ose-hypershift-rhel9): Version range not reported. Source: CNA: redhat
- Red Hat / Red Hat OpenShift Container Platform 5 (openshift/ose-rhel-coreos-9): Version range not reported. Source: CNA: redhat

## Severity and prioritization

- CVSS 3.1: 8.2 (high); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:N; source: CNA: redhat

- CVSS 3.1: 8.2 (high); CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:N; source: NVD: secalert@redhat.com

- CISA KEV: No listing in collected sources

- EPSS: 0.42% as of 2026-11-10; percentile 36.89%

- SSVC: exploitation none; automatable yes; technical impact partial; source ADP: CISA-ADP

- Weaknesses: CWE-295

## Exploit evidence

No exploit evidence in collected sources. This is not proof of no exploitation.

## References

- https://access.redhat.com/errata/RHSA-2026:13274 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:20611 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:20612 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:20613 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:26319 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:26409 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:29197 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:30004 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:30849 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:30850 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:32962 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:33125 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:40762 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:41921 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:43575 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:56853 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:57483 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:58981 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:59831 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:60019 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:72502 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:74674 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82304 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82322 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82347 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82354 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82372 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82857 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:82888 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:89197 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:89232 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:89333 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:95508 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/errata/RHSA-2026:95745 (CNA: redhat; vendor-advisory, x_refsource_REDHAT)

- https://access.redhat.com/security/cve/CVE-2026-42013 (CNA: redhat; vdb-entry, x_refsource_REDHAT)

- https://bugzilla.redhat.com/show_bug.cgi?id=2467448 (CNA: redhat; issue-tracking, x_refsource_REDHAT)

- https://www.gnutls.org/security-new.html#GNUTLS-SA-2026-04-29-8 (CNA: redhat)

- https://access.redhat.com/errata/RHSA-2026:13274 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:20611 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:20612 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:20613 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:26319 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:26409 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:29197 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:30004 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:30849 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:30850 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:32962 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:33125 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:40762 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:41921 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:43575 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:56853 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:57483 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:58981 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:59831 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:60019 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:72502 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:74674 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:82304 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:82322 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:82347 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:82354 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:82372 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:82857 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:82888 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:89197 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:89232 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:89333 (secalert@redhat.com)

- https://access.redhat.com/errata/RHSA-2026:95508 (secalert@redhat.com)

- https://access.redhat.com/security/cve/CVE-2026-42013 (secalert@redhat.com)

- https://bugzilla.redhat.com/show_bug.cgi?id=2467448 (secalert@redhat.com)

- https://www.gnutls.org/security-new.html#GNUTLS-SA-2026-04-29-8 (secalert@redhat.com)

## Provenance

- CNA: redhat: https://www.cve.org/CVERecord?id=CVE-2026-42013; retrieved 2026-11-11; source updated 2026-11-11

- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-42013; retrieved 2026-11-10; source updated 2026-11-09

- FIRST EPSS: https://api.first.org/data/v1/epss?cve=CVE-2026-42013; retrieved 2026-11-11; source updated Not reported

Revision: acafd7d3293d9ecc5be87c48ced7becd965231bb80f37dfffb4aa2a2112d45ae

Canonical: https://y2.dev/cve/CVE-2026-42013

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