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

Severity: high (CVSS 8.2 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-05-26 · updated 2026-10-30
Weakness: CWE-295

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.

Affected products

[UNKNOWN] gnutls: 0
Red Hat Cert Manager support for Red Hat OpenShift release 1.17: all versions — fixed in 1791371080
Red Hat Cert Manager support for Red Hat OpenShift release 1.18: all versions — fixed in 1791459707
Red Hat Cert Manager support for Red Hat OpenShift release 1.20: all versions — fixed in 1790598593
Red Hat OpenShift Container Platform 4.18: all versions — fixed in 418.94.202608142238-0
Red Hat Discovery 2: all versions — fixed in 1782159791
Red Hat Enterprise Linux 10: all versions — fixed in 0:3.8.10-4.el10_2
Red Hat Enterprise Linux 10.0 Extended Update Support: all versions — fixed in 0:3.8.9-9.el10_0.19
Red Hat Enterprise Linux 7 Extended Lifecycle Support: all versions — fixed in 0:3.3.29-9.el7_9.2
Red Hat Enterprise Linux 8: all versions — fixed in 0:3.6.16-8.el8_10.6
Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support: all versions — fixed in 0:3.6.14-10.el8_4.1
Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On: all versions — fixed in 0:3.6.14-10.el8_4.1
Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support: all versions — fixed in 0:3.6.16-5.el8_6.5
Red Hat Enterprise Linux 8.6 Extended Update Support Long-Life Add-On: all versions — fixed in 0:3.6.16-5.el8_6.5
Red Hat Enterprise Linux 8.8 Telecommunications Update Service: all versions — fixed in 0:3.6.16-7.el8_8.4
Red Hat Enterprise Linux 8.8 Update Services for SAP Solutions: all versions — fixed in 0:3.6.16-7.el8_8.4
Red Hat Enterprise Linux 9: all versions — fixed in 0:3.8.10-4.el9_8
Red Hat Enterprise Linux 9.2 Update Services for SAP Solutions: all versions — fixed in 0:3.7.6-21.el9_2.7
Red Hat Enterprise Linux 9.4 Update Services for SAP Solutions: all versions — fixed in 0:3.8.3-4.el9_4.6
Red Hat Enterprise Linux 9.6 Extended Update Support: all versions — fixed in 0:3.8.3-6.el9_6.4
Red Hat Hardened Images: all versions — fixed in 3.8.13-1.hum1
Red Hat OpenShift AI 3.4: all versions — fixed in 1790703542
Red Hat OpenShift Container Platform 4.12: all versions — fixed in 412.86.202608241157-0
Red Hat OpenShift Container Platform 4.16: all versions — fixed in 416.94.202608150307-0
Red Hat OpenShift Container Platform 4.17: all versions — fixed in 417.94.202608250221-0
Red Hat OpenShift Container Platform 4.19: all versions — fixed in 4.19.9.6.202607151909-0
Red Hat OpenShift Container Platform 4.20: all versions — fixed in 4.20.9.6.202610242033-0
Red Hat OpenShift Container Platform 4.21: all versions — fixed in 4.21.9.6.202610241345-0
Red Hat OpenShift Container Platform 4.22: all versions — fixed in 4.22.9.8.202610241758-0
Red Hat OpenShift Container Platform 5: all versions

How to fix

Upgrade to a fixed version: Red Hat Cert Manager support for Red Hat OpenShift release 1.17 1791371080; Red Hat Cert Manager support for Red Hat OpenShift release 1.18 1791459707; Red Hat Cert Manager support for Red Hat OpenShift release 1.20 1790598593; Red Hat OpenShift Container Platform 4.18 418.94.202608142238-0; Red Hat Discovery 2 1782159791; Red Hat Enterprise Linux 10 0:3.8.10-4.el10_2; Red Hat Enterprise Linux 10.0 Extended Update Support 0:3.8.9-9.el10_0.19; Red Hat Enterprise Linux 7 Extended Lifecycle Support 0:3.3.29-9.el7_9.2; Red Hat Enterprise Linux 8 0:3.6.16-8.el8_10.6; Red Hat Enterprise Linux 8.4 Advanced Mission Critical Update Support 0:3.6.14-10.el8_4.1; Red Hat Enterprise Linux 8.4 Extended Update Support Long-Life Add-On 0:3.6.14-10.el8_4.1; Red Hat Enterprise Linux 8.6 Advanced Mission Critical Update Support 0:3.6.16-5.el8_6.5. Check the vendor advisory for mitigations.

References

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