CVE-2026-42013 Red Hat CVE debrief

Who should care

Defenders responsible for certificate validation processes, especially those using gnutls, should assess exposure in systems relying on certificate validation for secure communication.

Why it matters

A flaw in gnutls could allow a remote attacker to bypass proper certificate validation, potentially leading to spoofing or man-in-the-middle attacks. Defenders should prioritize verifying certificate validation processes, especially those using gnutls, and assess exposure in systems relying on certificate validation for secure communication.

• Potential bypass of certificate validation leading to spoofing or man-in-the-middle attacks.
• Verification of certificate validation processes is necessary to prevent potential attacks.
• Exposure assessment is required for systems relying on certificate validation for secure communication.
• Patching affected products is necessary to mitigate the vulnerability.

Technical summary

The gnutls library has a flaw where 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. The vulnerability affects systems using gnutls for certificate validation, particularly those with complex certificate validation processes or exposed to potential spoofing attacks. Defenders should prioritize verifying certificate validation processes, especially those using gnutls, and assess exposure in systems relying on certificate validation for secure communication.

Defensive priority

Defenders should prioritize verifying certificate validation processes, especially those using gnutls, and assess exposure in systems relying on certificate validation for secure communication.

Recommended defensive actions

• Verify certificate validation processes, especially those using gnutls.
• Assess exposure in systems relying on certificate validation for secure communication.
• Apply patches provided by Red Hat for affected products.
• Monitor for potential spoofing or man-in-the-middle attacks.
• Review compensating controls for exposed systems while remediation is scheduled and verified.
• Check relevant monitoring, detection, and logs for exposed assets that need extra review.
• Track exceptions, retest remediated assets, and close the item only after evidence is documented.

Evidence notes

The CVE record and NVD detail page provide information on the vulnerability. Red Hat has released several errata related to this issue, indicating affected products and providing patches. Specifically, Red Hat errata RHSA-2026:13274, RHSA-2026:20611, and RHSA-2026:20612 address this vulnerability. Defenders should verify the affected products and apply the necessary patches. The vulnerability details are based on the information available from these sources, and further verification is recommended.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.