CVE-2026-6731

highCVSS 7.5covered by 2 sourcesfirst seen 2026-06-09

X.509 name constraint bypass via the Subject Common Name when treated as a DNS-type name. A certificate whose Subject CN violates an issuing CA's DNS name constraints could be accepted.

CSIRTS triage

What: This vulnerability allows for a name constraint bypass via Subject CN treated as a DNS name.
Who is affected: Deployments using X.509 certificates with affected configurations.
Urgency: Remediation is urgent due to the high severity rating of 7.5.
Action: Apply the patch for CVE-2026-6731.

AI-assisted analysis generated from the source advisory — verify against the original.

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Exploitation outlook

Low exploitation risk0.12% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 3% of all EPSS-scored CVEs.

Advisory coverage (2)

highCVE-2026-6731: X.509 name constraint bypass via the Subject Common Name when treated as a DNS-type name. A cer…nvd · 2026-06-25
highCVE-2026-6731: X.509 name constraint bypass via Subject CN treated as a DNS namemsrc · 2026-06-09

External references

NVD record for CVE-2026-6731

CVE.org record

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