What’s Vulnerable › Vulnerabilities

CVE-2026-27138: Panic in name constraint checking for malformed certificates in crypto/x509

• Severity: medium (CVSS 5.9 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: 2026-03-06 · updated 2026-06-17
• Weakness: CWE-295

Description

Certificate verification can panic when a certificate in the chain has an empty DNS name and another certificate in the chain has excluded name constraints. This can crash programs that are either directly verifying X.509 certificate chains, or those that use TLS.

Affected products

• Go: 1.26.0
• Go Stdlib: from 1.26.0-0 before 1.26.1 — fixed in 1.26.1

How to fix

Upgrade to a fixed version: Go Stdlib 1.26.1. Check the vendor advisory for mitigations.

References

• https://go.dev/cl/752183
• https://go.dev/issue/77953
• https://groups.google.com/g/golang-announce/c/EdhZqrQ98hk
• https://pkg.go.dev/vuln/GO-2026-4600

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