CVE-2025-61727: Improper application of excluded DNS name constraints when verifying wildcard names in crypto/x509

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-12-03 · updated 2026-10-18
Weakness: CWE-295

Description

An excluded subdomain constraint in a certificate chain does not restrict the usage of wildcard SANs in the leaf certificate. For example a constraint that excludes the subdomain test.example.com does not prevent a leaf certificate from claiming the SAN *.example.com.

Affected products

Go: before 1.24.11; from 1.25 before 1.25.5 — fixed in 1.24.11, 1.25.5

How to fix

Upgrade to a fixed version: Go 1.24.11, 1.25.5. Check the vendor advisory for mitigations.

References

https://go.dev/cl/723900
https://go.dev/issue/76442
https://groups.google.com/g/golang-announce/c/8FJoBkPddm4
https://pkg.go.dev/vuln/GO-2025-4175

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