What’s Vulnerable › Vulnerabilities

CVE-2026-33810: Case-sensitive excludedSubtrees name constraints cause Auth Bypass in crypto/x509

• Severity: high (CVSS 8.2 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: 2026-04-08 · updated 2026-09-18
• Weakness: CWE-295

Description

When verifying a certificate chain containing excluded DNS constraints, these constraints are not correctly applied to wildcard DNS SANs which use a different case than the constraint. This only affects validation of otherwise trusted certificate chains, issued by a root CA in the VerifyOptions.Roots CertPool, or in the system certificate pool.

Affected products

• Go: from 1.26.0 before 1.26.2 — fixed in 1.26.2
• Go Stdlib: from 1.26.0-0 before 1.26.2 — fixed in 1.26.2

How to fix

Upgrade to a fixed version: Go 1.26.2; Go Stdlib 1.26.2. Check the vendor advisory for mitigations.

References

• https://go.dev/cl/763763
• https://go.dev/issue/78332
• https://groups.google.com/g/golang-announce/c/0uYbvbPZRWU
• https://pkg.go.dev/vuln/GO-2026-4866
• http://www.openwall.com/lists/oss-security/2026/04/19/4
• http://www.openwall.com/lists/oss-security/2026/04/20/1
• https://access.redhat.com/errata/RHSA-2026:10155
• https://access.redhat.com/errata/RHSA-2026:10158
• https://access.redhat.com/errata/RHSA-2026:13545
• https://access.redhat.com/errata/RHSA-2026:14391
• https://access.redhat.com/errata/RHSA-2026:19135
• https://access.redhat.com/errata/RHSA-2026:19144

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