fix: prevent CSR extensions from overriding CA-managed key usage in c…#1436
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mitch292 merged 1 commit intoApr 17, 2026
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…opy_extensions When copy_extensions is enabled, CSR-provided X.509v3 extensions are copied into the certificate template's ExtraExtensions. Go's x509.CreateCertificate gives ExtraExtensions precedence over struct fields for the same OID, which means an attacker-crafted CSR could inject KeyUsage, ExtKeyUsage, and other security-critical extensions that silently override the signing profile's intended restrictions. Add a blocklist of CA-managed extension OIDs (KeyUsage, ExtKeyUsage, BasicConstraints, SKI, AKI, SAN, Name Constraints, CRL Distribution Points, Authority Info Access, Certificate Policies, Issuer Alt Name) that are never copied from CSR extensions. These extensions are authoritatively set by the CA's signing profile via FillTemplate and must not be overridable by a CSR submitter. Non-standard/private-use extensions continue to be copied through when copy_extensions is enabled.
jvaughan-cloudflare
approved these changes
Apr 16, 2026
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…opy_extensions
When copy_extensions is enabled, CSR-provided X.509v3 extensions are copied into the certificate template's ExtraExtensions. Go's x509.CreateCertificate gives ExtraExtensions precedence over struct fields for the same OID, which means an attacker-crafted CSR could inject KeyUsage, ExtKeyUsage, and other security-critical extensions that silently override the signing profile's intended restrictions.
Add a blocklist of CA-managed extension OIDs (KeyUsage, ExtKeyUsage, BasicConstraints, SKI, AKI, SAN, Name Constraints, CRL Distribution Points, Authority Info Access, Certificate Policies, Issuer Alt Name) that are never copied from CSR extensions. These extensions are authoritatively set by the CA's signing profile via FillTemplate and must not be overridable by a CSR submitter.
Non-standard/private-use extensions continue to be copied through when copy_extensions is enabled.