Improper verification of cryptographic signature in the attribute certificate path validator (PkixAttrCertPathValidator, also used by PkixAttrCertPathBuilder) in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a remote attacker to have a forged X.509 attribute certificate accepted as valid, and so obtain whatever roles or privileges an application grants on the strength of its attributes, via an attribute certificate that names a trusted attribute authority as its issuer but was not signed by it, because the RFC 3281 validation steps check the holder and issuer certification paths, validity period, extensions and revocation status but never verify the attribute certificate's signature with the issuer's public key. Only applications that use these classes to validate attribute certificates are affected.
Fix
Patch, vendor advisory and mitigation references on NVD 2
- https://github.com/bcgit/bc-csharp/commit/c08f65e1ed7b92a10776220ed9c047f47c264725 Patch
- https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63571 Patch, Vendor Advisory
Every line above is quoted from NVD, CISA, Microsoft, the vendor's own advisory or DISA; nothing is generated.
Change history 1
- First seenCVSS 8.7 · bouncycastleNVD modified 2026-10-28 13:19
Affected (CPE criteria) 1
cpe:2.3:a:bouncycastle:bc-csharp:*:*:*:*:*:*:*:*