CVE-2026-63571: legion of the bouncy castle inc. bc-csharp

Vulnerability summary

CVE-2026-63571 is a high (CVSS 8.7) vulnerability in legion of the bouncy castle inc. bc-csharp. EPSS estimates a 0.17% chance of exploitation in the next 30 days, higher than 5.9% of scored vulnerabilities.

Timeline

1. 02-10-2026
   PublishedVulnerability first disclosed.
2. 02-10-2026
   Last modifiedVulnerability information updated.

Description

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.

• CWE-347Improper Verification of Cryptographic SignatureThe product does not verify, or incorrectly verifies, the cryptographic signature for data.