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Vulnerability record · CVE-2026-63571 · published 2 October 2026

CVE-2026-63571: Bouncycastle bc-csharp improper verification of cryptographic signature vulnerability

Bouncycastle · Bc Csharp

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.

8.7 CVSS 4.0 High EPSS 0.14% · top 96.5% CWE-347 · Improper verification of cryptographic signature
8.7CVSS 4.0 base score
0.14%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
2References
28 Oct 2026Last modified by NVD

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.

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/bcgit/bc-csharp/commit/c08f65e1ed7b92a10776220ed9c047f47c264725 Patch
https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63571 PatchVendor Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

9.1CVE-2026-63569Bouncycastle bc-csharp improper input validation vulnerabilityImproper input validation in DHAgreement.CalculateAgreement (MTI/A0 two-pass Diffie-Hellman) in Legion of the Bouncy Castle Inc. bc-csharp before 2.7…EPSS 0.33%8.7CVE-2026-63574Bouncycastle bc-csharp vulnerabilityMemory allocation with excessive size value in the OpenPGP signature and user attribute subpacket parsers (SignatureSubpacketsParser.ReadPacket, User…EPSS 0.43%8.7CVE-2026-103604Bouncycastle bc-csharp vulnerabilityInefficient algorithmic complexity in X.509 distinguished name string conversion (X509Name.ToString and IetfUtilities.ValueToString) in Legion of the…EPSS 0.32%8.7CVE-2026-103600Bouncycastle bc-csharp vulnerabilityUncontrolled recursion in the ASN.1 parser (Asn1InputStream, Asn1StreamParser) in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a re…EPSS 0.36%8.7CVE-2026-103603Bouncycastle bc-csharp vulnerabilityMemory allocation with excessive size value in the HSS/LMS signature code (HssPublicKeyParameters, HssSignature) in Legion of the Bouncy Castle Inc. …EPSS 0.52%8.7CVE-2026-63568Bouncycastle bc-csharp allocation without limits vulnerabilityAllocation of resources without limits or throttling in the CMP/CRMF password-based MAC verifier (PKMacBuilder) in Legion of the Bouncy Castle Inc. b…EPSS 0.36%8.7CVE-2026-63566Bouncycastle bc-csharp vulnerabilityMemory allocation with excessive size value in the DTLS handshake reassembly (DtlsReliableHandshake, DtlsReassembler) in Legion of the Bouncy Castle …EPSS 0.43%8.7CVE-2026-16000Bouncycastle bc-csharp vulnerabilityMissing cryptographic step in the DSTU 7624 CCM mode implementation (KCcmBlockCipher) in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allo…EPSS 0.22%

Source: NIST National Vulnerability Database (record CVE-2026-63571), CISA KEV, FIRST EPSS (scores of 2026-11-14). This page is refreshed as NVD updates the record.