CVE-2026-63571

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 v3 7.5 HIGH

7.5^/10

CVSS v3 : HIGH

Vector :

Exploitability : 3.9 / Impact : 3.6

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact HIGH

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://github.com/bcgit/bc-csharp/commit/c08f65e1ed7b92a10776220ed9c047f47c264725	Patch
https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63571	Patch Vendor Advisory

Configurations

Configuration 1 (hide)

cpe:2.3:a:bouncycastle:bc-csharp:*:*:*:*:*:*:*:*

History

28 Oct 2026, 13:19

Type	Values Removed	Values Added
References	~~() https://github.com/bcgit/bc-csharp/commit/c08f65e1ed7b92a10776220ed9c047f47c264725 -~~	() https://github.com/bcgit/bc-csharp/commit/c08f65e1ed7b92a10776220ed9c047f47c264725 - Patch
References	~~() https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63571 -~~	() https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63571 - Patch, Vendor Advisory
CPE		cpe:2.3:a:bouncycastle:bc-csharp::::::::
First Time		Bouncycastle bc-csharp Bouncycastle
CVSS	v2 : ~~unknown~~ v3 : ~~unknown~~	v2 : unknown v3 : 7.5

02 Oct 2026, 08:17

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-10-02 08:17

Updated : 2026-10-28 13:19

NVD link : CVE-2026-63571

Mitre link : CVE-2026-63571

CVE.ORG link : CVE-2026-63571

JSON object : View

Products Affected

bouncycastle

bc-csharp

CWE

CWE-347

Improper Verification of Cryptographic Signature

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