CVE-2026-63571
Received Received - Intake

Improper Cryptographic Signature Validation in Bouncy Castle

Publication date: 2026-10-02

Last updated on: 2026-10-02

Assigner: bcorg

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.

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Meta Information

Published
2026-10-02
Last Modified
2026-10-02
Generated
2026-10-02
AI Q&A
2026-10-02
EPSS Evaluated
N/A
NVD
CVE-2026-63571
EUVD
EUVD-2026-91222

Affected Vendors & Products

Showing 3 associated CPEs
Vendor Product Version / Range
bouncy_castle bc-csharp to 2.7.0 (exc)
bouncy_castle_inc bc_csharp to 2.7.0 (exc)
bouncy_castle_inc bc_csharp 2.7.0

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-347 The product does not verify, or incorrectly verifies, the cryptographic signature for data.

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Executive Summary

This vulnerability involves improper verification of cryptographic signatures in the attribute certificate path validator (PkixAttrCertPathValidator) in Bouncy Castle's bc-csharp library before version 2.7.0. The issue allows a remote attacker to forge an X.509 attribute certificate that appears valid but was not signed by the trusted issuer. The validator checks certification paths, validity periods, extensions, and revocation status but fails to verify the attribute certificate's signature with the issuer's public key.

Detection Guidance

To detect this vulnerability, check if your system uses Bouncy Castle bc-csharp versions 2.6.2 or earlier. Inspect the library version in your application dependencies or runtime environment. If using .NET, run commands like 'dotnet list package' or check the assembly version in your project files.

Impact Analysis

If you use applications that rely on Bouncy Castle's bc-csharp library versions 2.6.2 or earlier to validate attribute certificates, an attacker could create a fraudulent certificate that grants unauthorized roles or privileges. This could lead to privilege escalation, allowing the attacker to perform actions they are not authorized for. The impact is limited to applications using these specific classes for attribute certificate validation.

Compliance Impact

This vulnerability could undermine compliance with GDPR and HIPAA by allowing unauthorized privilege escalation through forged attribute certificates. Applications relying on Bouncy Castle's validation for role or privilege assignments may grant excessive access to attackers, violating access control requirements in these regulations.

Mitigation Strategies

Upgrade to Bouncy Castle bc-csharp version 2.7.0 or later to apply the signature verification fix. If upgrading is not possible, manually verify attribute certificate signatures before processing them in your application.

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