CVE-2026-63571: CWE-347 Improper Verification of Cryptographic Signature in Legion of the Bouncy Castle Inc. 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.
AI Analysis
Technical Summary
The vulnerability CVE-2026-63571 in bc-csharp prior to 2.7.0 is due to improper verification of cryptographic signatures in the attribute certificate path validator components (PkixAttrCertPathValidator and PkixAttrCertPathBuilder). Specifically, the validation steps check the holder and issuer certification paths, validity period, extensions, and revocation status but fail to verify the attribute certificate's signature against the issuer's public key. This allows a remote attacker to present a forged X.509 attribute certificate that names a trusted attribute authority as its issuer but is not actually signed by it, potentially gaining unauthorized privileges granted by the application based on these attributes.
Potential Impact
An attacker can exploit this vulnerability to have a forged X.509 attribute certificate accepted as valid by affected applications. This can lead to unauthorized acquisition of roles or privileges that the application grants based on attribute certificates. The vulnerability affects only applications that use the vulnerable classes for attribute certificate validation. There are no known exploits in the wild at this time.
Mitigation Recommendations
A fix is available in bc-csharp version 2.7.0 and later. Users should upgrade to version 2.7.0 or newer to remediate this vulnerability. Since the vendor advisory indicates the issue is fixed in 2.7.0, upgrading is the recommended mitigation.
CVE-2026-63571: CWE-347 Improper Verification of Cryptographic Signature in Legion of the Bouncy Castle Inc. bc-csharp
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 v4.0
Score 8.7high
Affected software
Legion of the Bouncy Castle Inc.
bc-csharp
pkg:nuget/BouncyCastle.CryptographyRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The vulnerability CVE-2026-63571 in bc-csharp prior to 2.7.0 is due to improper verification of cryptographic signatures in the attribute certificate path validator components (PkixAttrCertPathValidator and PkixAttrCertPathBuilder). Specifically, the validation steps check the holder and issuer certification paths, validity period, extensions, and revocation status but fail to verify the attribute certificate's signature against the issuer's public key. This allows a remote attacker to present a forged X.509 attribute certificate that names a trusted attribute authority as its issuer but is not actually signed by it, potentially gaining unauthorized privileges granted by the application based on these attributes.
Potential Impact
An attacker can exploit this vulnerability to have a forged X.509 attribute certificate accepted as valid by affected applications. This can lead to unauthorized acquisition of roles or privileges that the application grants based on attribute certificates. The vulnerability affects only applications that use the vulnerable classes for attribute certificate validation. There are no known exploits in the wild at this time.
Mitigation Recommendations
A fix is available in bc-csharp version 2.7.0 and later. Users should upgrade to version 2.7.0 or newer to remediate this vulnerability. Since the vendor advisory indicates the issue is fixed in 2.7.0, upgrading is the recommended mitigation.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- bcorg
- Date Reserved
- 2026-07-16T23:50:45.118Z
- Cvss Version
- 4.0
- State
- PUBLISHED
Threat ID: 6abf5de5a43b0b3b8988e87a
Added to database: 10/02/2026, 07:31:49 UTC
Last enriched: 10/02/2026, 07:46:38 UTC
Last updated: 10/02/2026, 22:45:56 UTC
Views: 11
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