---
id: CVE-2026-63571
title: >-
  Improper verification of cryptographic signature in the attribute certificate
  path validator (PkixAttrCertPathValidator, also used by
  PkixAttrCertPathBuilder) in Legion of the Bouncy Castle Inc
summary: >-
  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 att…
severity: high
cvss: 8.7
cvssVector: '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'
cwe:
  - CWE-347
vendor: Legion of the Bouncy Castle Inc.
product: BouncyCastle.Cryptography
affected:
  - BouncyCastle.Cryptography < 2.7.0
published: '2026-10-02'
updated: '2026-10-02'
sourceUpdated: '2026-10-02T08:17:01.993'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-63571'
references:
  - url: >-
      https://github.com/bcgit/bc-csharp/commit/c08f65e1ed7b92a10776220ed9c047f47c264725
    label: 91579145-5d7b-4cc5-b925-a0262ff19630
  - url: 'https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63571'
    label: 91579145-5d7b-4cc5-b925-a0262ff19630
tags:
  - nvd
  - cve.org
cvssSource: cna
ingestedAt: '2026-10-02T08:14:06.229Z'
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.