---
id: CVE-2026-63576
title: >-
  Improper certificate validation in PkixNameConstraintValidator
  (ExtractHostFromURL) in Legion of the Bouncy Castle Inc
summary: >-
  Improper certificate validation in PkixNameConstraintValidator
  (ExtractHostFromURL) in Legion of the Bouncy Castle Inc. bc-csharp before
  2.7.0 allows a name-constrained subordinate CA, or anyone able to obtain
  certificates with chosen su…
severity: high
cvss: 8.2
cvssVector: 'CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N'
cwe:
  - CWE-295
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: '2026-10-02T14:44:52.247'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-63576'
references:
  - url: >-
      https://github.com/bcgit/bc-csharp/commit/f196a22bbf7765cc19b0c4f4645c74ea7ad35e09
    label: 91579145-5d7b-4cc5-b925-a0262ff19630
  - url: 'https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63576'
    label: 91579145-5d7b-4cc5-b925-a0262ff19630
tags:
  - nvd
  - cve.org
epss: 0.00218
epssPercentile: 0.11109
cvssSource: cna
ingestedAt: '2026-10-02T08:14:06.227Z'
---

## Overview

Improper certificate validation in PkixNameConstraintValidator (ExtractHostFromURL) in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a name-constrained subordinate CA, or anyone able to obtain certificates with chosen subjectAltName URIs from such a CA, to bypass permitted or excluded uniformResourceIdentifier name constraints during certification path validation via a URI whose path, query, fragment or userinfo contains characters such as '@' or ':', because the host was extracted by string slicing without first isolating the RFC 3986 authority component, so the host compared against the constraints could differ from the URI's actual host.

## Remediation

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