CVE-2026-63576 (GCVE-0-2026-63576)

Vulnerability from cvelistv5 – Published: 2026-10-02 07:07 – Updated: 2026-10-02 07:07
VLAI
Title
URI name constraints checked against a mis-parsed host
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 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.
Severity
8.2 (High)
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 - Improper Certificate Validation
Assigner
References
Impacted products
Vendor Product Version CPE status
Legion of the Bouncy Castle Inc. bc-csharp Affected: 0 , < 2.7.0 (semver)
guessed Create a notification for this product.
Credits
Discovered by Claude, Anthropic's AI assistant, and triaged by the Anthropic security team in collaboration with Anthropic Research.
Show details on NVD website
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "collectionURL": "https://www.nuget.org/packages/BouncyCastle.Cryptography",
          "defaultStatus": "unaffected",
          "packageName": "BouncyCastle.Cryptography",
          "product": "bc-csharp",
          "programFiles": [
            "crypto/src/pkix/PkixNameConstraintValidator.cs",
            "crypto/src/pkix/NameConstraintUtilities.cs",
            "crypto/src/pkix/NameConstraintUri.cs"
          ],
          "repo": "https://github.com/bcgit/bc-csharp",
          "vendor": "Legion of the Bouncy Castle Inc.",
          "versions": [
            {
              "lessThan": "2.7.0",
              "status": "affected",
              "version": "0",
              "versionType": "semver"
            }
          ]
        }
      ],
      "credits": [
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          "lang": "en",
          "type": "finder",
          "value": "Discovered by Claude, Anthropic\u0027s AI assistant, and triaged by the Anthropic security team in collaboration with Anthropic Research."
        }
      ],
      "descriptions": [
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              "value": "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 \u0027@\u0027 or \u0027:\u0027, 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\u0027s actual host."
            }
          ],
          "value": "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 \u0027@\u0027 or \u0027:\u0027, 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\u0027s actual host."
        }
      ],
      "impacts": [
        {
          "descriptions": [
            {
              "lang": "en",
              "value": "Integrity (bypass of permitted/excluded URI name constraints in certification path validation)"
            }
          ]
        }
      ],
      "metrics": [
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            "Recovery": "NOT_DEFINED",
            "Safety": "NOT_DEFINED",
            "attackComplexity": "LOW",
            "attackRequirements": "PRESENT",
            "attackVector": "NETWORK",
            "baseScore": 8.2,
            "baseSeverity": "HIGH",
            "exploitMaturity": "NOT_DEFINED",
            "privilegesRequired": "NONE",
            "providerUrgency": "NOT_DEFINED",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "NONE",
            "valueDensity": "NOT_DEFINED",
            "vectorString": "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",
            "version": "4.0",
            "vulnAvailabilityImpact": "NONE",
            "vulnConfidentialityImpact": "NONE",
            "vulnIntegrityImpact": "HIGH",
            "vulnerabilityResponseEffort": "NOT_DEFINED"
          },
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          "scenarios": [
            {
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              "value": "GENERAL"
            }
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      "problemTypes": [
        {
          "descriptions": [
            {
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              "description": "CWE-295 Improper Certificate Validation",
              "lang": "en",
              "type": "CWE"
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          ]
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      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-02T07:07:02.513Z",
        "orgId": "91579145-5d7b-4cc5-b925-a0262ff19630",
        "shortName": "bcorg"
      },
      "references": [
        {
          "tags": [
            "vendor-advisory"
          ],
          "url": "https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63576"
        },
        {
          "tags": [
            "patch"
          ],
          "url": "https://github.com/bcgit/bc-csharp/commit/f196a22bbf7765cc19b0c4f4645c74ea7ad35e09"
        }
      ],
      "source": {
        "discovery": "EXTERNAL"
      },
      "title": "URI name constraints checked against a mis-parsed host",
      "x_antReportIds": [
        "ANT-2026-R05HVR25"
      ],
      "x_generator": {
        "engine": "Claude Opus 5.5"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "91579145-5d7b-4cc5-b925-a0262ff19630",
    "assignerShortName": "bcorg",
    "cveId": "CVE-2026-63576",
    "datePublished": "2026-10-02T07:07:02.513Z",
    "dateReserved": "2026-07-16T23:51:51.306Z",
    "dateUpdated": "2026-10-02T07:07:02.513Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
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      "date": "2026-10-02",
      "epss": "0.00218",
      "percentile": "0.11109"
    },
    "nvd": {
      "cve": {
        "affected": [
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            "affectedData": [
              {
                "collectionURL": "https://www.nuget.org/packages/BouncyCastle.Cryptography",
                "defaultStatus": "unaffected",
                "packageName": "BouncyCastle.Cryptography",
                "product": "bc-csharp",
                "programFiles": [
                  "crypto/src/pkix/PkixNameConstraintValidator.cs",
                  "crypto/src/pkix/NameConstraintUtilities.cs",
                  "crypto/src/pkix/NameConstraintUri.cs"
                ],
                "repo": "https://github.com/bcgit/bc-csharp",
                "vendor": "Legion of the Bouncy Castle Inc.",
                "versions": [
                  {
                    "lessThan": "2.7.0",
                    "status": "affected",
                    "version": "0",
                    "versionType": "semver"
                  }
                ]
              }
            ],
            "source": "91579145-5d7b-4cc5-b925-a0262ff19630"
          }
        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "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 \u0027@\u0027 or \u0027:\u0027, 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\u0027s actual host."
          }
        ],
        "id": "CVE-2026-63576",
        "lastModified": "2026-10-02T14:44:52.247",
        "metrics": {
          "cvssMetricV40": [
            {
              "cvssData": {
                "Automatable": "NOT_DEFINED",
                "Recovery": "NOT_DEFINED",
                "Safety": "NOT_DEFINED",
                "attackComplexity": "LOW",
                "attackRequirements": "PRESENT",
                "attackVector": "NETWORK",
                "availabilityRequirement": "NOT_DEFINED",
                "baseScore": 8.2,
                "baseSeverity": "HIGH",
                "confidentialityRequirement": "NOT_DEFINED",
                "exploitMaturity": "NOT_DEFINED",
                "integrityRequirement": "NOT_DEFINED",
                "modifiedAttackComplexity": "NOT_DEFINED",
                "modifiedAttackRequirements": "NOT_DEFINED",
                "modifiedAttackVector": "NOT_DEFINED",
                "modifiedPrivilegesRequired": "NOT_DEFINED",
                "modifiedSubAvailabilityImpact": "NOT_DEFINED",
                "modifiedSubConfidentialityImpact": "NOT_DEFINED",
                "modifiedSubIntegrityImpact": "NOT_DEFINED",
                "modifiedUserInteraction": "NOT_DEFINED",
                "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
                "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
                "modifiedVulnIntegrityImpact": "NOT_DEFINED",
                "privilegesRequired": "NONE",
                "providerUrgency": "NOT_DEFINED",
                "subAvailabilityImpact": "NONE",
                "subConfidentialityImpact": "NONE",
                "subIntegrityImpact": "NONE",
                "userInteraction": "NONE",
                "valueDensity": "NOT_DEFINED",
                "vectorString": "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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
                "version": "4.0",
                "vulnAvailabilityImpact": "NONE",
                "vulnConfidentialityImpact": "NONE",
                "vulnIntegrityImpact": "HIGH",
                "vulnerabilityResponseEffort": "NOT_DEFINED"
              },
              "source": "91579145-5d7b-4cc5-b925-a0262ff19630",
              "type": "Secondary"
            }
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        "published": "2026-10-02T08:17:02.787",
        "references": [
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            "source": "91579145-5d7b-4cc5-b925-a0262ff19630",
            "url": "https://github.com/bcgit/bc-csharp/commit/f196a22bbf7765cc19b0c4f4645c74ea7ad35e09"
          },
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            "url": "https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63576"
          }
        ],
        "sourceIdentifier": "91579145-5d7b-4cc5-b925-a0262ff19630",
        "vulnStatus": "Awaiting Analysis",
        "weaknesses": [
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                "lang": "en",
                "value": "CWE-295"
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            "source": "91579145-5d7b-4cc5-b925-a0262ff19630",
            "type": "Secondary"
          }
        ]
      }
    }
  }
}



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