CVE-2026-63569

{
  "id": "CVE-2026-63569",
  "sourceIdentifier": "91579145-5d7b-4cc5-b925-a0262ff19630",
  "published": "2026-10-02T07:16:37.430",
  "lastModified": "2026-10-28T14:58:49.057",
  "vulnStatus": "Analyzed",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Improper input validation in DHAgreement.CalculateAgreement (MTI/A0 two-pass Diffie-Hellman) in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows an on-path attacker to make the local party compute an agreed value the attacker already knows, defeating the key authentication MTI/A0 is meant to provide. It also allows a malicious peer to learn the local static private key modulo the small factors of p-1, and to recover it entirely in groups with many such factors. The attack uses a crafted out-of-range or small-order ephemeral value, and works because that value is raised to the static private key without the range and subgroup-membership checks applied to DH public keys. Only applications that call DHAgreement directly are affected."
    }
  ],
  "affected": [
    {
      "source": "91579145-5d7b-4cc5-b925-a0262ff19630",
      "affectedData": [
        {
          "vendor": "Legion of the Bouncy Castle Inc.",
          "product": "bc-csharp",
          "defaultStatus": "unaffected",
          "collectionURL": "https://www.nuget.org/packages/BouncyCastle.Cryptography",
          "packageName": "BouncyCastle.Cryptography",
          "programFiles": [
            "crypto/src/crypto/agreement/DHAgreement.cs"
          ],
          "repo": "https://github.com/bcgit/bc-csharp",
          "versions": [
            {
              "version": "0",
              "lessThan": "2.7.0",
              "versionType": "semver",
              "status": "affected"
            }
          ]
        }
      ]
    }
  ],
  "metrics": {
    "cvssMetricV40": [
      {
        "source": "91579145-5d7b-4cc5-b925-a0262ff19630",
        "type": "Secondary",
        "cvssData": {
          "version": "4.0",
          "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/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",
          "baseScore": 9.1,
          "baseSeverity": "CRITICAL",
          "attackVector": "NETWORK",
          "attackComplexity": "LOW",
          "attackRequirements": "PRESENT",
          "privilegesRequired": "NONE",
          "userInteraction": "NONE",
          "vulnConfidentialityImpact": "HIGH",
          "vulnIntegrityImpact": "HIGH",
          "vulnAvailabilityImpact": "NONE",
          "subConfidentialityImpact": "NONE",
          "subIntegrityImpact": "NONE",
          "subAvailabilityImpact": "NONE",
          "exploitMaturity": "NOT_DEFINED",
          "confidentialityRequirement": "NOT_DEFINED",
          "integrityRequirement": "NOT_DEFINED",
          "availabilityRequirement": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
          "modifiedAttackRequirements": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedUserInteraction": "NOT_DEFINED",
          "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
          "modifiedVulnIntegrityImpact": "NOT_DEFINED",
          "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedSubIntegrityImpact": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "Safety": "NOT_DEFINED",
          "Automatable": "NOT_DEFINED",
          "Recovery": "NOT_DEFINED",
          "valueDensity": "NOT_DEFINED",
          "vulnerabilityResponseEffort": "NOT_DEFINED",
          "providerUrgency": "NOT_DEFINED"
        }
      }
    ],
    "cvssMetricV31": [
      {
        "source": "[email protected]",
        "type": "Primary",
        "cvssData": {
          "version": "3.1",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N",
          "baseScore": 6.5,
          "baseSeverity": "MEDIUM",
          "attackVector": "NETWORK",
          "attackComplexity": "LOW",
          "privilegesRequired": "LOW",
          "userInteraction": "NONE",
          "scope": "UNCHANGED",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "NONE",
          "availabilityImpact": "NONE"
        },
        "exploitabilityScore": 2.8,
        "impactScore": 3.6
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "timestamp": "2026-10-02T19:06:30.758087Z",
          "id": "CVE-2026-63569",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "total"
            }
          ],
          "role": "CISA Coordinator",
          "version": "2.0.3"
        }
      }
    ]
  },
  "weaknesses": [
    {
      "source": "91579145-5d7b-4cc5-b925-a0262ff19630",
      "type": "Secondary",
      "description": [
        {
          "lang": "en",
          "value": "CWE-20"
        }
      ]
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "operator": "OR",
          "negate": false,
          "cpeMatch": [
            {
              "vulnerable": true,
              "criteria": "cpe:2.3:a:bouncycastle:bc-csharp:*:*:*:*:*:*:*:*",
              "versionEndExcluding": "2.7.0",
              "matchCriteriaId": "21A715E8-41BE-47EB-833D-07B9908CCF31"
            }
          ]
        }
      ]
    }
  ],
  "references": [
    {
      "url": "https://github.com/bcgit/bc-csharp/commit/fe236ad207c5960eeae1ebb6560c783a3bb5b692",
      "source": "91579145-5d7b-4cc5-b925-a0262ff19630",
      "tags": [
        "Patch"
      ]
    },
    {
      "url": "https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63569",
      "source": "91579145-5d7b-4cc5-b925-a0262ff19630",
      "tags": [
        "Patch",
        "Vendor Advisory"
      ]
    }
  ]
}