{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "extracted_events": [
              {
                "introduced": "0"
              },
              {
                "fixed": "2.7.0"
              }
            ],
            "source": [
              "DESCRIPTION",
              "REFERENCES"
            ]
          },
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "4007498b13582d90ee1eda5d9920c324428b98b3"
            },
            {
              "fixed": "fe236ad207c5960eeae1ebb6560c783a3bb5b692"
            }
          ],
          "repo": "https://github.com/bcgit/bc-csharp",
          "type": "GIT"
        }
      ]
    }
  ],
  "database_specific": {
    "cna_assigner": "bcorg",
    "cwe_ids": [
      "CWE-20"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63569.json"
  },
  "details": "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.",
  "id": "CVE-2026-63569",
  "modified": "2026-10-04T02:30:58.061461844Z",
  "published": "2026-10-02T07:00:23.526Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://www.nuget.org/packages/BouncyCastle.Cryptography"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/63xxx/CVE-2026-63569.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63569"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-63569"
    },
    {
      "type": "FIX",
      "url": "https://github.com/bcgit/bc-csharp/commit/fe236ad207c5960eeae1ebb6560c783a3bb5b692"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/bcgit/bc-csharp"
    }
  ],
  "schema_version": "1.9.0",
  "severity": [
    {
      "score": "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "MTI/A0 DHAgreement does not validate the peer's ephemeral value"
}