{"id":"CVE-2026-63569","revision":"bf93f9474a304ca4ade9ec9a0e631853","records":[{"revision":"bf93f9474a304ca4ade9ec9a0e631853","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-63569","aliases":[],"title":"MTI/A0 DHAgreement does not validate the peer's ephemeral value","description":"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.","state":0,"publishedAt":"2026-10-02T07:00:23.526+00:00","modifiedAt":"2026-10-02T19:07:59.005+00:00","affected":[{"ecosystem":"https://www.nuget.org/packages/BouncyCastle.Cryptography","name":"BouncyCastle.Cryptography","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"vendor\": \"Legion of the Bouncy Castle Inc.\",\n                    \"product\": \"bc-csharp\",\n                    \"collectionURL\": \"https://www.nuget.org/packages/BouncyCastle.Cryptography\",\n                    \"packageName\": \"BouncyCastle.Cryptography\",\n                    \"repo\": \"https://github.com/bcgit/bc-csharp\",\n                    \"programFiles\": [\n                        \"crypto/src/crypto/agreement/DHAgreement.cs\"\n                    ],\n                    \"versions\": [\n                        {\n                            \"status\": \"affected\",\n                            \"version\": \"0\",\n                            \"lessThan\": \"2.7.0\",\n                            \"versionType\": \"semver\"\n                        }\n                    ],\n                    \"defaultStatus\": \"unaffected\"\n                }"}],"metrics":[{"system":"CVSS 4.0","vector":"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","score":9.1,"severity":"CRITICAL"}],"references":["https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63569","https://github.com/bcgit/bc-csharp/commit/fe236ad207c5960eeae1ebb6560c783a3bb5b692"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-63569","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-63569","identifiers":["CVE-2026-63569"]},"retained":false,"historicalAffected":[]}],"coverage":[]}