{"id":"CVE-2026-63569","published":"2026-10-02T07:16:37.430","lastModified":"2026-10-02T19:16:41.913","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.","cvssScore":null,"cvssSeverity":null,"cvssVector":null,"cwes":["CWE-20"],"vendors":[],"products":[],"references":[{"url":"https://github.com/bcgit/bc-csharp/commit/fe236ad207c5960eeae1ebb6560c783a3bb5b692","tags":[]},{"url":"https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63569","tags":[]}],"exploitRefs":[{"url":"https://github.com/bcgit/bc-csharp/commit/fe236ad207c5960eeae1ebb6560c783a3bb5b692","tags":[]},{"url":"https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63569","tags":[]}],"hasPoc":true,"ai":null}