Vulnerability 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.
Related Weaknesses (CWE)
References
- https://github.com/bcgit/bc-csharp/commit/fe236ad207c5960eeae1ebb6560c783a3bb5b6
- https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63569
FAQ
What is CVE-2026-63569?
CVE-2026-63569 is a documented vulnerability. 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 par...
How severe is CVE-2026-63569?
CVSS scoring is not yet available for CVE-2026-63569. Check NVD for updates.
Is there a patch for CVE-2026-63569?
Check the references section above for vendor advisories and patch information. Review vendor security bulletins for remediation guidance.