CVEvulnerability
CVE-2026-63569
9.1 CRITICAL
Official page ↗
- Status
- Analyzed
- Published
- 2026-10-02
- Last modified
- 2026-10-28
- Assigner
- 91579145-5d7b-4cc5-b925-a0262ff19630
- CVSS 4.0 (91579145-5d7b-4cc5-b925-a0262ff19630)
- 9.1 CRITICAL — 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
- CVSS 3.1 ([email protected])
- 6.5 MEDIUM — CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
- Weaknesses
- CWE-20
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.
Affected configurations
• bouncycastle bc-csharp (< 2.7.0)
Related
Weakness · CWE (1)
- CWE-20 Improper Input Validation weakness