CVE-2026-63569

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.

CVSS v3 6.5 MEDIUM

6.5^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 2.8 / Impact : 3.6

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required LOW

User Interaction NONE

Confidentiality Impact HIGH

Integrity Impact NONE

Availability Impact NONE

Scope UNCHANGED

References

Link	Resource
https://github.com/bcgit/bc-csharp/commit/fe236ad207c5960eeae1ebb6560c783a3bb5b692	Patch
https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63569	Patch Vendor Advisory

Configurations

Configuration 1 (hide)

cpe:2.3:a:bouncycastle:bc-csharp:*:*:*:*:*:*:*:*

History

28 Oct 2026, 14:58

Type	Values Removed	Values Added
CVSS	v2 : ~~unknown~~ v3 : ~~unknown~~	v2 : unknown v3 : 6.5
First Time		Bouncycastle bc-csharp Bouncycastle
References	~~() https://github.com/bcgit/bc-csharp/commit/fe236ad207c5960eeae1ebb6560c783a3bb5b692 -~~	() https://github.com/bcgit/bc-csharp/commit/fe236ad207c5960eeae1ebb6560c783a3bb5b692 - Patch
References	~~() https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63569 -~~	() https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63569 - Patch, Vendor Advisory
CPE		cpe:2.3:a:bouncycastle:bc-csharp::::::::

02 Oct 2026, 07:16

Type	Values Removed	Values Added
New CVE

Information

Published : 2026-10-02 07:16

Updated : 2026-10-28 14:58

NVD link : CVE-2026-63569

Mitre link : CVE-2026-63569

CVE.ORG link : CVE-2026-63569

JSON object : View

Products Affected

bouncycastle

bc-csharp

CWE

CWE-20

Improper Input Validation

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