Bouncy Castle bc-csharp up to 2.6.x DHAgreement.CalculateAgreement input validation

Summaryinfo

A vulnerability, which was classified as critical, was found in Bouncy Castle bc-csharp up to 2.6.x. Affected by this issue is the function DHAgreement.CalculateAgreement. The manipulation results in input validation. This vulnerability is cataloged as CVE-2026-63569. The attack may be launched remotely. There is no exploit available. You should upgrade the affected component.

Detailsinfo

A vulnerability classified as critical has been found in Bouncy Castle bc-csharp up to 2.6.x. Affected is the function DHAgreement.CalculateAgreement. The manipulation with an unknown input leads to a input validation vulnerability. CWE is classifying the issue as CWE-20. The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is available at github.com. This vulnerability is traded as CVE-2026-63569 since 07/17/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. Technical details are known, but there is no available exploit.

Upgrading to version 2.7.0 eliminates this vulnerability.

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Productinfo

Vendor

• Bouncy Castle

Name

• bc-csharp

Version

• 2.0
• 2.1
• 2.2
• 2.3
• 2.4
• 2.5
• 2.6

CPE 2.3info

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CPE 2.2info

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