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CVE-2026-63569: Product identification pending

Severity

9.1 (CRITICAL)

Affected versions

Before 2.7.0

Fixed version

2.7.0

Patch status

Patched

Published

2026-10-02T07:16:37.430

Modified

2026-10-02T07:16:37.430

Why it matters

Critical vulnerability requiring immediate validation against your environment.

Recommended admin actions

• Prioritize validation immediately due to critical CVSS severity.
• Compare installed versions against the affected version range in the advisory.

Technical summary

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.

View the official NVD record for CVE-2026-63569

CVE data is sourced from NVD/CNA records and optional enrichment. Validate against the vendor advisory before taking production action.