The vulnerability resides in Bouncy Castle for Java libraries prior to version 1.85 and the LTS line before 2.73.12, where the Diffie‑Hellman key agreement routine exponentiates a peer value that has not been validated. Because the library accepts any peer‑provided DH parameters, an attacker can supply crafted values that lead to an incorrect or predictable shared secret. This can allow the attacker to recover session keys, decrypt traffic, or otherwise break confidentiality for connections that rely on the affected library.

Any Java application that uses Bouncy Castle for Java up to version 1.84 or the long‑term support build up to 2.73.11 is affected. The library is widely used in SSL/TLS stacks, secure messaging, and other cryptographic components in enterprise and open source Java projects.

The CVSS base score is 9.3, indicating a high security impact. EPSS is not available and the flaw is not listed in the CISA Known Exploited Vulnerabilities catalog. The attack vector is effectively remote, as a malicious peer can transmit the unvalidated DH parameters over a network that the application trusts. Exploitation would require the application to initiate or accept a DH key agreement session with a compromised party, which is common in many network protocols that rely on Bouncy Castle.