Bouncycastle: In Bouncy Castle for Java before 1.85, OpenPGP CFB quick-check oracle active on symmetric/session-key paths. (CVE-2026-59640)

The vulnerability identified as CVE-2026-59640 affects Bouncy Castle for Java prior to version 1.85, including certain LTS and FIPS releases. It involves an OpenPGP CFB quick-check oracle that is active on symmetric/session-key paths, potentially allowing an attacker to gain information about cryptographic keys. The issue is present in Bouncy Castle for Java LTS versions before 2.73.12 and in Bouncy Castle for Java FIPS before bcpg-fips 1.0.13 (1.0.X series), 2.0.13 (2.0.X series), and 2.1.13 (2.1.X series). The CVSS 3.1 base score is 5.3, reflecting a medium severity with network attack vector, low attack complexity, no privileges required, no user interaction, and limited confidentiality impact.

The vulnerability allows an attacker to perform a quick-check oracle attack on OpenPGP symmetric/session-key paths, potentially leaking limited confidential information about cryptographic keys. There is no impact on integrity or availability. No known exploits are reported in the wild, reducing immediate risk but the vulnerability could be leveraged in targeted attacks.

The vendor has released fixed versions: Bouncy Castle for Java 1.85 and later, LTS 2.73.12 and later, and FIPS versions bcpg-fips 1.0.13, 2.0.13, and 2.1.13 or later. Users should upgrade to these versions to remediate the vulnerability. Patch status is confirmed by the version numbers stated. No additional mitigations are indicated by the vendor advisory.