Bouncycastle: In Bouncy Castle for Java before 1.85, BKS keystore accepts legacy version with 16-bit integrity MAC key. (CVE-2026-59651)

The vulnerability in Bouncy Castle for Java prior to version 1.85 and LTS prior to 2.73.12 involves the BKS keystore accepting a legacy version that uses a 16-bit integrity MAC key, which is cryptographically weak. This flaw allows an attacker to compromise the integrity of the keystore data. The weakness does not impact confidentiality or availability but can lead to unauthorized modification of keystore contents. The CVSS 3.1 vector is AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N, indicating network attack vector, low attack complexity, no privileges or user interaction required, unchanged scope, no confidentiality impact, high integrity impact, and no availability impact.

An attacker can exploit this vulnerability to compromise the integrity of the BKS keystore data by leveraging the weak 16-bit MAC key. This could allow unauthorized modification of keystore contents, potentially undermining trust in cryptographic operations relying on the keystore. There is no impact on confidentiality or availability.

The vulnerability affects Bouncy Castle for Java versions before 1.85 and LTS versions before 2.73.12. Users should upgrade to version 1.85 or later, or LTS version 2.73.12 or later, where this issue is resolved. Patch status is not explicitly confirmed in the provided data, so users should verify the availability of official fixes from the vendor or distribution maintainers. No other specific mitigations are indicated.