Bouncycastle: In Bouncy Castle for Java before 1.85, S/MIME validator trusts signer-asserted signingTime for path validation. (CVE-2026-59641)

CVE-2026-59641 affects Bouncy Castle for Java versions prior to 1.85, including LTS versions before 2.73.12 and FIPS versions before bcmail-fips and bcjmail-fips 1.0.7 (1.0.X series), 2.0.7 (2.0.X series), and 2.1.7 (2.1.X series). The vulnerability arises because the S/MIME validator trusts the signer-asserted signingTime attribute for path validation, which can be manipulated. This flaw could lead to improper validation of signed messages, potentially allowing signature validation bypass or related issues. The CVSS 3.1 score is 5.3 (medium severity), with no known exploits in the wild reported.

The vulnerability impacts the integrity validation of S/MIME signed messages by trusting the signer-asserted signingTime, which could be forged. This may allow attackers to bypass or weaken signature path validation, potentially undermining trust in signed communications. There is no reported impact on confidentiality or availability, and no known active exploitation has been documented.

A fix is available in Bouncy Castle for Java version 1.85 and later, LTS version 2.73.12 and later, and FIPS versions bcmail-fips and bcjmail-fips 1.0.7, 2.0.7, and 2.1.7 or later. Users should upgrade to these fixed versions to remediate the vulnerability. Patch status is confirmed by vendor advisories. No additional mitigations are specified.