In Bouncy Castle for Java prior to version 1.85, the S/MIME validator uses the signingTime presented by the signer as part of the certificate path validation. This flaw means an attacker can deliver a signature with a manipulated signingTime, which the validator accepts. The result is a bypass of certificate life‑time checks, potentially allowing certificates that should be expired or revoked to be treated as valid. The weakness falls under CWE-345, a flaw that allows an attacker to manipulate a signed data field to subvert validation logic.

Affected products are Bouncy Castle for Java (BC-JAVA) before 1.85, Bouncy Castle for Java LTS (BC-LTS-JAVA) before 2.73.12, and Bouncy Castle for Java FIPS (BC-FJA) before specific releases: 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). All these products are distributed by the Legion of the Bouncy Castle Inc.

The CVSS score of 8.7 indicates a high severity. EPSS information is not available, so the exact likelihood of exploitation cannot be quantified, but the vulnerability is not listed in CISA's KEV catalog. Attackers can exploit the flaw by supplying an S/MIME message that contains an attacker‑crafted signingTime to influence path validation. If a vulnerable application accepts such a message, it may later trust a forged certificate chain, compromising authentication and integrity of communications.