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CVE-2026-59641: S/MIME validator trusts signer-asserted signingTime for path validation

• Severity: medium (CVSS 5.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-03 · updated 2026-08-28
• Weakness: CWE-345

Description

In Bouncy Castle for Java before 1.85, S/MIME validator trusts signer-asserted signingTime for path validation. This issue also affects Bouncy Castle for Java LTS before 2.73.12, and Bouncy Castle for Java FIPS (BC-FJA) 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).

Affected products

• Legion of the Bouncy Castle Inc. BC-JAVA: before 1.85 — fixed in 1.85
• Bouncycastle Bcjmail-Fips: before 1.0.7; from 2.0.5 before 2.0.7; from 2.1.6 before 2.1.7 — fixed in 1.0.7, 2.0.7, 2.1.7
• Bouncycastle Bcmail-Fips: before 1.0.7; from 2.0.5 before 2.0.7; from 2.1.6 before 2.1.7 — fixed in 1.0.7, 2.0.7, 2.1.7
• Legion of the Bouncy Castle Inc. Bouncy Castle for Java LTS: through 2.73.11

How to fix

Upgrade to a fixed version: Legion of the Bouncy Castle Inc. BC-JAVA 1.85; Bouncycastle Bcjmail-Fips 1.0.7, 2.0.7, 2.1.7; Bouncycastle Bcmail-Fips 1.0.7, 2.0.7, 2.1.7. Check the vendor advisory for mitigations.

References

• https://github.com/bcgit/bc-java/commit/2f81b22d559b3a1b026388e1ca78dd547384def8
• https://github.com/bcgit/bc-java/commit/fd89fe918b37fea1c71e95fae50284a325b09721
• https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9059641

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