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CVE-2026-12817: OpenPGP AEAD decryption skips final tag on chunk-aligned data

• Severity: high (CVSS 8.6 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 2026-08-31
• Weakness: CWE-354

Description

In Bouncy Castle for Java before 1.85, OpenPGP AEAD decryption skips final tag on chunk-aligned data. This issue also affects Bouncy Castle for Java LTS before 2.73.12, and Bouncy Castle for Java FIPS (BC-FJA) 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).

Affected products

• Legion of the Bouncy Castle Inc. BC-JAVA: before 1.85 — fixed in 1.85
• Bouncycastle Bcpg-Fips: from 1.0.7 before 1.0.13; from 2.0.8 before 2.0.13; from 2.1.10 before 2.1.13 — fixed in 1.0.13, 2.0.13, 2.1.13
• 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 Bcpg-Fips 1.0.13, 2.0.13, 2.1.13. Check the vendor advisory for mitigations.

References

• https://github.com/bcgit/bc-java/commit/4b712819846ec944379f4909101abac20f0ad4b0
• https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9012817

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