CVE-2026-59640: OpenPGP CFB quick-check oracle active on symmetric/session-key paths

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% 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-203

Description

In Bouncy Castle for Java before 1.85, OpenPGP CFB quick-check oracle active on symmetric/session-key paths. 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: 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

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