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AIKIDO-2026-450423

bcpg-jdk18on is vulnerable to Observable Discrepancy

Observable DiscrepancyCVE-2026-59640 Published Aug 5, 2026

87

High Risk

This Affects:

JAVAbcpg-jdk18on
0.0.1 - 1.84.0
Fixed in 1.85.0
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TL;DR

Bouncy Castle's OpenPGP decryption keeps the legacy CFB quick-check bytes active on the symmetric-key and session-key paths. Because a quick-check mismatch is observable, the routine behaves as a decryption oracle that leaks information about the underlying key or plaintext. Repeated queries let confidential key material and message content be recovered. The fix removes the exploitable quick-check oracle on those paths.

Who does this affect?

You are affected if you are using a version that falls within the vulnerable range and your application decrypts OpenPGP messages that use the symmetric-key or session-key CFB (non-AEAD) path with externally supplied input.

Background info

bcpg-jdk18on is vulnerable to Observable Discrepancy in versions 0.0.1 - 1.84.0.

How to fix this

Upgrade the org.bouncycastle:bcpg-jdk18on library to the patch version.

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