Key-Size Validation Flaw in Bouncy Castle for Java

CVE-2026-71892

What is CVE-2026-71892?

A flaw exists in Bouncy Castle for Java prior to version 1.86, where the opt-in key-size validation for CMS key-transport recipients did not execute as intended with messages employing RFC 9709 content-encryption key derivation. The validation incorrectly compared an encrypted-key byte array against the id algorithm identifier, leading to a bypass of the critical key-size verification process. Consequently, this allowed for a potential mismatch between the derived content-encryption key size and the expected size, thus compromising the integrity of encrypted data. Users with certain configurations or those not enabling validation remain unaffected, but the flaw poses a significant risk for specific scenarios.

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