CVE-2026-71892

Name of the Vulnerable Software and Affected Versions Bouncy Castle for Java versions prior to 1.86 Bouncy Castle for Java FIPS (BC-FJA) versions prior to bcpkix-fips 2.0.13 Bouncy Castle for Java FIPS (BC-FJA) versions prior to bcpkix-fips 2.1.13

Description Opt-in key-size validation for CMS key-transport recipients fails to execute for messages using RFC 9709 content-encryption key derivation (id-alg-cek-hkdf-sha256). This occurs because the system incorrectly compares an encrypted-key byte array against an ASN1ObjectIdentifier, resulting in a failed check that bypasses the key-size lookup. Consequently, EnvelopedData or AuthEnvelopedData with an HKDF-derived content-encryption key that does not match the advertised algorithm's key size is accepted, even when validation is enabled via the setKeySizeValidation(true) method in the org.bouncycastle.cms.jcajce.JceKeyTransRecipient class. This effectively disables the API mechanism for enforcing recovered key size for these specific messages.

Recommendations Update Bouncy Castle for Java to version 1.86 or later. Update Bouncy Castle for Java FIPS (BC-FJA) to bcpkix-fips version 2.0.13 or later. Update Bouncy Castle for Java FIPS (BC-FJA) to bcpkix-fips version 2.1.13 or later.