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CVE-2026-71892: Product identification pending

Severity

6.9 (MEDIUM)

Vendor

BOUNCY CASTLE FOR JAVA

Affected versions

Before 1.86

Fixed version

1.86

Patch status

Patched

Published

2026-10-03T09:17:05.913

Modified

2026-10-03T09:17:05.913

Why it matters

Vulnerability requiring standard triage and vendor validation.

Recommended admin actions

• Review during normal vulnerability triage unless the affected system is internet-facing or business-critical.
• Compare installed versions against the affected version range in the advisory.

Technical summary

In Bouncy Castle for Java before 1.86, the opt-in key-size validation on CMS key-transport recipients, org.bouncycastle.cms.jcajce.JceKeyTransRecipient.setKeySizeValidation(true), never ran for a message using RFC 9709 content-encryption key derivation (id-alg-cek-hkdf-sha256). The branch that should have selected the actual content-encryption algorithm carried in the key derivation AlgorithmIdentifier's parameters compared the encrypted-key byte array against the id-alg-cek-hkdf-sha256 object identifier, a comparison between a byte array and an ASN1ObjectIdentifier that is false for every possible input, so the check fell through to a key-size lookup on the outer wrapper OID. That OID identifies a key-derivation construction rather than a cipher and has no registered key size, so the size comparison was skipped entirely. A key-transport EnvelopedData or AuthEnvelopedData whose transported, HKDF-derived content-encryption key did not match the key size of the advertised content-encryption algorithm was therefore accepted even with validation explicitly enabled, silently defeating the only mechanism the API offers for enforcing recovered key size. The recipient now dispatches on the content-encryption AlgorithmIdentifier's algorithm OID, so validation checks the recovered key against the inner content-encryption algorithm. Messages with a matching key size, non-HKDF messages, and recipients that do not enable validation are unaffected. This issue also affects Bouncy Castle for Java FIPS (BC-FJA) before bcpkix-fips 2.0.13 (2.0.X series) and 2.1.13 (2.1.X series).

View the official NVD record for CVE-2026-71892

CVE data is sourced from NVD/CNA records and optional enrichment. Validate against the vendor advisory before taking production action.