{"id":"CVE-2026-71892","summary":"CMS key-transport recipient key-size validation never runs for RFC 9709 HKDF-derived keys","details":"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).","modified":"2026-10-22T16:39:14.343879758Z","published":"2026-10-03T08:30:26.982Z","related":["SUSE-SU-2026:4797-1","openSUSE-SU-2026:12090-1"],"database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/71xxx/CVE-2026-71892.json","unresolved_ranges":[{"extracted_events":[{"range":[{"introduced":"2.0.7"},{"fixed":"2.0.13"},{"introduced":"2.1.0"},{"fixed":"2.1.13"}],"source":"AFFECTED_FIELD","strategy":"StandardRange"}]}],"cna_assigner":"bcorg","cwe_ids":["CWE-697"]},"references":[{"type":"WEB","url":"https://www.bouncycastle.org/download/bouncy-castle-java-fips/"},{"type":"WEB","url":"https://www.bouncycastle.org/download/bouncy-castle-java/"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/71xxx/CVE-2026-71892.json"},{"type":"ADVISORY","url":"https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9071892"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-71892"},{"type":"FIX","url":"https://github.com/bcgit/bc-java/commit/be0a7d925c818ef2f338bcec55178b9b6336dfc3"},{"type":"PACKAGE","url":"https://github.com/bcgit/bc-java"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/bcgit/bc-java","events":[{"introduced":"30c6cc60ef5aa9062a083a8cea3e5c4f96d91a2a"},{"fixed":"eacda831fbe15b272933e40841d8b0827b556fae"},{"fixed":"be0a7d925c818ef2f338bcec55178b9b6336dfc3"}],"database_specific":{"extracted_events":[{"strategy":"StandardRange","range":[{"introduced":"1.78"},{"fixed":"1.86"}],"source":"AFFECTED_FIELD"},{"source":"REFERENCES_COMMIT","range":[{"fixed":"be0a7d925c818ef2f338bcec55178b9b6336dfc3"}]}]}}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-71892.json","vanir_signatures":[{"signature_version":"v1","source":"https://github.com/bcgit/bc-java/commit/be0a7d925c818ef2f338bcec55178b9b6336dfc3","target":{"file":"pkix/src/test/java/org/bouncycastle/cms/test/NewEnvelopedDataTest.java"},"deprecated":false,"digest":{"line_hashes":["233053073865261256262707398897418640123","239266541323147591071643525384677377037","83919457564507238264954193023659474809"],"threshold":0.9},"id":"CVE-2026-71892-6ac7d28c","signature_type":"Line"},{"signature_version":"v1","source":"https://github.com/bcgit/bc-java/commit/be0a7d925c818ef2f338bcec55178b9b6336dfc3","target":{"file":"pkix/src/main/java/org/bouncycastle/cms/jcajce/JceKeyTransRecipient.java"},"deprecated":false,"digest":{"threshold":0.9,"line_hashes":["315010033409212118055574421304138842911","122908921083836284355962816996253024005","187012734992806815947249353482734482351","166204105133335646495802624534614245298"]},"id":"CVE-2026-71892-bb0d3748","signature_type":"Line"},{"id":"CVE-2026-71892-bea51009","signature_type":"Function","signature_version":"v1","source":"https://github.com/bcgit/bc-java/commit/be0a7d925c818ef2f338bcec55178b9b6336dfc3","target":{"file":"pkix/src/main/java/org/bouncycastle/cms/jcajce/JceKeyTransRecipient.java","function":"extractSecretKey"},"deprecated":false,"digest":{"function_hash":"56121212132460458868786810564832878139","length":2854}}],"vanir_signatures_modified":"2026-10-22T16:39:14Z"}}],"schema_version":"1.9.2","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/U:Amber"}]}