{"id":"CVE-2026-71892","revision":"ea3e6b008a4e414b8e252263fb8b7f5a","records":[{"revision":"ea3e6b008a4e414b8e252263fb8b7f5a","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-71892","aliases":[],"title":"CMS key-transport recipient key-size validation never runs for RFC 9709 HKDF-derived keys","description":"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).","state":0,"publishedAt":"2026-10-03T08:30:26.982+00:00","modifiedAt":"2026-10-05T16:58:40.411+00:00","affected":[{"ecosystem":"https://www.bouncycastle.org/download/bouncy-castle-java/","name":"bcpkix","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"vendor\": \"Legion of the Bouncy Castle Inc.\",\n                    \"product\": \"BC-JAVA\",\n                    \"platforms\": [\n                        \"all\"\n                    ],\n                    \"collectionURL\": \"https://www.bouncycastle.org/download/bouncy-castle-java/\",\n                    \"packageName\": \"bcpkix\",\n                    \"repo\": \"https://github.com/bcgit/bc-java\",\n                    \"packageURL\": \"pkg:maven/org.bouncycastle/bcpkix-jdk18on\",\n                    \"modules\": [\n                        \"pkix\"\n                    ],\n                    \"programFiles\": [\n                        \"JceKeyTransRecipient\"\n                    ],\n                    \"versions\": [\n                        {\n                            \"status\": \"affected\",\n                            \"version\": \"1.78\",\n                            \"lessThan\": \"1.86\",\n                            \"versionType\": \"maven\"\n                        }\n                    ],\n                    \"defaultStatus\": \"unaffected\"\n                }"},{"ecosystem":"https://www.bouncycastle.org/download/bouncy-castle-java-fips/","name":"bcpkix-fips","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"vendor\": \"Legion of the Bouncy Castle Inc.\",\n                    \"product\": \"BC-FJA\",\n                    \"platforms\": [\n                        \"all\"\n                    ],\n                    \"collectionURL\": \"https://www.bouncycastle.org/download/bouncy-castle-java-fips/\",\n                    \"packageName\": \"bcpkix-fips\",\n                    \"packageURL\": \"pkg:maven/org.bouncycastle/bcpkix-fips\",\n                    \"versions\": [\n                        {\n                            \"status\": \"affected\",\n                            \"version\": \"2.0.7\",\n                            \"lessThan\": \"2.0.13\",\n                            \"versionType\": \"maven\"\n                        },\n                        {\n                            \"status\": \"affected\",\n                            \"version\": \"2.1.0\",\n                            \"lessThan\": \"2.1.13\",\n                            \"versionType\": \"maven\"\n                        }\n                    ],\n                    \"defaultStatus\": \"unaffected\"\n                }"}],"metrics":[{"system":"CVSS 4.0","vector":"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","score":6.9,"severity":"MEDIUM"}],"references":["https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9071892","https://github.com/bcgit/bc-java/commit/be0a7d925c818ef2f338bcec55178b9b6336dfc3"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-71892","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-71892","identifiers":["CVE-2026-71892"]},"retained":false,"historicalAffected":[]}],"coverage":[]}