{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-71892","assignerOrgId":"91579145-5d7b-4cc5-b925-a0262ff19630","state":"PUBLISHED","assignerShortName":"bcorg","dateReserved":"2026-08-08T00:06:07.401Z","datePublished":"2026-10-03T08:30:26.982Z","dateUpdated":"2026-10-05T16:58:40.411Z"},"containers":{"cna":{"providerMetadata":{"orgId":"91579145-5d7b-4cc5-b925-a0262ff19630","shortName":"bcorg","dateUpdated":"2026-10-03T08:30:26.982Z"},"title":"CMS key-transport recipient key-size validation never runs for RFC 9709 HKDF-derived keys","problemTypes":[{"descriptions":[{"lang":"en","cweId":"CWE-697","description":"CWE-697 Incorrect Comparison","type":"CWE"}]}],"affected":[{"vendor":"Legion of the Bouncy Castle Inc.","product":"BC-JAVA","platforms":["all"],"collectionURL":"https://www.bouncycastle.org/download/bouncy-castle-java/","packageName":"bcpkix","repo":"https://github.com/bcgit/bc-java","packageURL":"pkg:maven/org.bouncycastle/bcpkix-jdk18on","modules":["pkix"],"programFiles":["JceKeyTransRecipient"],"versions":[{"status":"affected","version":"1.78","lessThan":"1.86","versionType":"maven"}],"defaultStatus":"unaffected"},{"vendor":"Legion of the Bouncy Castle Inc.","product":"BC-FJA","platforms":["all"],"collectionURL":"https://www.bouncycastle.org/download/bouncy-castle-java-fips/","packageName":"bcpkix-fips","packageURL":"pkg:maven/org.bouncycastle/bcpkix-fips","versions":[{"status":"affected","version":"2.0.7","lessThan":"2.0.13","versionType":"maven"},{"status":"affected","version":"2.1.0","lessThan":"2.1.13","versionType":"maven"}],"defaultStatus":"unaffected"}],"descriptions":[{"lang":"en","value":"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).","supportingMedia":[{"type":"text/html","base64":false,"value":"<p>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).</p>"}]}],"references":[{"url":"https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9071892","tags":["vendor-advisory"]},{"url":"https://github.com/bcgit/bc-java/commit/be0a7d925c818ef2f338bcec55178b9b6336dfc3","tags":["patch"]}],"metrics":[{"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}],"cvssV4_0":{"attackVector":"NETWORK","attackComplexity":"LOW","attackRequirements":"NONE","privilegesRequired":"NONE","userInteraction":"NONE","vulnConfidentialityImpact":"LOW","subConfidentialityImpact":"NONE","vulnIntegrityImpact":"LOW","subIntegrityImpact":"NONE","vulnAvailabilityImpact":"NONE","subAvailabilityImpact":"NONE","exploitMaturity":"NOT_DEFINED","Safety":"NOT_DEFINED","Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","valueDensity":"NOT_DEFINED","vulnerabilityResponseEffort":"NOT_DEFINED","providerUrgency":"AMBER","version":"4.0","baseSeverity":"MEDIUM","baseScore":6.9,"vectorString":"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"}}],"credits":[{"lang":"en","value":"Yu Bao from the PayPal Cyber Security Team","type":"reporter"}],"source":{"discovery":"EXTERNAL"},"x_generator":{"engine":"bc release-notes template"}},"adp":[{"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-10-05T16:58:15.636238Z","id":"CVE-2026-71892","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"title":"CISA ADP Vulnrichment","providerMetadata":{"orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","shortName":"CISA-ADP","dateUpdated":"2026-10-05T16:58:40.411Z"}}]}}