{"id":"CVE-2026-71892","state":"PUBLISHED","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).","publishedAt":"2026-10-03T08:30:26.982Z","updatedAt":"2026-10-05T16:58:40.411Z","severity":{"score":6.9,"label":"Medium","version":"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","source":"bcorg"},"assigner":"bcorg","products":["Legion of the Bouncy Castle Inc. BC-JAVA","Legion of the Bouncy Castle Inc. BC-FJA"],"affected":[{"vendor":"Legion of the Bouncy Castle Inc.","product":"BC-JAVA","packageName":"bcpkix","packageURL":"pkg:maven/org.bouncycastle/bcpkix-jdk18on","defaultStatus":"unaffected","versions":[{"version":"1.78","status":"affected","lessThan":"1.86","versionType":"maven"}],"platforms":["all"],"collectionURL":"https://www.bouncycastle.org/download/bouncy-castle-java/","repo":"https://github.com/bcgit/bc-java","modules":["pkix"],"programFiles":["JceKeyTransRecipient"]},{"vendor":"Legion of the Bouncy Castle Inc.","product":"BC-FJA","packageName":"bcpkix-fips","packageURL":"pkg:maven/org.bouncycastle/bcpkix-fips","defaultStatus":"unaffected","versions":[{"version":"2.0.7","status":"affected","lessThan":"2.0.13","versionType":"maven"},{"version":"2.1.0","status":"affected","lessThan":"2.1.13","versionType":"maven"}],"platforms":["all"],"collectionURL":"https://www.bouncycastle.org/download/bouncy-castle-java-fips/"}],"references":["https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9071892","https://github.com/bcgit/bc-java/commit/be0a7d925c818ef2f338bcec55178b9b6336dfc3"],"weaknesses":["CWE-697"],"ingestedAt":"2026-10-29T20:12:49.727Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/71xxx/CVE-2026-71892.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-71892","state":"PUBLISHED","datePublished":"2026-10-03T08:30:26.982Z","dateUpdated":"2026-10-05T16:58:40.411Z","assignerShortName":"bcorg","assignerOrgId":"91579145-5d7b-4cc5-b925-a0262ff19630","dateReserved":"2026-08-08T00:06:07.401Z"},"containers":{"cna":{"title":"CMS key-transport recipient key-size validation never runs for RFC 9709 HKDF-derived keys","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)."}],"affected":[{"vendor":"Legion of the Bouncy Castle Inc.","product":"BC-JAVA","packageName":"bcpkix","packageURL":"pkg:maven/org.bouncycastle/bcpkix-jdk18on","defaultStatus":"unaffected","versions":[{"version":"1.78","status":"affected","lessThan":"1.86","versionType":"maven"}],"platforms":["all"],"collectionURL":"https://www.bouncycastle.org/download/bouncy-castle-java/","repo":"https://github.com/bcgit/bc-java","modules":["pkix"],"programFiles":["JceKeyTransRecipient"]},{"vendor":"Legion of the Bouncy Castle Inc.","product":"BC-FJA","packageName":"bcpkix-fips","packageURL":"pkg:maven/org.bouncycastle/bcpkix-fips","defaultStatus":"unaffected","versions":[{"version":"2.0.7","status":"affected","lessThan":"2.0.13","versionType":"maven"},{"version":"2.1.0","status":"affected","lessThan":"2.1.13","versionType":"maven"}],"platforms":["all"],"collectionURL":"https://www.bouncycastle.org/download/bouncy-castle-java-fips/"}],"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"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-697","lang":"en","description":"CWE-697 Incorrect Comparison","type":"CWE"}]}],"providerMetadata":{"shortName":"bcorg","orgId":"91579145-5d7b-4cc5-b925-a0262ff19630","dateUpdated":"2026-10-03T08:30:26.982Z"},"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":[{"title":"CISA ADP Vulnrichment","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"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-05T16:58:40.411Z"}}]}}}