{ "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": "

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).

" } ] } ], "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" } } ] } }