{
  "affected": [
    {
      "ranges": [
        {
          "database_specific": {
            "extracted_events": [
              {
                "introduced": "1.78"
              },
              {
                "fixed": "1.86"
              }
            ],
            "source": "AFFECTED_FIELD"
          },
          "events": [
            {
              "introduced": "30c6cc60ef5aa9062a083a8cea3e5c4f96d91a2a"
            },
            {
              "fixed": "eacda831fbe15b272933e40841d8b0827b556fae"
            }
          ],
          "repo": "https://github.com/bcgit/bc-java",
          "type": "GIT"
        }
      ]
    }
  ],
  "database_specific": {
    "cna_assigner": "bcorg",
    "cwe_ids": [
      "CWE-697"
    ],
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/71xxx/CVE-2026-71892.json",
    "unresolved_ranges": [
      {
        "extracted_events": [
          {
            "introduced": "2.0.7"
          },
          {
            "fixed": "2.0.13"
          },
          {
            "introduced": "2.1.0"
          },
          {
            "fixed": "2.1.13"
          }
        ],
        "source": "AFFECTED_FIELD"
      }
    ]
  },
  "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).",
  "id": "CVE-2026-71892",
  "modified": "2026-10-06T02:30:40.453438364Z",
  "published": "2026-10-03T08:30:26.982Z",
  "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"
    }
  ],
  "schema_version": "1.9.0",
  "severity": [
    {
      "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",
      "type": "CVSS_V4"
    }
  ],
  "summary": "CMS key-transport recipient key-size validation never runs for RFC 9709 HKDF-derived keys"
}