Skip to content
Heist/ feed
Medium

CMS key-transport recipient key-size validation never runs for RFC 9709 HKDF-derived keys

Type: advisorySource: Official CVE List1 source record

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

Announced Source revision 1
Original source ↗

CVE-2026-71892

Primary source · Revision 1

Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.

Security context

Source reference: cve:CVE-2026-71892

BC-JAVA

Source reference: /containers/cna/affected/0/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

BC-FJA

Source reference: /containers/cna/affected/1/product

Affected versions
Not stated in this record
Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

Structured affected-version data

Original package identities and version rules from this source.

[
  {
    "repo": "https://github.com/bcgit/bc-java",
    "vendor": "Legion of the Bouncy Castle Inc.",
    "modules": [
      "pkix"
    ],
    "product": "BC-JAVA",
    "versions": [
      {
        "status": "affected",
        "version": "1.78",
        "lessThan": "1.86",
        "versionType": "maven"
      }
    ],
    "platforms": [
      "all"
    ],
    "packageURL": "pkg:maven/org.bouncycastle/bcpkix-jdk18on",
    "packageName": "bcpkix",
    "programFiles": [
      "JceKeyTransRecipient"
    ],
    "collectionURL": "https://www.bouncycastle.org/download/bouncy-castle-java/",
    "defaultStatus": "unaffected"
  },
  {
    "vendor": "Legion of the Bouncy Castle Inc.",
    "product": "BC-FJA",
    "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"
      }
    ],
    "platforms": [
      "all"
    ],
    "packageURL": "pkg:maven/org.bouncycastle/bcpkix-fips",
    "packageName": "bcpkix-fips",
    "collectionURL": "https://www.bouncycastle.org/download/bouncy-castle-java-fips/",
    "defaultStatus": "unaffected"
  }
]
Related CVEs
CVE-2026-71892

Source reference: /cveMetadata/cveId

Publisher severity

medium

Source reference: /containers/cna/metrics

Event
#8803 · Revision 1
Added to Heist Feed
Publisher date
Read the original announcement