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