CMS key-transport recipient key-size validation never runs for RFC 9709 HKDF-derived keys
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Attack requirements
- None
- Impact type
- —
- Confidentiality · integrity · availability
- Low · Low · None
- Fix status
- Partial Red Hat: 15 without a fix
Attack profile from CVSS 4.0 · CNA. Fix status from CNA and Red Hat.
Summary
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).
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- Yes
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| Legion of the Bouncy Castle Inc. | BC-JAVA | 1.78 to before 1.86 | 1.86 | Patch available | CNA |
| Legion of the Bouncy Castle Inc. | BC-FJA | 2.0.7 to before 2.0.13; 2.1.0 to before 2.1.13 | 2.0.13, 2.1.13 | Patch available | CNA |
- BC-JAVA VendorLegion of the Bouncy Castle Inc. Affected 1.78 to before 1.86 Fixed in 1.86 Patch available CNA
- BC-FJA VendorLegion of the Bouncy Castle Inc. Affected 2.0.7 to before 2.0.13; 2.1.0 to before 2.1.13 Fixed in 2.0.13, 2.1.13 Patch available CNA
CPE names Threatist (inferred) · 1
Inferred from how NVD named this product before; not given by a source.
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:bouncycastle:bc-java:*:*:*:*:*:*:*:* | — | — | Legion of the Bouncy Castle Inc. |
- cpe:2.3:a:bouncycastle:bc-java:*:*:*:*:*:*:*:* Versions — — ·Legion of the Bouncy Castle Inc.
Remediation
- Fix · CNA BC-JAVA (Legion of the Bouncy Castle Inc.) Fixed in 1.86
- Fix · CNA BC-FJA (Legion of the Bouncy Castle Inc.) Fixed in 2.0.13, 2.1.13
Fixed in the same release
Records fixed by the same vendor advisory or release, as the CNA lists them.
- Release ·
Legion of the Bouncy Castle BC-JAVA 1.86
11 records Highest priority Priority MEDIUM 4 MEDIUM, 7 LOW
Other records, highest priority first
- TI-2026-67477 MLS external commit can remove an arbitrary group memberPriority MEDIUM 43
- TI-2026-67476 PKIXCertPathReviewer does not apply X.509 name constraints to the target certificatePriority MEDIUM 43
- TI-2026-67475 CMS AuthenticatedData exposes attacker-inserted authAttrs when digestAlgorithm is absentPriority MEDIUM 42
Vendor assessments
Red Hat
Red Hat rating: Moderate. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| OpenShift Developer Tools and Services | Affected | No fix yet: Fix deferred |
| Red Hat AMQ Broker 7 | Affected | No fix yet: Fix deferred |
| Red Hat Ansible Automation Platform 2 | Affected | No fix yet: Fix deferred |
| Red Hat Build of Keycloak | Affected | No fix yet: Fix deferred |
| Red Hat Ceph Storage 9 | Affected | No fix yet: Fix deferred |
| Red Hat JBoss Enterprise Application Platform 7 | Affected | No fix yet: Fix deferred |
| Red Hat JBoss Enterprise Application Platform 8 | Affected | No fix yet: Fix deferred |
| Red Hat JBoss Enterprise Application Platform Expansion Pack | Affected | No fix yet: Fix deferred |
| Red Hat OpenShift AI (RHOAI) | Affected | No fix yet: Fix deferred |
| Red Hat OpenShift Dev Spaces | Affected | No fix yet: Fix deferred |
| Red Hat Satellite 6 | Affected | No fix yet: Fix deferred |
| Red Hat Single Sign-On 7 | Affected | No fix yet: Fix deferred |
| Red Hat build of Apache Camel 4 for Quarkus 3 | Affected | No fix yet: Fix deferred |
| Red Hat build of Apache Camel for Spring Boot 4 | Affected | No fix yet: Fix deferred |
| Red Hat build of Quarkus | Affected | No fix yet: Fix deferred |
Not affected: 4 products
- Red Hat Enterprise Linux 8
- Red Hat Enterprise Linux 9
- Red Hat Fuse 7
- Red Hat JBoss Enterprise Application Platform 7
Timeline
- 2026-10-03 Threatist record created from CVE-2026-71892
- 2026-10-03 Alias added: GHSA-x42w-4gqh-qrvm
- 2026-10-04 Priority changed: MEDIUM → LOW
- 2026-10-05 CISA SSVC decision points changed
- 2026-10-15 Affected versions changed · Red Hat
- 2026-10-15 CVSS score added · Red Hat
References
More Legion of the Bouncy Castle Inc. vulnerabilities
- TI-2018-15967 Legion of the Bouncy Castle Legion of the Bouncy Castle Java Cryptography APIs 1.58 up to… CVSS 3.1CRITICAL 9.8
- TI-2017-09736 BouncyCastle JCE TLS Bleichenbacher/ROBOT CVSS 3.0HIGH 7.5
- TI-2026-42545 MTI/A0 DH agreement exponentiates unvalidated peer value CVSS 4.0CRITICAL 9.3
- TI-2026-42533 JSSE hostname verifier CN-fallback enabled by default despite documented opt-in CVSS 4.0CRITICAL 9.3
- TI-2026-41816 Stapled OCSP response accepted without binding to the checked certificate CVSS 4.0CRITICAL 9.3
- TI-2026-07701 Name Constraints bypass via trailing dot in rfc822Name and URI CVSS 4.0CRITICAL 9.3
Sources
- CVE-2026-71892 · CVE Program
- CVE-2026-71892 · NVD
- FIRST EPSS
- GHSA-x42w-4gqh-qrvm · GitHub Advisory Database · CC BY 4.0
- CVE-2026-71892 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences