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Fencer Vulns
medium 6.9

CVE-2026-71892 json

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

published 2026-10-03 36 d ago modified 2026-10-06 33 d ago also EUVD-2026-91989

cvss
6.9
version 4.0, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 6%
public exploits
0
none known

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).

Patch / fix

  • Legion of the Bouncy Castle Inc. BC-JAVA 1.86
  • Legion of the Bouncy Castle Inc. BC-FJA 2.0.13, 2.1.13
  • bouncycastle Debian 14 1.86-1

debian advisories DEBIAN-CVE-2026-71892

  • bouncycastle SLES for SAP applications 16.0, SLES 16.0 1.86-160000.1.1
  • bouncycastle SLES for SAP 15 SP6, SLES for SAP 15 SP5, SLES for SAP 15 SP4 +8 more 1.86-150200.3.41.1

suse advisories SUSE-SU-2026:24461-1SUSE-SU-2026:4797-1

  • bouncycastle openSUSE Leap 16.0 1.86-160000.1.1
  • bouncycastle openSUSE Tumbleweed 1.86-1.1

opensuse advisories openSUSE-SU-2026:22169-1openSUSE-SU-2026:12090-1

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-71892 updated cvss 6.5

org.bouncycastle/bcpkix-jdk18on: org.bouncycastle/bcpkix-fips: bouncycastle: Bouncy Castle: Key-size validation bypass via improper algorithm check

  • Red Hat OpenShift Developer Tools and Services jenkins, jenkins-2-plugins, ocp-tools-4/jenkins-rhel8, ocp-tools-4/jenkins-rhel9 Red Hat AMQ Broker 7 bcpkix-jdk18on Red Hat Ansible Automation Platform 2 ansible-automation-platform-27/de-minimal-rhel9, ansible-automation-platform-27/de-supported-rhel9 Red Hat build of Apache Camel 4 for Quarkus 3 bcpkix-jdk18on Red Hat build of Apache Camel for Spring Boot 4 bcpkix-jdk18on Red Hat Build of Keycloak bcpkix-jdk18on, rhbk/keycloak-rhel9
    +9 more products
    Red Hat build of Quarkus bcpkix-jdk18on Red Hat Ceph Storage 9 liborc, liborc2, libarrow, parquet-libs Red Hat JBoss Enterprise Application Platform 7 bcpkix-jdk18on, jboss-eap-7/eap74-els-openjdk8-openshift-rhel8, jboss-eap-7/eap74-els-openjdk11-openshift-rhel8, jboss-eap-7/eap74-els-openjdk17-openshift-rhel8 Red Hat JBoss Enterprise Application Platform 8 bcpkix-jdk18on Red Hat JBoss Enterprise Application Platform Expansion Pack bcpkix-jdk18on Red Hat OpenShift AI (RHOAI) rhoai/odh-modelmesh-rhel9 Red Hat OpenShift Dev Spaces devspaces/openvsx-rhel9, devspaces/jetbrains-ide-rhel9, devspaces/pluginregistry-rhel9 Red Hat Satellite 6 candlepin, candlepin-selinux Red Hat Single Sign-On 7 bcpkix-jdk18on
    affected: workaround, no fix available “Validate decrypted content-encryption key lengths directly within application logic after recipient processing, or reject CMS envelopes utilizing RFC 9709 HKDF key derivation.”
  • Red Hat Enterprise Linux 8 resteasy, resteasy-javadoc Red Hat Enterprise Linux 9 resteasy, pki-resteasy-core, pki-resteasy-client, pki-resteasy-jackson2-provider, pki-resteasy-servlet-initializer Red Hat Fuse 7 bcpkix-jdk15on, bcpkix-jdk18on, bcpkix-jdk15to18 Red Hat JBoss Enterprise Application Platform 7 bcpkix-jdk15on
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
34 d ago

Exploit prediction

0.17% chance of exploitation in the next 30 days, higher than 6% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 4.0 6.9 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
CNA 4.0 6.9 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:Amber

Affected products

  • Legion of the Bouncy Castle Inc. BC-JAVA
  • Legion of the Bouncy Castle Inc. BC-FJA

Classification

Weakness

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.