{"id":"UBUNTU-CVE-2026-71892","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).","modified":"2026-10-05T13:04:12.526023747Z","published":"2026-10-05T00:00:00Z","upstream":["CVE-2026-71892"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2026-71892"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2026-71892"},{"type":"REPORT","url":"https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9071892"},{"type":"REPORT","url":"https://github.com/bcgit/bc-java/commit/be0a7d925c818ef2f338bcec55178b9b6336dfc3"}],"affected":[{"package":{"name":"bouncycastle","ecosystem":"Ubuntu:Pro:16.04:LTS","purl":"pkg:deb/ubuntu/bouncycastle?arch=source&distro=esm-apps%2Fxenial"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.49+dfsg-3ubuntu1","1.51-4ubuntu1","1.51-4ubuntu1+esm1"],"ecosystem_specific":{"binaries":[{"binary_version":"1.51-4ubuntu1+esm1","binary_name":"libbcmail-java"},{"binary_name":"libbcpg-java","binary_version":"1.51-4ubuntu1+esm1"},{"binary_name":"libbcpkix-java","binary_version":"1.51-4ubuntu1+esm1"},{"binary_name":"libbcprov-java","binary_version":"1.51-4ubuntu1+esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-71892.json"}},{"package":{"name":"bouncycastle","ecosystem":"Ubuntu:Pro:18.04:LTS","purl":"pkg:deb/ubuntu/bouncycastle?arch=source&distro=esm-apps%2Fbionic"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.57-1","1.58-1","1.59-1","1.59-1ubuntu0.1~esm1"],"ecosystem_specific":{"binaries":[{"binary_name":"libbcmail-java","binary_version":"1.59-1ubuntu0.1~esm1"},{"binary_name":"libbcpg-java","binary_version":"1.59-1ubuntu0.1~esm1"},{"binary_version":"1.59-1ubuntu0.1~esm1","binary_name":"libbcpkix-java"},{"binary_name":"libbcprov-java","binary_version":"1.59-1ubuntu0.1~esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-71892.json"}},{"package":{"name":"bouncycastle","ecosystem":"Ubuntu:Pro:20.04:LTS","purl":"pkg:deb/ubuntu/bouncycastle?arch=source&distro=esm-apps%2Ffocal"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.61-1","1.61-1ubuntu0.1~esm1"],"ecosystem_specific":{"binaries":[{"binary_version":"1.61-1ubuntu0.1~esm1","binary_name":"libbcmail-java"},{"binary_name":"libbcpg-java","binary_version":"1.61-1ubuntu0.1~esm1"},{"binary_name":"libbcpkix-java","binary_version":"1.61-1ubuntu0.1~esm1"},{"binary_name":"libbcprov-java","binary_version":"1.61-1ubuntu0.1~esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-71892.json"}},{"package":{"name":"bouncycastle","ecosystem":"Ubuntu:Pro:22.04:LTS","purl":"pkg:deb/ubuntu/bouncycastle?arch=source&distro=esm-apps%2Fjammy"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.68-2","1.68-4","1.68-5","1.68-5ubuntu0.1~esm1"],"ecosystem_specific":{"binaries":[{"binary_name":"libbcmail-java","binary_version":"1.68-5ubuntu0.1~esm1"},{"binary_name":"libbcpg-java","binary_version":"1.68-5ubuntu0.1~esm1"},{"binary_version":"1.68-5ubuntu0.1~esm1","binary_name":"libbcpkix-java"},{"binary_name":"libbcprov-java","binary_version":"1.68-5ubuntu0.1~esm1"},{"binary_name":"libbctls-java","binary_version":"1.68-5ubuntu0.1~esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-71892.json"}},{"package":{"name":"bouncycastle","ecosystem":"Ubuntu:Pro:24.04:LTS","purl":"pkg:deb/ubuntu/bouncycastle?arch=source&distro=esm-apps%2Fnoble"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.72-2","1.77-1","1.77-1ubuntu0.1~esm1"],"ecosystem_specific":{"binaries":[{"binary_name":"libbcjmail-java","binary_version":"1.77-1ubuntu0.1~esm1"},{"binary_name":"libbcmail-java","binary_version":"1.77-1ubuntu0.1~esm1"},{"binary_name":"libbcpg-java","binary_version":"1.77-1ubuntu0.1~esm1"},{"binary_name":"libbcpkix-java","binary_version":"1.77-1ubuntu0.1~esm1"},{"binary_version":"1.77-1ubuntu0.1~esm1","binary_name":"libbcprov-java"},{"binary_name":"libbctls-java","binary_version":"1.77-1ubuntu0.1~esm1"},{"binary_name":"libbcutil-java","binary_version":"1.77-1ubuntu0.1~esm1"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-71892.json"}},{"package":{"name":"bouncycastle","ecosystem":"Ubuntu:26.04:LTS","purl":"pkg:deb/ubuntu/bouncycastle?arch=source&distro=resolute"},"ranges":[{"type":"ECOSYSTEM","events":[{"introduced":"0"}]}],"versions":["1.80-3"],"ecosystem_specific":{"binaries":[{"binary_name":"libbcjmail-java","binary_version":"1.80-3"},{"binary_version":"1.80-3","binary_name":"libbcmail-java"},{"binary_version":"1.80-3","binary_name":"libbcpg-java"},{"binary_name":"libbcpkix-java","binary_version":"1.80-3"},{"binary_name":"libbcprov-java","binary_version":"1.80-3"},{"binary_name":"libbctls-java","binary_versio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