{"id":"CVE-2026-71886","summary":"OpenPGP certification accepted from a subkey without certification authority","details":"In Bouncy Castle for Java before 1.86, the high-level OpenPGP certificate API accepted a third-party certification or trust delegation from any component key of the issuing certificate, without requiring that component to have been granted the authority to certify. OpenPGPCertificate.getCertificationBy() and getDelegationBy() resolve a third-party signature by matching its issuer key identifier against every key of the third-party certificate, then verify the issuing component's binding chain and the signature itself; nothing checked that the issuing component carried the RFC 9580 sec. 5.2.3.29 certification key flag (CERTIFY_OTHER) when the signature was created. A subkey bound only with SIGN_DATA - the online signing subkey of exactly the offline-primary arrangement those key flags exist to express - could therefore issue a positive User ID certification over an attacker-controlled identity, or a full-trust depth-one direct-key delegation of introducer trust, and the API returned it as a valid signature chain attributed to the third-party certificate. An application treating getCertificationBy(...).isValid() or getDelegationBy(...) as an identity or trusted-introducer decision would attribute the attacker's assertion to the offline primary key. The same held for a legacy RSA subkey bound only for encryption, whose algorithm is nonetheless able to sign. This does not forge the primary key's signature or recover any private key; it promotes an already-compromised restricted subkey to the primary key's identity-issuing authority, defeating the containment the key-flag separation provides. A third-party certification or delegation is now attributed to the issuing certificate only when the component key that made it is the primary key, or is a subkey holding CERTIFY_OTHER when the signature was created, so certification-capable subkeys continue to be accepted; primary keys are accepted whatever their key flags say, since a primary key is certification-capable by construction and certificates carrying no key flags subpacket at all are common. Third-party revocations are deliberately outside the rule, since declining to honour one would keep trust alive rather than withdraw it.","modified":"2026-10-22T16:39:14.713311178Z","published":"2026-10-03T08:46:33.868Z","related":["SUSE-SU-2026:4797-1","openSUSE-SU-2026:12090-1"],"database_specific":{"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/71xxx/CVE-2026-71886.json","cna_assigner":"bcorg","cwe_ids":["CWE-285","CWE-863"]},"references":[{"type":"WEB","url":"https://www.bouncycastle.org/download/bouncy-castle-java/"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/71xxx/CVE-2026-71886.json"},{"type":"ADVISORY","url":"https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9071886"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-71886"},{"type":"FIX","url":"https://github.com/bcgit/bc-java/commit/f0d5c8535aeff3f34b7b6b6289ee78c2ea36a3fb"},{"type":"PACKAGE","url":"https://github.com/bcgit/bc-java"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/bcgit/bc-java","events":[{"introduced":"228211ecb973fe87fdd0fc4ab16ba0446ec1a29c"},{"fixed":"eacda831fbe15b272933e40841d8b0827b556fae"},{"fixed":"f0d5c8535aeff3f34b7b6b6289ee78c2ea36a3fb"}],"database_specific":{"extracted_events":[{"strategy":"StandardRange","range":[{"introduced":"1.81"},{"fixed":"1.86"}],"source":"AFFECTED_FIELD"},{"source":"REFERENCES_COMMIT","range":[{"fixed":"f0d5c8535aeff3f34b7b6b6289ee78c2ea36a3fb"}]}]}}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2026-71886.json","vanir_signatures":[{"deprecated":false,"digest":{"function_hash":"92728918085483818624135828885250796945","length":654},"id":"CVE-2026-71886-719a36c6","signature_type":"Function","signature_version":"v1","source":"https://github.com/bcgit/bc-java/commit/f0d5c8535aeff3f34b7b6b6289ee78c2ea36a3fb","target":{"file":"pg/src/main/java/org/bouncycastle/openpgp/api/OpenPGPCertificate.java","function":"getMergedDanglingExternalSignatureChainEndsFrom"}},{"deprecated":false,"digest":{"threshold":0.9,"line_hashes":["96044263478928036066923524062525021264","242487062344332550567517235893918196467","152891498374372822831571267334452984753","333006426170499316169006874622780740915"]},"id":"CVE-2026-71886-805740fb","signature_type":"Line","signature_version":"v1","source":"https://github.com/bcgit/bc-java/commit/f0d5c8535aeff3f34b7b6b6289ee78c2ea36a3fb","target":{"file":"pg/src/test/java/org/bouncycastle/openpgp/api/test/RegressionTest.java"}},{"target":{"file":"pg/src/main/java/org/bouncycastle/openpgp/api/OpenPGPCertificate.java"},"deprecated":false,"digest":{"line_hashes":["90602617907301426648126531739415962309","57142368514420324495394381481274598647","198483668386199754599530411782955208446","201586600117416069860992628273320755579","144638274316590469724206700312500581269","283782780981136109616440998703198800326","233536536377518901883844857438464715310","55105660343254344232119973270498110244"],"threshold":0.9},"id":"CVE-2026-71886-a840a4ea","signature_type":"Line","signature_version":"v1","source":"https://github.com/bcgit/bc-java/commit/f0d5c8535aeff3f34b7b6b6289ee78c2ea36a3fb"}],"vanir_signatures_modified":"2026-10-22T16:39:14Z"}}],"schema_version":"1.9.2","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/U:Amber"}]}