{"id":"CVE-2026-71886","revision":"a84f197a5aa140b6911d8e22634b8b4e","records":[{"revision":"a84f197a5aa140b6911d8e22634b8b4e","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-71886","aliases":[],"title":"OpenPGP certification accepted from a subkey without certification authority","description":"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.","state":0,"publishedAt":"2026-10-03T08:46:33.868+00:00","modifiedAt":"2026-10-05T16:03:23.403+00:00","affected":[{"ecosystem":"https://www.bouncycastle.org/download/bouncy-castle-java/","name":"bcpg","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"vendor\": \"Legion of the Bouncy Castle Inc.\",\n                    \"product\": \"BC-JAVA\",\n                    \"platforms\": [\n                        \"all\"\n                    ],\n                    \"collectionURL\": \"https://www.bouncycastle.org/download/bouncy-castle-java/\",\n                    \"packageName\": \"bcpg\",\n                    \"repo\": \"https://github.com/bcgit/bc-java\",\n                    \"packageURL\": \"pkg:maven/org.bouncycastle/bcpg-jdk18on\",\n                    \"modules\": [\n                        \"pg\"\n                    ],\n                    \"programFiles\": [\n                        \"OpenPGPCertificate\"\n                    ],\n                    \"versions\": [\n                        {\n                            \"status\": \"affected\",\n                            \"version\": \"1.81\",\n                            \"lessThan\": \"1.86\",\n                            \"versionType\": \"maven\"\n                        }\n                    ],\n                    \"defaultStatus\": \"unaffected\"\n                }"}],"metrics":[{"system":"CVSS 4.0","vector":"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","score":8.2,"severity":"HIGH"}],"references":["https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9071886","https://github.com/bcgit/bc-java/commit/f0d5c8535aeff3f34b7b6b6289ee78c2ea36a3fb"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-71886","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-71886","identifiers":["CVE-2026-71886"]},"retained":false,"historicalAffected":[]}],"coverage":[]}