{"id":"UBUNTU-CVE-2026-71886","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":"2026-10-05T13:04:12.564489640Z","published":"2026-10-05T00:00:00Z","upstream":["CVE-2026-71886"],"references":[{"type":"REPORT","url":"https://ubuntu.com/security/CVE-2026-71886"},{"type":"REPORT","url":"https://www.cve.org/CVERecord?id=CVE-2026-71886"},{"type":"REPORT","url":"https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9071886"},{"type":"REPORT","url":"https://github.com/bcgit/bc-java/commit/f0d5c8535aeff3f34b7b6b6289ee78c2ea36a3fb"}],"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_name":"libbcmail-java","binary_version":"1.51-4ubuntu1+esm1"},{"binary_name":"libbcpg-java","binary_version":"1.51-4ubuntu1+esm1"},{"binary_version":"1.51-4ubuntu1+esm1","binary_name":"libbcpkix-java"},{"binary_version":"1.51-4ubuntu1+esm1","binary_name":"libbcprov-java"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-71886.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_version":"1.59-1ubuntu0.1~esm1","binary_name":"libbcmail-java"},{"binary_name":"libbcpg-java","binary_version":"1.59-1ubuntu0.1~esm1"},{"binary_version":"1.59-1ubuntu0.1~esm1","binary_name":"libbcpkix-java"},{"binary_version":"1.59-1ubuntu0.1~esm1","binary_name":"libbcprov-java"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-71886.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_name":"libbcmail-java","binary_version":"1.61-1ubuntu0.1~esm1"},{"binary_name":"libbcpg-java","binary_version":"1.61-1ubuntu0.1~esm1"},{"binary_version":"1.61-1ubuntu0.1~esm1","binary_name":"libbcpkix-java"},{"binary_version":"1.61-1ubuntu0.1~esm1","binary_name":"libbcprov-java"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-71886.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_name":"libbcpkix-java","binary_version":"1.68-5ubuntu0.1~esm1"},{"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-2026-71886.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_version":"1.77-1ubuntu0.1~esm1","binary_name":"libbcjmail-java"},{"binary_name":"libbcmail-java","binary_version":"1.77-1ubuntu0.1~esm1"},{"binary_version":"1.77-1ubuntu0.1~esm1","binary_name":"libbcpg-java"},{"binary_name":"libbcpkix-java","binary_version":"1.77-1ubuntu0.1~esm1"},{"binary_version":"1.77-1ubuntu0.1~esm1","binary_name":"libbcprov-java"},{"binary_version":"1.77-1ubuntu0.1~esm1","binary_name":"libbctls-java"},{"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-2026-71886.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_version":"1.80-3","binary_name":"libbcjmail-java"},{"binary_version":"1.80-3","binary_name":"libbcmail-java"},{"binary_name":"libbcpg-java","binary_version":"1.80-3"},{"binary_version":"1.80-3","binary_name":"libbcpkix-java"},{"binary_version":"1.80-3","binary_name":"libbcprov-java"},{"binary_name":"libbctls-java","binary_version":"1.80-3"},{"binary_name":"libbcutil-java","binary_version":"1.80-3"}]},"database_specific":{"source":"https://github.com/canonical/ubuntu-security-notices/blob/main/osv/cve/2026/UBUNTU-CVE-2026-71886.json"}}],"schema_version":"1.9.0","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"},{"type":"Ubuntu","score":"medium"}]}