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.

Scores

EPSS (exploitation in 30 days)

0.17% · top 94% of all CVEs (6 Nov 2026)

CISA SSVC

Exploitation: none · Automatable: no · Technical impact: partial

The list uses the assigner's score when there is one, then CISA's, then NVD's: High 8.2.

Weakness

• CWE-863 Incorrect Authorization (opens in a new tab)All about CWE-863 and its CVEs
• CWE-285 Improper Authorization (opens in a new tab)All about CWE-285 and its CVEs

Affected products

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

  • affected 1.81 – < 1.86

References (2)

• https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9071886 (opens in a new tab)vendor-advisory
• https://github.com/bcgit/bc-java/commit/f0d5c8535aeff3f34b7b6b6289ee78c2ea36a3fb (opens in a new tab)patch

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisories (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2026-71886](https://trackcve.app/badge/CVE-2026-71886.svg)](https://trackcve.app/cve/CVE-2026-71886)

Record last updated 5 Oct 2026, 16:03 UTC.