{"id":"CVE-2026-73309","revision":"c98a2415144f4b85af6db8d0da61a660","records":[{"revision":"c98a2415144f4b85af6db8d0da61a660","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-73309","aliases":[],"title":"XenForo < 2.3.13 Authentication Bypass via OAuth2 Token Endpoint","description":"XenForo before 2.3.13 contains an authentication bypass vulnerability in the OAuth2 token endpoint that allows unauthenticated attackers to obtain valid token pairs by submitting empty values for client_secret and code_verifier parameters. Attackers can exploit PHP truthy evaluation logic, which treats empty strings as false and skips client secret validation and PKCE code verifier validation, to exchange a valid authorization code for a token pair without proving client identity or holding the PKCE commitment.","state":0,"publishedAt":"2026-09-08T13:15:50.743+00:00","modifiedAt":"2026-10-01T15:20:31.394+00:00","affected":[{"ecosystem":"Vendor product","name":"XenForo","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"defaultStatus\": \"unaffected\",\n                    \"vendor\": \"XenForo\",\n                    \"product\": \"XenForo\",\n                    \"versions\": [\n                        {\n                            \"status\": \"affected\",\n                            \"version\": \"0\",\n                            \"versionType\": \"semver\",\n                            \"lessThan\": \"2.3.13\"\n                        }\n                    ]\n                }"}],"metrics":[{"system":"CVSS 4.0","vector":"CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N","score":9.1,"severity":"CRITICAL"},{"system":"CVSS 3.1","vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N","score":7.4,"severity":"HIGH"}],"references":["https://xenforo.com/community/threads/security-fixes-released-for-all-xenforo-and-media-gallery-versions-2-2-0-2-3-12.239856/","https://xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857/","https://bombobombone.github.io/posts/cve-2026-73309/","https://github.com/BomboBombone/CVE-2026-73309","https://www.vulncheck.com/advisories/xenforo-authentication-bypass-via-oauth2-token-endpoint"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-73309","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-73309","identifiers":["CVE-2026-73309"]},"retained":false,"historicalAffected":[]}],"coverage":[]}