{"id":"CVE-2026-73309","aliases":["EUVD-2026-72780","GHSA-pr5w-fh2v-7c9q"],"status":"published","title":"XenForo \u003c 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.","severity":{"version":"4.0","score":9.1,"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","level":"critical","assessor":"cna","from":"cve"},"epss":{"day":"2026-11-09","score":0.00685,"percentile":0.52857,"model":"v2026.06.15"},"facts":{"in_kev":false,"known_exploited":false,"public_exploit":true,"fix_available":false},"cwes":["CWE-697"],"published":"2026-09-08T13:15:50Z","modified":"2026-10-01T15:20:31Z","exploits":[{"source":"pocgithub","id":"BomboBombone/CVE-2026-73309","title":"BomboBombone/CVE-2026-73309","date":"2026-09-08","url":"https://github.com/BomboBombone/CVE-2026-73309"}],"products":[{"vendor":"xenforo","product":"xenforo"}],"references":[{"url":"https://xenforo.com/community/threads/security-fixes-released-for-all-xenforo-and-media-gallery-versions-2-2-0-2-3-12.239856/","tags":["vendor-advisory","patch","Release Notes"]},{"url":"https://xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857/","tags":["release-notes","Release Notes"]},{"url":"https://bombobombone.github.io/posts/cve-2026-73309/","tags":["technical-description","Exploit","Third Party Advisory"]},{"url":"https://github.com/BomboBombone/CVE-2026-73309","tags":["exploit","Third Party Advisory"]},{"url":"https://www.vulncheck.com/advisories/xenforo-authentication-bypass-via-oauth2-token-endpoint","tags":["third-party-advisory","Third Party Advisory"]},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-73309"},{"url":"https://xenforo.com/community/threads/security-fixes-released-for-all-xenforo-and-media-gallery-versions-2-2-0-2-3-12.239856"},{"url":"https://xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857"},{"url":"https://bombobombone.github.io/posts/cve-2026-73309"},{"url":"https://github.com/advisories/GHSA-pr5w-fh2v-7c9q"}],"sources":{"cve":[{"id":"CVE-2026-73309","title":"XenForo \u003c 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.","status":"published","published":"2026-09-08T13:15:50.743Z","modified":"2026-10-01T15:20:31.394Z","cvss":[{"version":"4.0","score":9.1,"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","level":"critical","assessor":"cna"},{"version":"3.1","score":7.4,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N","level":"high","assessor":"cna"}],"cwes":["CWE-697"],"updated_at":"2026-11-02T13:43:22.599321Z"}],"euvd":[{"id":"EUVD-2026-72780","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.","status":"published","published":"2026-09-08T13:15:50Z","modified":"2026-10-01T15:20:31Z","cvss":[{"version":"4.0","score":9.1,"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","level":"critical"}],"updated_at":"2026-11-02T17:27:45.358437Z"}],"ghsa":[{"id":"GHSA-pr5w-fh2v-7c9q","title":"XenForo before 2.3.13 contains an authentication bypass vulnerability in the OAuth2 token...","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.","status":"published","published":"2026-09-08T15:31:54Z","modified":"2026-09-09T03:30:35Z","cvss":[{"version":"4.0","score":9.1,"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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","level":"critical"},{"version":"3.1","score":7.4,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N","level":"high"}],"cwes":["CWE-697"],"updated_at":"2026-11-02T15:11:36.851913Z"}],"nvd":[{"id":"CVE-2026-73309","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.","status":"published","published":"2026-09-08T14:17:24.913Z","modified":"2026-09-11T20:33:42.98Z","cvss":[{"version":"4.0","score":9.1,"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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X","level":"critical","assessor":"secondary"},{"version":"3.1","score":7.4,"vector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N","level":"high","assessor":"secondary"},{"version":"3.1","score":9.1,"vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N","level":"critical","assessor":"primary"}],"cwes":["CWE-697"],"updated_at":"2026-11-02T14:12:44.436435Z"}]}}