{"id":"CVE-2026-73309","title":"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 parameter…","summary":"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 parameter…","severity":"high","cvss":7.4,"cvssVector":"CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N","cwe":["CWE-697"],"vendor":"xenforo","product":"xenforo","affected":["xenforo < 2.3.13"],"patched":["xenforo 2.3.13"],"published":"2026-09-08","updated":"2026-09-11","sourceUpdated":"2026-09-11T20:33:42.980","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-73309","references":[{"url":"https://bombobombone.github.io/posts/cve-2026-73309/","label":"disclosure@vulncheck.com"},{"url":"https://github.com/BomboBombone/CVE-2026-73309","label":"disclosure@vulncheck.com"},{"url":"https://www.vulncheck.com/advisories/xenforo-authentication-bypass-via-oauth2-token-endpoint","label":"disclosure@vulncheck.com"},{"url":"https://xenforo.com/community/threads/security-fixes-released-for-all-xenforo-and-media-gallery-versions-2-2-0-2-3-12.239856/","label":"disclosure@vulncheck.com"},{"url":"https://xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857/","label":"disclosure@vulncheck.com"}],"tags":["nvd","exploit-available","cve.org"],"epss":0.00476,"epssPercentile":0.40143,"exploits":{"github":1,"githubRepos":["https://github.com/BomboBombone/CVE-2026-73309"],"checkedAt":"2026-09-21T15:30:28.805Z"},"exploitAvailable":true,"ssvc":{"exploitation":"poc","automatable":"no","technicalImpact":"total","timestamp":"2026-09-09T16:01:33.140807Z"},"ingestedAt":"2026-09-08T15:33:26.984Z","slug":"CVE-2026-73309","body":"## Overview\n\nXenForo 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.\n\n## Affected\n\n- `xenforo < 2.3.13`\n\n## Remediation\n\nUpgrade past the affected range:\n\n- `xenforo 2.3.13`","depth":"midnight","depthScore":53,"depthScoreParts":{"impact":40.7,"likelihood":0.1,"exploitation":12,"ransomware":0},"changes":[{"seq":8348,"id":"CVE-2026-73309","ts":1788920417161,"field":"exploit_available","old":"false","new":"true"}]}