CVE-2026-73309
critical · 9.1XenForo 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.
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
Weaknesses
Affected products
| Vendor | Product | Affected versions |
|---|---|---|
| xenforo | xenforo | < 2.3.13 |
Check a specific version with /api/v1/cve/match.
References
- 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
- 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/
Query this programmatically:
curl https://evil-db.io/api/v1/cve/CVE-2026-73309