CVE-2026-73309 (GCVE-0-2026-73309)
Vulnerability from cvelistv5 – Published: 2026-09-08 13:15 – Updated: 2026-10-01 15:20
VLAI
EPSS
VEX
Title
XenForo < 2.3.13 Authentication Bypass via OAuth2 Token Endpoint
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 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
7.4 (High)
SSVC
Exploitation: poc
Automatable: no
Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-09-09 16:01 UTC
CWE
- CWE-697 - Incorrect Comparison
Assigner
References
5 references
| URL | Tags |
|---|---|
| https://xenforo.com/community/threads/security-fi… | vendor-advisorypatch |
| https://xenforo.com/community/threads/xenforo-2-3… | release-notes |
| https://bombobombone.github.io/posts/cve-2026-73309/ | technical-description |
| https://github.com/BomboBombone/CVE-2026-73309 | exploit |
| https://www.vulncheck.com/advisories/xenforo-auth… | third-party-advisory |
Impacted products
Date Public
2026-09-07 00:00
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