CVE-2026-73309 json
XenForo < 2.3.13 Authentication Bypass via OAuth2 Token Endpoint
published 2mo ago modified last mo. also EUVD-2026-72780
- cvss
- 7.4
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.7%
- EPSS 0.7% chance of exploitation in 30 days, percentile 53%
- public exploits
- 0
- none known
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.
Patch / fix
- XenForo XenForo 2.3.13
Is CVE-2026-73309 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.
Check with FencerCISA SSVC
- Exploitation
- Proof of concept is public
- Automatable
- no
- Technical impact
- total
- Assessed
- 2mo ago
Exploit prediction
0.69% chance of exploitation in the next 30 days, higher than 53% of all scored CVEs (FIRST EPSS, 2026-11-11).
Exploits and checks
- github.com https://github.com/BomboBombone/CVE-2026-73309 referenced PoC, tagged "exploit" by a source, unverified
- bombobombone.github.io https://bombobombone.github.io/posts/cve-2026-73309/ referenced PoC, tagged "exploit" by a source, unverified
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 4.0 | 9.1 | 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 |
| CNA | 3.1 | 7.4 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N |
| CNA | 4.0 | 9.1 | 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 |
| NVD | 3.1 | 9.1 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N |
Affected products
- XenForo XenForo
Classification
- Weakness
-
- CWE-697 Incorrect Comparison
References
-
xenforo.com
/community/threads/security-fixes-released-for-all-xenforo-and-media-gallery-versions-2-2-0-2-3-12.239856/
vendor-advisory, patch, release-notes
-
github.com
/BomboBombone/CVE-2026-73309
exploit, third-party-advisory
-
bombobombone.github.io
/posts/cve-2026-73309/
technical-description, exploit, third-party-advisory
-
xenforo.com
/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857/
release-notes
-
vulncheck.com
/advisories/xenforo-authentication-bypass-via-oauth2-token-endpoint
third-party-advisory
Sources
- CVE List CVE-2026-73309
- NVD CVE-2026-73309
Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.