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CVE-2026-73309
XenForo < 2.3.13 Authentication Bypass via OAuth2 Token Endpoint
Critical9.1EPSS 0.69%
- Published
- Updated
- Reserved
- Assigned by
- VulnCheck
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.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| VulnCheckCNA (assigner) | 4.0 | Critical9.1 | 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 |
| VulnCheckCNA (assigner) | 3.1 | High7.4 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N |
| NVDNVD · Analyzed | 4.0 | Critical9.1 | 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 |
- EPSS (exploitation in 30 days)
- 0.69% · top 47% of all CVEs (6 Nov 2026)
- CISA SSVC
- Exploitation: poc · Automatable: no · Technical impact: total
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The list uses the assigner's score when there is one, then CISA's, then NVD's: Critical 9.1.
Weakness
Affected products
References (5)
- Vendor Advisory (opens in a new tab)vendor-advisorypatch
- Release Notes (opens in a new tab)release-notes
- Researcher Advisory (opens in a new tab)technical-description
- Researcher PoC (opens in a new tab)exploit
- https://www.vulncheck.com/advisories/xenforo-authentication-bypass-via-oauth2-token-endpoint (opens in a new tab)third-party-advisory
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://trackcve.app/cve/CVE-2026-73309)Record last updated .