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TI-2026-51434 Aliases CVE-2026-73309GHSA-pr5w-fh2v-7c9q

XenForo < 2.3.13 Authentication Bypass via OAuth2 Token Endpoint

Priority HIGH 74CWE-697Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
High
Attack requirements
None
Impact type
—
Confidentiality · integrity · availability
High · High · None
Fix status
Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA.

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.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00685 52nd percentileScored 2026-11-07
Public exploit Yes 2 exploit referencesTagged by NVD and the CNA
Fix Fixed XenForo (XenForo): 2.3.13

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
No
Technical impact
Total

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
XenForoXenForobefore 2.3.132.3.13Patch availableCNA
  • XenForo VendorXenForo Affected before 2.3.13 Fixed in 2.3.13 Patch available CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:xenforo:xenforo:*:*:*:*:*:*:*:*before 2.3.13VulnerableXenForo
  • cpe:2.3:a:xenforo:xenforo:*:*:*:*:*:*:*:* Versions before 2.3.13 Vulnerable ·XenForo

Remediation

  • Fix · CNA XenForo (XenForo) Fixed in 2.3.13

Fixed in the same release

Records fixed by the same vendor advisory or release, as the CNA lists them.

  • Advisory ·

    XenForo — xenforo.com/community/threads/security-fixes-released-for-a…

    14 records Highest priority Priority HIGH 4 HIGH, 5 MEDIUM, 5 LOW

    Other records, highest priority first

    • TI-2026-51441 XenForo < 2.3.13 Payment Replay via PayPal REST Payment ProviderPriority HIGH 77
    • TI-2026-51439 XenForo < 2.3.13 Signature Verification Bypass via PayPal REST WebhookPriority HIGH 77
    • TI-2026-51436 XenForo < 2.3.13 OAuth2 Authorization Code ReusePriority HIGH 74
    Show all 14 records → Advisory →

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-73309
  2. 2026-10-03 Alias added: GHSA-pr5w-fh2v-7c9q

References

Exploit 2

Patch 1

Other 1

  • TI-2026-51441 XenForo < 2.3.13 Payment Replay via PayPal REST Payment Provider CVSS 4.0HIGH 8.7
  • TI-2026-51439 XenForo < 2.3.13 Signature Verification Bypass via PayPal REST Webhook CVSS 4.0HIGH 8.7
  • TI-2026-51436 XenForo < 2.3.13 OAuth2 Authorization Code Reuse CVSS 4.0CRITICAL 9.1
  • TI-2024-25701 Xenforo before 2.2.16 allows code injection. CVSS 3.1HIGH 8.8
  • TI-2026-51446 XenForo < 2.3.13 Uncontrolled Recursion DoS via BBCode Parser CVSS 4.0HIGH 7.1
  • TI-2026-51444 XenForo < 2.3.13 XSS via Dynamic Redirect Handler CVSS 4.0MEDIUM 5.1
See all 27 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences