CVE-2026-73309CWE-697

CVE-2026-73309

High · published September 8, 2026

CVSS v3.1
7.4
EPSS
1%
Percentile
52.0
In the wild
Unconfirmed
What it is

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.

The record
Technical detail
CVSS v3.1
7.4 · HIGH
Vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N
CVSS v4.0
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
EPSS
0.00685 · 52.0th percentile
Weakness
CWE-697 · Incorrect Comparison
Published
2026-09-08T18:17Z
Affected products (1)
ProductVersionsFixed in
xenforo/xenforo< 2.3.132.3.13
References (5)
https://bombobombone.github.io/posts/cve-2026-73309/ · [email protected]https://github.com/BomboBombone/CVE-2026-73309 · [email protected]https://www.vulncheck.com/advisories/xenforo-authentication-bypass-via-oauth2-token-endpoint · [email protected]https://xenforo.com/community/threads/security-fixes-released-for-all-xenforo-and-media-gallery-versions-2-2-0-2-3-12.239856/ · [email protected]https://xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857/ · [email protected]
EPSS history
Timeline
  • 10 SEP 03:18Z
    EPSS moved — → 0%
    epss
  • 08 SEP 13:15Z
    XenForo < 2.3.13 Authentication Bypass via OAuth2 Token Endpoint
    cvelistv5