CVE-2026-73309

9.1 CRITICAL 0.7% exploit odds No fix listed Auth & access Web app

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.

At a glance

Exploitability: Can be exploited over the network without logging in. High risk of data exposure, data tampering.
Exploit odds: 0.7% chance of exploitation in the next 30 days (EPSS).
Fix: No patch or advisory is linked yet. Look at mitigations or restrict exposure.

Timeline

2026-08-11 19:56 UTC ReservedThe CVE id was reserved by its CNA
2026-09-08 14:17 UTC PublishedDisclosed publicly on CVE.org and NVD
2026-09-11 20:33 UTC Last updatedMost recent change to the record

Why it ranks here

Exploited in the wild: no, CISA does not list it.
Exploit odds: 0.7% in the next 30 days (EPSS).
Severity: 9.1 CRITICAL (CVSS).
Fix: none linked yet, which raises it.

Details

Published: 2026-09-08 14:17 UTC
Last modified: 2026-09-11 20:33 UTC
Exploit probability: 0.7% · EPSS, next 30 days
Weakness: CWE-697
Record status: Analyzed

Affected

Xenforo < 2.3.13

Attack profile CVSS 4.0 · 9.1

Attack vector: Network
Complexity: High
Attack requirements: None
Privileges needed: None
User interaction: None
Confidentiality: High
Integrity: High
Availability: None

Raw vector

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

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2026-73309.md and follow it. Check whether this project is affected by CVE-2026-73309. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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References

NVD record · CVE.org record