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CVE-2026-73309

7.4 · HIGH

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 c…

Published Sep 8, 2026xenforoCWE-697EPSS 0.69%

Overview

CVE-2026-73309 is a high-severity vulnerability affecting xenforo xenforo. It was published on September 8, 2026 and has a CVSS 3.1 base score of 7.4 (HIGH).

This vulnerability has a CVSS 3.1 base score of 7.4, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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.

Remediation

Check the references section for vendor advisories and patches from xenforo. Update xenforo to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

Affected products

VendorProductVersionsStatus
xenforoxenforo>= 0, < 2.3.13Affected

References

Refbombobombone.github.io/posts/cve-2026-73309/GitHubgithub.com/BomboBombone/CVE-2026-73309Refwww.vulncheck.com/advisories/xenforo-authentication-bypass-via-oauth2-token-endpointRefxenforo.com/community/threads/security-fixes-released-for-all-xenforo-and-media-gallery-versions-2-2-0-2-3-12.239856/Refxenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857/

How CyberStrike helps

Frequently asked questions

What is CVE-2026-73309?

CVE-2026-73309 is a high-severity vulnerability affecting xenforo xenforo. It was published on September 8, 2026 and has a CVSS 3.1 base score of 7.4 (HIGH).

How severe is CVE-2026-73309?

This vulnerability has a CVSS 3.1 base score of 7.4, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-73309?

Check the references section for vendor advisories and patches from xenforo. Update xenforo to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-73309?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-73309 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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