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CVE-2026-73321

6.5 · MEDIUM

XenForo before 2.3.13 contains an uncontrolled recursion vulnerability in the BBCode parser that allows authenticated attackers to cause persistent denial of service by submitting a post with deepl…

Published Sep 8, 2026xenforoCWE-674EPSS 0.61%

Overview

CVE-2026-73321 is a medium-severity vulnerability affecting xenforo xenforo. It was published on September 8, 2026 and has a CVSS 3.1 base score of 6.5 (MEDIUM).

This vulnerability has a CVSS 3.1 base score of 6.5, rated MEDIUM. It can be exploited remotely over the network. Some level of privileges is required for exploitation.

Technical description

XenForo before 2.3.13 contains an uncontrolled recursion vulnerability in the BBCode parser that allows authenticated attackers to cause persistent denial of service by submitting a post with deeply nested BBCode tags. Attackers can craft a single malicious post with sufficient nesting depth to exceed PHP's stack limit, causing fatal errors that repeatedly terminate PHP-FPM workers for all visitors rendering the affected thread.

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-2026-73321/GitHubgithub.com/BomboBombone/CVE-2026-73321Refwww.vulncheck.com/advisories/xenforo-uncontrolled-recursion-dos-via-bbcode-parserRefxenforo.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-2026-73321?

CVE-2026-73321 is a medium-severity vulnerability affecting xenforo xenforo. It was published on September 8, 2026 and has a CVSS 3.1 base score of 6.5 (MEDIUM).

How severe is CVE-2026-73321?

This vulnerability has a CVSS 3.1 base score of 6.5, rated MEDIUM. It can be exploited remotely over the network. Some level of privileges is required for exploitation.

How do I fix or remediate CVE-2026-73321?

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-2026-73321?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-73321 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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