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CVE-2026-73321 Details

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.

Metrics

CVSS 3.x Severity and Vector Strings:

CNA: [email protected]CVSS-B:6.5 MEDIUMVector:CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

References to Advisories, Solutions, and Tools

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URL	Source(s)	Tag(s)
https://bombobombone.github.io/posts/cve-2026-73321/	[email protected]	ExploitThird Party Advisory
https://github.com/BomboBombone/CVE-2026-73321	[email protected]	ExploitThird Party Advisory
https://www.vulncheck.com/advisories/xenforo-uncontrolled-recursion-dos-via-bbcode-parser	[email protected]	Third Party Advisory
https://xenforo.com/community/threads/security-fixes-released-for-all-xenforo-and-media-gallery-versions-2-2-0-2-3-12.239856/	[email protected]	Release Notes
https://xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857/	[email protected]	Release Notes

Weakness Enumeration

CWE-ID	CWE Name	Source
CWE-674	Uncontrolled Recursion	[email protected]

Affected Products

Product	Versions
xenforo xenforo	< 2.3.13
CPE cpe:2.3:a:xenforo:xenforo:::::::: Remediation No remediation found in references.

Change History

4 change records found show changes

Date	Action	Recorded By
Sep 11, 2026	Initial Analysis	[email protected]
Sep 10, 2026	CVE Modified	CISA-ADP
Sep 9, 2026	CVE Modified	[email protected]
Sep 8, 2026	New CVE Received	[email protected]