CVE-2026-73321

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.

CVSS v3 6.5 MEDIUM

6.5^/10

CVSS v3 : MEDIUM

Vector :

Exploitability : 2.8 / Impact : 3.6

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required LOW

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact NONE

Availability Impact HIGH

Scope UNCHANGED

References

Link	Resource
https://bombobombone.github.io/posts/cve-2026-73321/	Exploit Third Party Advisory
https://github.com/BomboBombone/CVE-2026-73321	Exploit Third Party Advisory
https://www.vulncheck.com/advisories/xenforo-uncontrolled-recursion-dos-via-bbcode-parser	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/	Release Notes
https://xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857/	Release Notes

Configurations

Configuration 1 (hide)

cpe:2.3:a:xenforo:xenforo:*:*:*:*:*:*:*:*

History

No history.

Information

Published : 2026-09-08 14:17

Updated : 2026-09-11 20:30

NVD link : CVE-2026-73321

Mitre link : CVE-2026-73321

CVE.ORG link : CVE-2026-73321

JSON object : View

Products Affected

xenforo

xenforo

CWE

CWE-674

Uncontrolled Recursion

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