6.5mediumMedium
CVE-2026-73321
Xenforo Xenforo
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.
Exploitation status
- Published references include exploit or proof-of-concept material. There is no confirmation it is being used in real attacks.
What the metrics mean
- It is reachable over a network, without needing local access.
- For an attacker who can reach it, no special conditions are needed to exploit it.
- To exploit it, an ordinary user account is needed.
- Beyond that, no action by a user is required.
Scoring
- CVSS
- 6.5 (v3.1)
- Vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H- CVSS v4
- 7.1
- Weakness
- CWE-674
- Assigned by
- disclosure@vulncheck.com
Dates
- Published
- 2026-09-08
- Last modified
- 2026-09-11
- Sources
- NVD
Affected products
- Xenforo Xenforo- 2.3.13
As listed in the NVD configuration data. Not a statement about your estate.
References
- https://bombobombone.github.io/posts/cve-2026-73321/
- https://github.com/BomboBombone/CVE-2026-73321
- https://www.vulncheck.com/advisories/xenforo-uncontrolled-recursion-dos-via-bbcode-parser
- https://xenforo.com/community/threads/security-fixes-released-for-all-xenforo-and-media-gallery-versions-2-2-0-2-3-12.239856/
- https://xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857/