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.
Scoring
- Severity
- HIGH
- CVSS base score
- 7.1
- CVSS vector
- CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- EPSS probability
- 0.38%
- CWE
- CWE-674
- Published
- 2026-09-08
- Last modified
- 2026-09-09
Affected products
- XenForo XenForo
Weakness type
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