Medium severity6.5NVD Advisory· Published Sep 8, 2026· Updated Sep 11, 2026
CVE-2026-73321
CVE-2026-73321
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.
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Affected products
2Patches
Vulnerability mechanics
References
4- bombobombone.github.io/posts/cve-2026-73321/nvdExploitThird Party Advisory
- www.vulncheck.com/advisories/xenforo-uncontrolled-recursion-dos-via-bbcode-parsernvdThird Party Advisory
- xenforo.com/community/threads/security-fixes-released-for-all-xenforo-and-media-gallery-versions-2-2-0-2-3-12.239856/nvdRelease Notes
- xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857/nvdRelease Notes
News mentions
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