XenForo < 2.3.13 Uncontrolled Recursion DoS via BBCode Parser
41Vexday Risk Score
No sign of exploitation. It has a public proof of concept.
ssvc Attendcvss 7.1epss 0.4%
exploitation probability
0.4%top 66% of all CVEs
observed exploitation
nono source reports it
1 public exploit(s)
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:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
Affected products
XenForo · XenForopublic PoCs found — 1
cve_referencegithub.com/BomboBombone/CVE-2026-73321★ 0⚠ Public resources, to assess the exposure of systems you control or are authorized to test. Test only with authorization.
References
https://bombobombone.github.io/posts/cve-2026-73321/https://github.com/BomboBombone/CVE-2026-73321https://www.vulncheck.com/advisories/xenforo-uncontrolled-recursion-dos-via-bbcode-parserhttps://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/