{"id":"CVE-2026-73321","title":"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","summary":"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 craf…","severity":"medium","cvss":6.5,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H","cwe":["CWE-674"],"vendor":"xenforo","product":"xenforo","affected":["xenforo < 2.3.13"],"patched":["xenforo 2.3.13"],"published":"2026-09-08","updated":"2026-09-11","sourceUpdated":"2026-09-11T20:30:18.293","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-73321","references":[{"url":"https://bombobombone.github.io/posts/cve-2026-73321/","label":"disclosure@vulncheck.com"},{"url":"https://github.com/BomboBombone/CVE-2026-73321","label":"disclosure@vulncheck.com"},{"url":"https://www.vulncheck.com/advisories/xenforo-uncontrolled-recursion-dos-via-bbcode-parser","label":"disclosure@vulncheck.com"},{"url":"https://xenforo.com/community/threads/security-fixes-released-for-all-xenforo-and-media-gallery-versions-2-2-0-2-3-12.239856/","label":"disclosure@vulncheck.com"},{"url":"https://xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857/","label":"disclosure@vulncheck.com"}],"tags":["nvd","exploit-available","cve.org"],"epss":0.004,"epssPercentile":0.33993,"exploits":{"github":1,"githubRepos":["https://github.com/BomboBombone/CVE-2026-73321"],"checkedAt":"2026-09-21T15:30:28.951Z"},"exploitAvailable":true,"ssvc":{"exploitation":"poc","automatable":"no","technicalImpact":"partial","timestamp":"2026-09-10T13:49:59.215010Z"},"ingestedAt":"2026-09-08T15:33:26.985Z","slug":"CVE-2026-73321","body":"## Overview\n\nXenForo 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.\n\n## Affected\n\n- `xenforo < 2.3.13`\n\n## Remediation\n\nUpgrade past the affected range:\n\n- `xenforo 2.3.13`","depth":"twilight","depthScore":48,"depthScoreParts":{"impact":35.8,"likelihood":0.1,"exploitation":12,"ransomware":0},"changes":[{"seq":8360,"id":"CVE-2026-73321","ts":1788920417556,"field":"exploit_available","old":"false","new":"true"}]}