CVE-2026-73321
mediumpriority · track · 36EPSS 0.006 · 49 %ileexploit · PoCUSEPSS · scored 2026-10-28
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
Technical severity, 0–10. One row per scoring source.
base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · medium–high · 5.7–7.1
ssvc
A stakeholder decision — act, attend, or track — from exploitation and impact.
weaknesses
The CWE weakness classes this flaw belongs to.
exploits (1)
Public proof-of-concept and weaponised exploit code.
affected products (1)
Products and version ranges known to be affected.
sources
Which sources assert this record, and when.
references (5) nvd
External citations — patches, advisories, analysis.
- https://bombobombone.github.io/posts/cve-2026-73321/ExploitThird Party Advisory
- https://github.com/BomboBombone/CVE-2026-73321ExploitThird Party Advisory
- https://www.vulncheck.com/advisories/xenforo-uncontrolled-recursion-dos-via-bbcode-parserThird Party Advisory
- https://xenforo.com/community/threads/security-fixes-released-for-all-xenforo-and-media-gallery-versions-2-2-0-2-3-12.239856/Release Notes
- https://xenforo.com/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857/Release Notes
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