CVE-2026-73321 json
XenForo < 2.3.13 Uncontrolled Recursion DoS via BBCode Parser
published 2mo ago modified last mo. also EUVD-2026-72758
- cvss
- 6.5
- version 3.1, CNA
- cisa kev
- Not listed
- not in CISA's catalog
- epss
- 0.6%
- EPSS 0.6% chance of exploitation in 30 days, percentile 49%
- public exploits
- 0
- none known
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 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.
Patch / fix
- XenForo XenForo 2.3.13
Is CVE-2026-73321 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.
Check with FencerCISA SSVC
- Exploitation
- Proof of concept is public
- Automatable
- no
- Technical impact
- partial
- Assessed
- 2mo ago
Exploit prediction
0.61% chance of exploitation in the next 30 days, higher than 49% of all scored CVEs (FIRST EPSS, 2026-11-11).
Exploits and checks
- github.com https://github.com/BomboBombone/CVE-2026-73321 referenced PoC, tagged "exploit" by a source, unverified
- bombobombone.github.io https://bombobombone.github.io/posts/cve-2026-73321/ referenced PoC, tagged "exploit" by a source, unverified
CVSS scores
| assigned by | version | score | vector |
|---|---|---|---|
| CNA | 4.0 | 7.1 | 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 |
| CNA | 3.1 | 6.5 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H |
| CNA | 4.0 | 7.1 | 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X |
Affected products
- XenForo XenForo
Classification
- Weakness
-
- CWE-674 Uncontrolled Recursion
References
-
xenforo.com
/community/threads/security-fixes-released-for-all-xenforo-and-media-gallery-versions-2-2-0-2-3-12.239856/
vendor-advisory, patch, release-notes
-
github.com
/BomboBombone/CVE-2026-73321
exploit, third-party-advisory
-
bombobombone.github.io
/posts/cve-2026-73321/
technical-description, exploit, third-party-advisory
-
xenforo.com
/community/threads/xenforo-2-3-13-and-add-ons-released-includes-security-fixes.239857/
release-notes
-
vulncheck.com
/advisories/xenforo-uncontrolled-recursion-dos-via-bbcode-parser
third-party-advisory
Sources
- CVE List CVE-2026-73321
- NVD CVE-2026-73321
Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.