CVE-2026-73321

MEDIUMPre-NVD 6.56.5—
EchelonGraph scoreHIGH confidence

Score 6.5 from GitHub Security Advisory (severity: HIGH) published 2026-09-08. a secondary CVSS source baseline 6.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 3 sources updated this weekElevated
6.5EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 6.5Exploit: Elevated riskExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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 v3
6.5
EG Score
6.5(high)
EG Risk
45(Track)
EG Risk 45/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity65% × 45%
Exploitation40% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
34%
KEV
Not listed

Published

September 8, 2026

Last Modified

September 11, 2026

Advisory Details (1)

Auto-updated Sep 8, 2026
No patch confirmed yet.
generic

XenForo < 2.3.13 Uncontrolled Recursion DoS via BBCode Parser | Advisories | VulnCheck

https://www.vulncheck.com/advisories/xenforo-uncontrolled-recursion-dos-via-bbcode-parser

Vendor Advisories for CVE-2026-73321(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 17× in last 7d / 36× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-09-18 21:21 UTCEG score recompute
  2. 2026-09-18 21:21 UTCGHSA enrichment
  3. 2026-09-18 19:28 UTCEPSS rescore
  4. 2026-09-17 21:18 UTCEG score recompute
  5. 2026-09-17 21:18 UTCGHSA enrichment
  6. 2026-09-16 21:17 UTCEG score recompute
  7. 2026-09-16 21:17 UTCGHSA enrichment
  8. 2026-09-16 14:08 UTCEPSS rescore
  9. 2026-09-16 05:15 UTCEPSS rescore
  10. 2026-09-15 20:51 UTCEG score recompute
  11. 2026-09-15 20:51 UTCGHSA enrichment
  12. 2026-09-15 03:12 UTCEPSS rescore
  13. 2026-09-14 20:50 UTCGHSA enrichment
  14. 2026-09-13 20:49 UTCEG score recompute
  15. 2026-09-13 20:49 UTCGHSA enrichment
  16. 2026-09-12 20:48 UTCEG score recompute
  17. 2026-09-12 20:48 UTCGHSA enrichment
  18. 2026-09-12 15:02 UTCEPSS rescore
  19. 2026-09-11 20:47 UTCGHSA enrichment
  20. 2026-09-11 16:25 UTCEG score recompute
  21. 2026-09-11 16:25 UTCGHSA enrichment
  22. 2026-09-11 14:53 UTCEPSS rescore
  23. 2026-09-10 16:24 UTCEG score recompute
  24. 2026-09-10 16:24 UTCGHSA enrichment
  25. 2026-09-10 15:27 UTCEG score recompute
Show 11 more
  1. 2026-09-10 15:27 UTCGHSA enrichment
  2. 2026-09-10 09:35 UTCEPSS rescore
  3. 2026-09-10 01:18 UTCEG score recompute
  4. 2026-09-10 01:18 UTCGHSA enrichment
  5. 2026-09-09 01:18 UTCEG score recompute
  6. 2026-09-09 01:18 UTCGHSA enrichment
  7. 2026-09-08 20:11 UTCEG score recompute
  8. 2026-09-08 20:11 UTCGHSA enrichment
  9. 2026-09-08 14:29 UTCEG score recompute
  10. 2026-09-08 13:25 UTCEG score recompute
  11. 2026-09-08 13:24 UTCMITRE cvelistV5first tracked

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-73321?
CVE-2026-73321 is a medium vulnerability published on September 8, 2026. 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…
When was CVE-2026-73321 disclosed?
CVE-2026-73321 was first published in the National Vulnerability Database on September 8, 2026, with the most recent update on September 11, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-73321 actively exploited?
CVE-2026-73321 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 65.9% of all scored CVEs.
What is the CVSS score of CVE-2026-73321?
CVE-2026-73321 has a CVSS v3 base score of 6.5 (NVD).
How do I remediate CVE-2026-73321?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-73321, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

Explore the affected products and dependency analysis for CVE-2026-73321

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