CVE-2026-73309

CRITICALNVD 9.19.1—
EchelonGraph scoreMEDIUM confidence

This critical-severity CVE scores 9.1 under NVD CVSS v3. EPSS exploit probability: 0.5%, top 60% of all CVEs by exploit prediction. GitHub Security Advisory enrichment pending alignment with NVD CVSS.

Triggered by: NVD CVSS baseline
Sources: epss, ghsa, nvd
Trending — 3 sources updated this weekElevated
9.1EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 9.1Exploit: 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 authentication bypass vulnerability in the OAuth2 token endpoint that allows unauthenticated attackers to obtain valid token pairs by submitting empty values for client_secret and code_verifier parameters. Attackers can exploit PHP truthy evaluation logic, which treats empty strings as false and skips client secret validation and PKCE code verifier validation, to exchange a valid authorization code for a token pair without proving client identity or holding the PKCE commitment.

CVSS v3
9.1
EG Score
9.1(medium)
EG Risk
57(Track*)
EG Risk 57/100SSVC: 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
Severity91% × 45%
Exploitation40% × 40%
Automatability0% × 15%
Action: Watch closely — could escalate to Attend.
EPSS PROB
0%
EPSS %ILE
40%
KEV
Not listed

Published

September 8, 2026

Last Modified

September 11, 2026

Advisory Details (3)

Auto-updated Sep 15, 2026
🔬 Proof of concept available. No patch confirmed yet.
generic

XenForo < 2.3.13 Authentication Bypass via OAuth2 Token Endpoint | Advisories | VulnCheck

https://www.vulncheck.com/advisories/xenforo-authentication-bypass-via-oauth2-token-endpoint
generic🟡 PoC Available

GitHub - BomboBombone/CVE-2026-73309: Sanitized XenForo write-up and proof of concept for CVE-2026-73309. · GitHub

https://github.com/BomboBombone/CVE-2026-73309
generic

CVE-2026-73309: Empty OAuth2 credentials bypass — BomboBombone

https://bombobombone.github.io/posts/cve-2026-73309/

Vendor Advisories for CVE-2026-73309(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 50× in last 7d / 77× 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. 2026-09-19 15:09 UTCGHSA enrichment
  2. 2026-09-19 10:46 UTCGHSA enrichment
  3. 2026-09-19 06:31 UTCGHSA enrichment
  4. 2026-09-19 02:15 UTCGHSA enrichment
  5. 2026-09-18 21:55 UTCEG score recompute
  6. 2026-09-18 21:55 UTCGHSA enrichment
  7. 2026-09-18 19:28 UTCEPSS rescore
  8. 2026-09-18 17:40 UTCGHSA enrichment
  9. 2026-09-18 13:24 UTCGHSA enrichment
  10. 2026-09-18 09:06 UTCGHSA enrichment
  11. 2026-09-18 04:50 UTCGHSA enrichment
  12. 2026-09-18 00:35 UTCGHSA enrichment
  13. 2026-09-17 20:19 UTCEG score recompute
  14. 2026-09-17 20:19 UTCGHSA enrichment
  15. 2026-09-17 15:48 UTCGHSA enrichment
  16. 2026-09-17 11:32 UTCGHSA enrichment
  17. 2026-09-17 07:16 UTCGHSA enrichment
  18. 2026-09-17 02:57 UTCGHSA enrichment
  19. 2026-09-16 22:34 UTCGHSA enrichment
  20. 2026-09-16 18:18 UTCEG score recompute
  21. 2026-09-16 18:18 UTCGHSA enrichment
  22. 2026-09-16 14:08 UTCEPSS rescore
  23. 2026-09-16 13:55 UTCGHSA enrichment
  24. 2026-09-16 08:58 UTCEG score recompute
  25. 2026-09-16 08:58 UTCGHSA enrichment
Show 52 more
  1. 2026-09-16 05:15 UTCEPSS rescore
  2. 2026-09-16 03:35 UTCGHSA enrichment
  3. 2026-09-15 23:19 UTCGHSA enrichment
  4. 2026-09-15 18:41 UTCGHSA enrichment
  5. 2026-09-15 14:23 UTCGHSA enrichment
  6. 2026-09-15 10:07 UTCGHSA enrichment
  7. 2026-09-15 05:51 UTCEG score recompute
  8. 2026-09-15 05:51 UTCGHSA enrichment
  9. 2026-09-15 03:12 UTCEPSS rescore
  10. 2026-09-15 01:35 UTCGHSA enrichment
  11. 2026-09-14 21:19 UTCGHSA enrichment
  12. 2026-09-14 17:03 UTCGHSA enrichment
  13. 2026-09-14 12:47 UTCGHSA enrichment
  14. 2026-09-14 08:31 UTCGHSA enrichment
  15. 2026-09-14 04:15 UTCGHSA enrichment
  16. 2026-09-14 00:00 UTCGHSA enrichment
  17. 2026-09-13 19:44 UTCEG score recompute
  18. 2026-09-13 19:44 UTCGHSA enrichment
  19. 2026-09-13 15:28 UTCGHSA enrichment
  20. 2026-09-13 11:12 UTCGHSA enrichment
  21. 2026-09-13 06:56 UTCGHSA enrichment
  22. 2026-09-13 02:41 UTCGHSA enrichment
  23. 2026-09-12 22:25 UTCGHSA enrichment
  24. 2026-09-12 18:07 UTCEG score recompute
  25. 2026-09-12 18:07 UTCGHSA enrichment
  26. 2026-09-12 15:02 UTCEPSS rescore
  27. 2026-09-12 13:51 UTCGHSA enrichment
  28. 2026-09-12 09:35 UTCGHSA enrichment
  29. 2026-09-12 05:19 UTCGHSA enrichment
  30. 2026-09-12 01:03 UTCGHSA enrichment
  31. 2026-09-11 20:47 UTCEG score recompute▲ 1.70
  32. 2026-09-11 20:47 UTCGHSA enrichment
  33. 2026-09-11 20:35 UTCNVD updateCVSS v3 → 9.1 · severity → CRITICAL
  34. 2026-09-11 14:53 UTCEPSS rescore
  35. 2026-09-11 08:34 UTCGHSA enrichment
  36. 2026-09-10 19:34 UTCEG score recompute
  37. 2026-09-10 19:34 UTCGHSA enrichment
  38. 2026-09-10 09:35 UTCEPSS rescore
  39. 2026-09-10 06:34 UTCGHSA enrichment
  40. 2026-09-09 17:34 UTCEG score recompute
  41. 2026-09-09 17:34 UTCGHSA enrichment
  42. 2026-09-09 16:52 UTCEG score recompute
  43. 2026-09-09 16:51 UTCGHSA enrichment
  44. 2026-09-09 14:18 UTCEG score recompute
  45. 2026-09-09 14:18 UTCGHSA enrichment
  46. 2026-09-09 01:18 UTCEG score recompute
  47. 2026-09-09 01:18 UTCGHSA enrichment
  48. 2026-09-08 20:12 UTCEG score recompute
  49. 2026-09-08 20:12 UTCGHSA enrichment
  50. 2026-09-08 14:31 UTCEG score recompute
  51. 2026-09-08 13:26 UTCEG score recompute
  52. 2026-09-08 13:24 UTCMITRE cvelistV5first tracked

Frequently asked(5)

What is CVE-2026-73309?
CVE-2026-73309 is a critical vulnerability published on September 8, 2026. XenForo before 2.3.13 contains an authentication bypass vulnerability in the OAuth2 token endpoint that allows unauthenticated attackers to obtain valid token pairs by submitting empty values for clientsecret and codeverifier parameters. Attackers can exploit PHP truthy evaluation logic, which…
When was CVE-2026-73309 disclosed?
CVE-2026-73309 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-2026-73309 actively exploited?
CVE-2026-73309 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 59.7% of all scored CVEs.
What is the CVSS score of CVE-2026-73309?
CVE-2026-73309 has a CVSS v3 base score of 9.1 (NVD).
How do I remediate CVE-2026-73309?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-73309, 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-2026-73309

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