CVE-2026-84504

HIGHPre-NVD 8.18.1—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 8.1 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.4%, top 66% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, secondary
8.1EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 8.1Exploit: None knownExposed: 0

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

fastify versions before 5.12.2 treat the object resolved by a successful Ajv async validator as the value result protocol used by custom validator compilers. If a request that passes its route schema contains a property named value at the root, fastify replaces the entire request body with that property's value before the handler runs, so the handler receives a different object than the one that satisfied the schema. An authenticated low-privilege caller can use this to make nested data replace the validated body and trigger an operation the route schema did not authorize, leading to unauthorized state changes and data disclosure. Users should upgrade to fastify 5.12.2 or later.

CVSS v3
8.1
EG Score
8.1(medium)
EG Risk
37(Track)
EG Risk 37/100SSVC: 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
Severity81% × 45%
Exploitation0% × 40%
Automatability0% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
34%
KEV
Not listed

Published

September 4, 2026

Last Modified

September 15, 2026

Advisory Details (2)

Auto-updated Sep 4, 2026
Patch available. Sources: github.
generic

Security Advisories | OpenJS Foundation CVE Numbering Authority

https://cna.openjsf.org/security-advisories.html
github Patch Available

fastify vulnerable to request body replacement via an async validation result collision · Advisory · fastify/fastify · GitHub

https://github.com/fastify/fastify/security/advisories/GHSA-667r-xxjv-c9mm

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 13× in last 7d / 40× 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. 2026-09-24 22:25 UTCEG score recompute
  2. 2026-09-24 14:04 UTCEPSS rescore
  3. 2026-09-23 23:47 UTCEG score recompute
  4. 2026-09-23 17:54 UTCEPSS rescore
  5. 2026-09-23 01:07 UTCEG score recompute
  6. 2026-09-22 16:01 UTCEPSS rescore
  7. 2026-09-22 02:27 UTCEG score recompute
  8. 2026-09-21 21:09 UTCEPSS rescore
  9. 2026-09-21 03:44 UTCEG score recompute
  10. 2026-09-20 20:16 UTCEPSS rescore
  11. 2026-09-19 17:44 UTCEG score recompute
  12. 2026-09-19 06:24 UTCEG score recompute
  13. 2026-09-18 19:28 UTCEPSS rescore
  14. 2026-09-17 20:25 UTCEG score recompute
  15. 2026-09-17 19:32 UTCEPSS rescore
  16. 2026-09-16 18:55 UTCEG score recompute
  17. 2026-09-16 14:09 UTCEPSS rescore
  18. 2026-09-16 07:32 UTCEG score recompute
  19. 2026-09-16 05:15 UTCEPSS rescore
  20. 2026-09-15 10:59 UTCEG score recompute
  21. 2026-09-15 03:12 UTCEPSS rescore
  22. 2026-09-15 03:12 UTCEPSS rescore
  23. 2026-09-14 00:45 UTCEG score recompute
  24. 2026-09-13 02:07 UTCEG score recompute
  25. 2026-09-11 16:08 UTCEG score recompute
Show 15 more
  1. 2026-09-11 14:53 UTCEPSS rescore
  2. 2026-09-11 14:53 UTCEPSS rescore
  3. 2026-09-10 17:22 UTCEG score recompute
  4. 2026-09-09 07:17 UTCEG score recompute
  5. 2026-09-08 22:01 UTCEPSS rescore
  6. 2026-09-08 02:06 UTCEG score recompute
  7. 2026-09-06 14:47 UTCEG score recompute
  8. 2026-09-06 13:48 UTCEPSS rescore
  9. 2026-09-05 16:07 UTCEG score recompute
  10. 2026-09-05 15:31 UTCEPSS rescore
  11. 2026-09-04 17:28 UTCEG score recompute
  12. 2026-09-04 16:39 UTCEG score recompute
  13. 2026-09-04 10:31 UTCEG score recompute
  14. 2026-09-04 09:49 UTCEG score recompute
  15. 2026-09-04 09:48 UTCMITRE cvelistV5first tracked

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-84504?
CVE-2026-84504 is a high vulnerability published on September 4, 2026. fastify versions before 5.12.2 treat the object resolved by a successful Ajv async validator as the value result protocol used by custom validator compilers. If a request that passes its route schema contains a property named value at the root, fastify replaces the entire request body with that…
When was CVE-2026-84504 disclosed?
CVE-2026-84504 was first published in the National Vulnerability Database on September 4, 2026, with the most recent update on September 15, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-84504 actively exploited?
CVE-2026-84504 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 65.6% of all scored CVEs.
What is the CVSS score of CVE-2026-84504?
CVE-2026-84504 has a CVSS v3 base score of 8.1 (NVD).
How do I remediate CVE-2026-84504?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-84504, 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.

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