CVE-2026-18504

MEDIUMNVD 5.35.3
EchelonGraph scoreMEDIUM confidence

“—” beside the score: it is equal to NVD's CVSS score.

This medium-severity CVE scores 5.3 under NVD CVSS v3. EPSS exploit probability: 0.3% (22nd percentile of EPSS-scored CVEs). No GitHub Security Advisory CVSS is on record for this CVE.

Triggered by: Headline CVSS from NVD CVSS v3
Sources: EPSS, NVD CVSS v3
5.3EG
EchelonGraph verdictMonitorRemediate within your standard update timelines (the SSVC decision on this page).
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0.3%CVSS: 5.3Exploit: None knownExposed services: Not assessed

A fix is available — apply it.

fastify is a fast and low overhead web framework for Node.js. Versions of fastify before 5.12.1 are affected by a schema validation bypass when a request body schema targets a root primitive value. When the schema validates a top-level primitive such as an integer, Ajv can coerce a JSON string into the expected type during validation, but Fastify does not replace the root request body with the coerced value, so the route handler receives the original unvalidated string. As a result, a request that should have failed validation can reach application logic with a value that does not satisfy the schema, which can undermine integrity and access-control checks that rely on the validated type. Users should upgrade to fastify 5.12.1, which fixes the mismatch. No known workarounds are available.

CVSS v3
5.3
EG Score
5.3MEDIUMmedium confidence
EG Risk
24
EG Risk 24/100

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 (value × EchelonGraph’s weight)
Severity53% × 45%
The EG Score, 5.3 of 10.
Exploitation0.3% × 40%
FIRST EPSS: the 30-day exploitation probability when EchelonGraph scored this CVE.
Automatability0% × 15%
CISA's SSVC Automatable value: no (Vulnrichment).
SSVC (CISA's decision table, applied by EchelonGraph): Track at every mission impact level.
Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.
Action: A fix is available. Apply it within your standard update timelines.
EPSS PROB
0.3%
EPSS %ILE
22nd
KEV
Not listed

SSVC (CISA's decision table, applied by EchelonGraph)Track at every mission impact level.

A fix is available. Apply it within your standard update timelines.

Exploitation none (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

BOD 26-04 (CISA's remediation timeline, Table 1)60 days if the affected system is publicly exposed; Fix on system upgrade if it is not.

In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact partial (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

Published

August 18, 2026

Last Modified

September 2, 2026

Advisory Details (2)

Auto-updated Aug 18, 2026
Patch available. Sources: github.
Web page

Security Advisories | OpenJS Foundation CVE Numbering Authority

https://cna.openjsf.org/security-advisories.html
GitHub advisoryMentions a patch (unverified)

fastify vulnerable to schema validation bypass via root primitive coercion mismatch · Advisory · fastify/fastify · GitHub

https://github.com/fastify/fastify/security/advisories/GHSA-w2qp-rph6-63g4

Vendor Advisories for CVE-2026-18504(1)

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

Affected Packages

(1 across 1 ecosystem)
npm(1)
PackageVulnerable rangeFix by version rangeDependents
fastify—
  • every version up to 5.12.1: fixed in 5.12.1
—

Weakness Classification(1)

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

Data Freshness Timeline

(refreshed 11× in last 7d / 41× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. 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. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.

  1. 2026-10-13 16:33 UTCEPSS rescoreEPSS 0.3% · 22nd percentile
  2. 2026-10-12 16:33 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  3. 2026-10-12 16:27 UTCEG score recompute
  4. 2026-10-11 20:07 UTCEG score recompute
  5. 2026-10-11 17:20 UTCEG score recompute
  6. 2026-10-11 14:52 UTCEG score recompute
  7. 2026-10-11 13:48 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  8. 2026-10-10 19:59 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  9. 2026-10-09 20:06 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  10. 2026-10-08 17:11 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  11. 2026-10-07 23:47 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  12. 2026-10-07 11:10 UTCEG score recompute
  13. 2026-10-06 15:17 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  14. 2026-10-06 08:21 UTCEG score recompute
  15. 2026-10-05 17:42 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  16. 2026-10-04 23:21 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  17. 2026-10-03 17:37 UTCEG score recompute
  18. 2026-10-03 14:25 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  19. 2026-10-02 15:05 UTCEG score recompute
  20. 2026-10-01 19:49 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  21. 2026-10-01 10:45 UTCEG score recompute
  22. 2026-09-30 15:02 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  23. 2026-09-30 09:47 UTCEG score recompute
  24. 2026-09-29 15:20 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  25. 2026-09-28 13:51 UTCEPSS rescoreEPSS 0.3% · 21st percentile
Show 65 more
  1. 2026-09-28 08:41 UTCEG score recompute
  2. 2026-09-27 13:47 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  3. 2026-09-27 07:54 UTCEG score recompute
  4. 2026-09-26 15:58 UTCEPSS rescoreEPSS 0.3% · 21st percentile
  5. 2026-09-25 01:24 UTCEG score recompute
  6. 2026-09-22 20:24 UTCEG score recompute
  7. 2026-09-21 15:46 UTCEG score recompute
  8. 2026-09-20 14:01 UTCEG score recompute
  9. 2026-09-19 12:32 UTCEG score recompute
  10. 2026-09-18 19:27 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
  11. 2026-09-18 11:44 UTCEG score recompute
  12. 2026-09-17 10:56 UTCEG score recompute
  13. 2026-09-16 14:07 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
  14. 2026-09-16 10:07 UTCEG score recompute
  15. 2026-09-16 05:14 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
  16. 2026-09-15 08:15 UTCEG score recompute
  17. 2026-09-14 07:27 UTCEG score recompute
  18. 2026-09-13 16:46 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
  19. 2026-09-13 06:39 UTCEG score recompute
  20. 2026-09-12 15:00 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
  21. 2026-09-12 05:51 UTCEG score recompute
  22. 2026-09-11 14:52 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
  23. 2026-09-11 09:36 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
  24. 2026-09-11 05:03 UTCEG score recompute
  25. 2026-09-10 09:34 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
  26. 2026-09-09 03:22 UTCEG score recompute
  27. 2026-09-08 22:00 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
  28. 2026-09-07 19:21 UTCEG score recompute
  29. 2026-09-07 16:01 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
  30. 2026-09-06 18:33 UTCEG score recompute
  31. 2026-09-06 13:47 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
  32. 2026-09-05 17:45 UTCEG score recompute
  33. 2026-09-04 16:55 UTCEG score recompute
  34. 2026-09-04 05:06 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
  35. 2026-09-02 14:46 UTCEG score recompute▼ 0.10
  36. 2026-09-02 14:43 UTCNVD updateCVSS v3 → 5.3
  37. 2026-09-02 14:11 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
  38. 2026-09-01 23:11 UTCEG score recompute
  39. 2026-09-01 13:53 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
  40. 2026-09-01 04:39 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
  41. 2026-08-30 21:35 UTCEG score recompute
  42. 2026-08-30 19:17 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
  43. 2026-08-30 01:22 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
  44. 2026-08-29 20:47 UTCEG score recompute
  45. 2026-08-28 21:41 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
  46. 2026-08-27 20:59 UTCEG score recompute
  47. 2026-08-27 14:25 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
  48. 2026-08-26 20:11 UTCEG score recompute
  49. 2026-08-26 14:46 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
  50. 2026-08-25 19:14 UTCEG score recompute
  51. 2026-08-25 13:48 UTCEPSS rescoreEPSS 0.3% · 23rd percentile
  52. 2026-08-24 18:26 UTCEG score recompute
  53. 2026-08-23 17:38 UTCEG score recompute
  54. 2026-08-23 00:19 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  55. 2026-08-22 16:51 UTCEG score recompute
  56. 2026-08-21 23:49 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  57. 2026-08-21 16:03 UTCEG score recompute
  58. 2026-08-20 22:55 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  59. 2026-08-20 15:15 UTCEG score recompute
  60. 2026-08-19 17:03 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  61. 2026-08-19 14:27 UTCEG score recompute
  62. 2026-08-19 13:41 UTCEG score recompute
  63. 2026-08-18 21:36 UTCEG score recompute
  64. 2026-08-18 20:33 UTCEG score recomputeFirst assessed: 5.4 MEDIUM
  65. 2026-08-18 20:33 UTCMITRE cvelistV5first tracked

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Frequently asked(5)

What is CVE-2026-18504?
CVE-2026-18504 is a medium-severity vulnerability; its CVE record was published on August 18, 2026. fastify is a fast and low overhead web framework for Node.js. Versions of fastify before 5.12.1 are affected by a schema validation bypass when a request body schema targets a root primitive value. When the schema validates a top-level primitive such as an integer, Ajv can coerce a JSON string into…
When was the CVE record for CVE-2026-18504 published?
The CVE record for CVE-2026-18504 was published on August 18, 2026. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of September 2, 2026; the record at its source may have been updated since.
Is CVE-2026-18504 actively exploited?
CVE-2026-18504 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.3% probability of exploitation in the next 30 days (22nd percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-18504?
CVE-2026-18504 has a CVSS v3 base score of 5.3 (NVD).
How do I remediate CVE-2026-18504?
A fix for CVE-2026-18504 is available: update to the fixed version the vendor names in its advisory. The vendor advisories EchelonGraph has for CVE-2026-18504 are linked in the Vendor Advisories panel on this page.

Dependency Blast Radius

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