fastify vulnerable to schema validation bypass via root primitive coercion mismatch — GHSA-W2QP-RPH6-63G4

Summary

### Impact `fastify` before 5.12.1, when a route uses a root-level primitive body schema (for example an integer with a minimum and maximum) and the default type coercion, validates the coerced value but exposes the original, uncoerced value to the route handler. For example, a JSON body `"10"` is coerced to the number `10` and passes an integer 1 to 10 schema, but `request.body` stays the string `"10"`. An…

Timeline

Published by source

2026-09-02

Risk context

• Reported severity or threat level: medium.
• Reported CVSS score: 5.4 out of 10.
• Reported EPSS value: 0.00312.
• Review exposure for the affected product or family: npm: fastify.

Product

npm: fastify

What to do

General, cautious steps (verify details in the official source):

• Review exposure and plan remediation based on risk and environment.
• Identify affected product versions in your inventory and verify whether you are impacted.
• Apply vendor patches/updates or recommended mitigations as soon as available.
• Read the official advisory for exact affected versions and remediation steps.

Official advisory

• Read the official source
• CVE Record
• NVD

Evidence and provenance

Canonical advisory ID

GHSA-W2QP-RPH6-63G4

Source

GitHub

Vendor

GitHub

Published by source

2026-09-02

Last source activity

2026-09-02

Additional identifiers

CVE-2026-18504

Curated by

hlukh.ch

Related advisories and connections

These advisories are connected by shared CVE, product, vendor, source, or time signals.