Search/CVE-2026-18504
CVE — Medium

CVE-2026-18504

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 v3.1
5.4 MEDIUM
EPSS
0.31%
probability of exploitation in 30 days
CISA KEV
Not listed
no confirmed exploitation reported
News coverage
0
sources referencing this CVE
EPSS Trend
Aug 20, 2026Sep 4, 2026
0.00pp
0.31% → 0.31% over 2 tracked changes
CVSS v3.1 Detail
Attack VectorNETWORK
Attack ComplexityLOW
Privileges RequiredLOW
User InteractionNONE
ScopeUNCHANGED
ConfidentialityLOW
IntegrityLOW
AvailabilityNONE
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
Connections
2 relationships
Timeline
disclosure → media coverage
Aug 18, 2026
Disclosure — published as a CVE record. · last revised by NVD Sep 2, 2026
Public PoC (1)
Unverified third-party code — review before executing.