Input validation error in Fastify - CVE-2026-84469
Published: September 7, 2026
Vulnerability identifier: #VU147203
CSH Severity: Medium
CVSS v4: 8.7 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-84469
CWE-ID: CWE-20
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to bypass request validation.
The vulnerability exists due to improper input validation in Fastify request-part schema validation when handling requests whose body, query string, parameters, or headers are configured with a boolean false schema. A remote attacker can send a request containing arbitrary input to bypass request validation.
The documented query alias for query string schemas is also affected.
Affected software
Fastify
How to mitigate CVE-2026-84469
Install security update from vendor's website.
Fastify - update to 5.12.2