Improper Validation of Specified Type of Input in Fastify - CVE-2026-33806
Published: April 14, 2026
Vulnerability identifier: #VU125980
CSH Severity: Medium
CVSS v4.0: 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/E:U/U:Green
CVE-ID: CVE-2026-33806
CWE-ID: CWE-1287
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: fastify.io
Affected software:
Fastify
Fastify
Detailed vulnerability description
The vulnerability allows a remote attacker to bypass body schema validation.
The vulnerability exists due to improper validation of specified type of input in schema.body.content validation in lib/validation.js when processing requests with a Content-Type header prefixed by a leading space. A remote attacker can send a specially crafted request to bypass body schema validation.
The issue is caused by a parser-validator differential where the body is still parsed correctly after leading whitespace is trimmed, but validator lookup uses an empty media type and skips validation.
How to mitigate CVE-2026-33806
Install security update from vendor's website.