Vulnerability · Published Apr 15, 2026 · Assigned by openjs

CVE-2026-33806fastify vulnerable to Body Schema Validation Bypass via Leading Space in Content-Type Header

High 7.5

In plain English

A high-severity security flaw in fastify from fastify. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 39% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.5High

Exploit odds (30 days)0.4%top 60.9% of all CVEs

Exploited in the wildNo reportsCISA SSVC: none

Attack toolingNoneno public tooling known

Official description

Impact: Fastify applications using schema.body.content for per-content-type body validation can have validation bypassed entirely by prepending a space to the Content-Type header. The body is still parsed correctly but schema validation is skipped. This is a regression introduced in fastify >= 5.3.2 by the fix for CVE-2025-32442 Patches: Upgrade to fastify v5.8.5 or later. Workarounds: None. Upgrade to the patched version.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
npm	fastify	5.8.5	GHSA-247c-9743-5963
npm	fastify	5.3.2	GHSA-mg2h-6x62-wpwc
npm	fastify	4.29.1	GHSA-mg2h-6x62-wpwc

Affected products (as reported)

Vendor	Product	Versions
fastify	fastify	5.3.2 – before 5.8.5

Weakness: CWE-1287, CWE-1289 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

References

https://github.com/fastify/fastify/security/advisories/GHSA-mg2h-6x62-wpwc
https://cna.openjsf.org/security-advisories.html
https://access.redhat.com/security/cve/CVE-2026-33806 vdb-entry, x_refsource_REDHAT
RHBZ#2458596 issue-tracking, x_refsource_REDHAT
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33806.json x_sadp-csaf-vex