CVE-2026-33806
fastify vulnerable to Body Schema Validation Bypass via Leading Space in Content-Type Header
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.
INFO
Published Date :
April 15, 2026, 4:17 a.m.
Last Modified :
April 17, 2026, 3:49 p.m.
Remotely Exploit :
No
Source :
ce714d77-add3-4f53-aff5-83d477b104bb
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 3.1 | HIGH | ce714d77-add3-4f53-aff5-83d477b104bb | ||||
| CVSS 3.1 | HIGH | MITRE-CVE |
Solution
- Upgrade to Fastify v5.8.5 or later.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-33806.
| URL | Resource |
|---|---|
| https://cna.openjsf.org/security-advisories.html | Vendor Advisory |
| https://github.com/fastify/fastify/security/advisories/GHSA-mg2h-6x62-wpwc | Not Applicable |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-33806 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-33806
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-33806 vulnerability anywhere in the article.
-
Daily CyberSecurity
Active SharePoint Spoofing and Legacy Office RCE: CISA Alerts on New KEV Exploits
The Cybersecurity and Infrastructure Security Agency (CISA) has expanded its Known Exploited Vulnerabilities (KEV) Catalog, sounding a fresh warning about two high-risk security flaws currently being ... Read more
-
Daily CyberSecurity
25 Million Users at Risk: Fastify Publicly Discloses PoC Exploit for Single-Space Security Bypass
In the world of web performance, Fastify is a heavyweight, boasting over 25 million monthly downloads and a reputation for being one of the fastest frameworks available. However, a newly disclosed vul ... Read more
The following table lists the changes that have been made to the
CVE-2026-33806 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
Initial Analysis by [email protected]
Apr. 17, 2026
Action Type Old Value New Value Added CPE Configuration OR *cpe:2.3:a:fastify:fastify:*:*:*:*:*:node.js:*:* versions from (including) 5.3.2 up to (excluding) 5.8.5 Added Reference Type openjs: https://cna.openjsf.org/security-advisories.html Types: Vendor Advisory Added Reference Type openjs: https://github.com/fastify/fastify/security/advisories/GHSA-mg2h-6x62-wpwc Types: Not Applicable -
New CVE Received by ce714d77-add3-4f53-aff5-83d477b104bb
Apr. 15, 2026
Action Type Old Value New Value Added 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. Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N Added CWE CWE-1287 Added Reference https://cna.openjsf.org/security-advisories.html Added Reference https://github.com/fastify/fastify/security/advisories/GHSA-mg2h-6x62-wpwc