What’s Vulnerable › Vulnerabilities

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

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.4% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-04-15 · updated 2026-07-15
• Weakness: CWE-1287

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 products

• fastify: from 5.3.2 before 5.8.5 — fixed in 5.8.5

How to fix

Upgrade to a fixed version: fastify 5.8.5. Check the vendor advisory for mitigations.

References

• https://cna.openjsf.org/security-advisories.html
• https://github.com/fastify/fastify/security/advisories/GHSA-mg2h-6x62-wpwc
• https://access.redhat.com/security/cve/CVE-2026-33806
• https://bugzilla.redhat.com/show_bug.cgi?id=2458596
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-33806.json

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