CVE-2026-33806

Summary

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 Software

Weaknesses

• CWE-1287: CWE-1287: Improper Validation of Specified Type of Input

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: none
  • Automatable: yes
  • Technical Impact: partial

fastify: Fastify: Schema validation bypass via malformed Content-Type header

Additional References

• 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

References

• https://github.com/fastify/fastify/security/advisories/GHSA-mg2h-6x62-wpwc
• https://cna.openjsf.org/security-advisories.html

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