fastify vulnerable to Body Schema Validation Bypass via Leading Space in Content-Type Header
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- —
- Confidentiality · integrity · availability
- None · High · None
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub.
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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- Yes
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| fastify | fastify | 5.3.2 to before 5.8.5 | 5.8.5 | Patch available | CNA |
| — | fastify (npm) | 5.3.2 to before 5.8.5 | 5.8.5 | Patch available | GHSA-247c-9743-5963 |
- fastify Vendorfastify Affected 5.3.2 to before 5.8.5 Fixed in 5.8.5 Patch available CNA
- fastify (npm) Vendor— Affected 5.3.2 to before 5.8.5 Fixed in 5.8.5 Patch available GHSA-247c-9743-5963
Remediation
- Fix · CNA fastify (fastify) Fixed in 5.8.5
- Fix · GHSA-247c-9743-5963 fastify (npm) Fixed in 5.8.5 Advisory →
Vendor assessments
Red Hat
Red Hat rating: Important. Red Hat's page for this CVE →
Not affected: 3 products
- Red Hat Enterprise Linux AI (RHEL AI) 3
- Red Hat OpenShift AI (RHOAI)
- Red Hat OpenShift Dev Spaces
Timeline
- 2026-10-02 Threatist record created from CVE-2026-33806
- 2026-10-03 Alias added: GHSA-247c-9743-5963
References
Advisory 3
Other 5
- https://github.com/fastify/fastify/security/advisories/GHSA-mg2h-6x62-wpwc
- https://github.com/fastify/fastify/security/advisories/GHSA-247c-9743-5963
- https://github.com/fastify/fastify/commit/f3d2bcb3963cd570a582e5d39aab01a9ae692fe4
- https://github.com/fastify/fastify
- https://github.com/fastify/fastify/releases/tag/v5.8.5
More Fastify vulnerabilities
- TI-2022-18664 Denial of service in Fastify via Content-Type header CVSS 3.1HIGH 7.5
- TI-2025-23513 Fastify vulnerable to invalid content-type parsing, which could lead to validation bypass CVSS 3.1HIGH 7.5
- TI-2026-58050 fastify vulnerable to request validation bypass via skipped boolean false schemas CVSS 3.1HIGH 7.5
- TI-2026-58022 fastify vulnerable to header validation bypass via incomplete schema case normalization CVSS 3.1HIGH 7.5
- TI-2026-53284 fastify vulnerable to authentication bypass via malformed URLs reaching encapsulated not-found handlers CVSS 3.1HIGH 7.5
- TI-2026-58072 fastify vulnerable to request body replacement via an async validation result collision CVSS 3.1HIGH 8.1
Sources
- CVE-2026-33806 · CVE Program
- CVE-2026-33806 · NVD
- FIRST EPSS
- GHSA-247c-9743-5963 · GitHub Advisory Database · CC BY 4.0
- CVE-2026-33806 · Red Hat security data · CC BY 4.0
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