Vulnerability Description
fastify versions before 5.12.2 treat the object resolved by a successful Ajv async validator as the value result protocol used by custom validator compilers. If a request that passes its route schema contains a property named value at the root, fastify replaces the entire request body with that property's value before the handler runs, so the handler receives a different object than the one that satisfied the schema. An authenticated low-privilege caller can use this to make nested data replace the validated body and trigger an operation the route schema did not authorize, leading to unauthorized state changes and data disclosure. Users should upgrade to fastify 5.12.2 or later.
CVSS Score
HIGH
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Fastify | Fastify | < 5.12.2 |
Related Weaknesses (CWE)
References
- https://cna.openjsf.org/security-advisories.htmlThird Party Advisory
- https://github.com/fastify/fastify/security/advisories/GHSA-667r-xxjv-c9mmMitigationVendor Advisory
FAQ
What is CVE-2026-84504?
CVE-2026-84504 is a vulnerability with a CVSS score of 8.1 (HIGH). fastify versions before 5.12.2 treat the object resolved by a successful Ajv async validator as the value result protocol used by custom validator compilers. If a request that passes its route schema ...
How severe is CVE-2026-84504?
CVE-2026-84504 has been rated HIGH with a CVSS base score of 8.1/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-84504?
Check the references section above for vendor advisories and patch information. Affected products include: Fastify Fastify.