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.
Advisories
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Fixes
Solution
No solution given by the vendor.
Workaround
No workaround given by the vendor.
References
History
Fri, 04 Sep 2026 12:15:00 +0000
| Type | Values Removed | Values Added |
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| Weaknesses | CWE-179 | |
| References |
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| Metrics |
threat_severity
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threat_severity
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Fri, 04 Sep 2026 10:45:00 +0000
| Type | Values Removed | Values Added |
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| First Time appeared |
Fastify
Fastify fastify |
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| Vendors & Products |
Fastify
Fastify fastify |
Fri, 04 Sep 2026 09:45:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| 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. | |
| Title | fastify vulnerable to request body replacement via an async validation result collision | |
| Weaknesses | CWE-20 | |
| References |
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| Metrics |
cvssV3_1
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Projects
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Status: PUBLISHED
Assigner: openjs
Published:
Updated: 2026-09-04T09:40:18.120Z
Reserved: 2026-09-01T21:10:05.765Z
Link: CVE-2026-84504
No data.
Status : Received
Published: 2026-09-04T10:17:13.790
Modified: 2026-09-04T10:17:13.790
Link: CVE-2026-84504
OpenCVE Enrichment
Updated: 2026-09-04T13:30:05Z