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.
Metrics
Affected Vendors & Products
References
History
Fri, 04 Sep 2026 17:30:00 +0000
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ssvc
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Fri, 04 Sep 2026 12:15:00 +0000
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| Weaknesses | CWE-179 | |
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threat_severity
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threat_severity
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Fri, 04 Sep 2026 10:45:00 +0000
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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 |
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| 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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Status: PUBLISHED
Assigner: openjs
Published: 2026-09-04T09:40:18.120Z
Updated: 2026-09-04T16:34:58.664Z
Reserved: 2026-09-01T21:10:05.765Z
Link: CVE-2026-84504
Updated: 2026-09-04T16:34:53.741Z
Status : Awaiting Analysis
Published: 2026-09-04T10:17:13.790
Modified: 2026-09-08T19:07:52.113
Link: CVE-2026-84504