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HIGH

CVE-2026-84504

CVSS v3

8.1

HIGH

EPSS Score

0.4 %

exploit probability, as of 2026-09-28

CISA KEV

No

known exploited

Exploitation

—

SSVC status

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

Technical details

Published
2026-09-04
Last Modified
2026-09-04

Frequently asked questions

What is CVE-2026-84504?

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

Is CVE-2026-84504 actively exploited?

Active exploitation of CVE-2026-84504 has not been confirmed. Its EPSS score was 0.4% on 2026-09-28, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-84504?

CVE-2026-84504 has a CVSS v3 base score of 8.1 (HIGH severity).

Is CVE-2026-84504 affecting your environment?

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