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CVE-2026-84469— fastify vulnerable to request validation bypass via skipped boolean false schemas

Quick assessment

Affected
fastify fastify
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

在 fastify 5.12.2 版本之前，该库通过 JavaScript 的“真值”（truthiness）判断来决定是否编译请求模式（request schema）。然而，JSON Schema Draft 7 明确定义布尔值 是一个有效的模式，其作用是拒绝所有实例。 当应用程序将路由的 body、querystring、params 或 headers 的模式（schema）设置为 以拒绝所有输入时，fastify 会将其视为“缺少模式”，从而不编译任何校验器（validator），导致路由处理函数（rout

CVSS 7.5 · High EPSS 0.52% · P42

Affected Version Matrix 2

VendorProduct Version RangeStatus
fastify fastify < 5.12.2 affected
5.12.2 unaffected
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I. Basic Information for CVE-2026-84469

Vulnerability Information
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Vulnerability Title
fastify vulnerable to request validation bypass via skipped boolean false schemas
Source: CVE Program / CVE List V5
Vulnerability Description
fastify versions before 5.12.2 decide whether to compile a request schema based on JavaScript truthiness, but JSON Schema Draft 7 defines the boolean false as a valid schema that rejects every instance. When an application assigns false to a route's body, querystring, params, or headers schema to deny all input, fastify treats it as a missing schema, compiles no validator, and runs the route handler on any request. An unauthenticated remote client can therefore reach a handler that a valid deny-all schema was intended to make unreachable, a complete validation bypass that can lead to unauthorized state changes or execution of disabled operations. Users should upgrade to fastify 5.12.2 or later.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
输入验证不恰当
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
fastify fastify 0 ~ 5.12.2 -

II. Public POCs for CVE-2026-84469

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III. Intelligence Information for CVE-2026-84469

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Vendor Advisories for CVE-2026-84469 (1)

Same Patch Batch · fastify · 2026-09-04 · 4 CVEs total

CVE-2026-84504 8.1 HIGH fastify vulnerable to request body replacement via an async validation result collision
CVE-2026-76169 7.5 HIGH fastify vulnerable to authentication bypass via malformed URLs reaching encapsulated not-f
CVE-2026-84428 7.5 HIGH fastify vulnerable to header validation bypass via incomplete schema case normalization

IV. Related Vulnerabilities

Same product: fastify
Same vendor: fastify
Same weakness: CWE-20

V. Comments for CVE-2026-84469

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