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CVE-2026-84469

7.5 · HIGH

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 inst…

Published Sep 4, 2026fastifyCWE-20EPSS 0.49%

Overview

CVE-2026-84469 is a high-severity vulnerability affecting fastify fastify. It was published on September 4, 2026 and has a CVSS 3.1 base score of 7.5 (HIGH).

This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

Technical 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.

Remediation

Check the references section for vendor advisories and patches from fastify. Update fastify to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

Affected products

VendorProductVersionsStatus
fastifyfastify>= 0, < 5.12.2Affected

References

Refcna.openjsf.org/security-advisories.htmlGitHubgithub.com/fastify/fastify/security/advisories/GHSA-hwr6-493r-vm6h

How CyberStrike helps

Frequently asked questions

What is CVE-2026-84469?

CVE-2026-84469 is a high-severity vulnerability affecting fastify fastify. It was published on September 4, 2026 and has a CVSS 3.1 base score of 7.5 (HIGH).

How severe is CVE-2026-84469?

This vulnerability has a CVSS 3.1 base score of 7.5, rated HIGH. It can be exploited remotely over the network. No authentication or special privileges are required for exploitation.

How do I fix or remediate CVE-2026-84469?

Check the references section for vendor advisories and patches from fastify. Update fastify to the latest patched version. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

How can CyberStrike help with CVE-2026-84469?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-84469 is actually reachable in your own applications and APIs, then verifies each finding before reporting it. That tells you if the weakness is a real, exploitable risk in your environment or a false positive you can safely deprioritize.

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