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CVE-2026-76169

7.5 · HIGH

fastify versions >= 4.0.0 and before 5.12.2 can route a malformed URL sent under one plugin prefix to the custom not-found handler of a different sibling plugin, and invoke it without the preHandle…

Published Sep 4, 2026fastifyCWE-288EPSS 0.53%

Overview

CVE-2026-76169 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 >= 4.0.0 and before 5.12.2 can route a malformed URL sent under one plugin prefix to the custom not-found handler of a different sibling plugin, and invoke it without the preHandler hook declared for that handler. The internal not-found router for encapsulated handlers dispatches malformed paths through a single shared handler pointer before URL decoding, ignoring the prefix and skipping the selected handler's normal lifecycle. An unauthenticated attacker can therefore reach an authentication-protected private fallback through an unrelated public prefix and read its full response, bypassing the authentication hook and breaking prefix encapsulation. 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>= 4.0.0, < 5.12.2Affected

References

Refcna.openjsf.org/security-advisories.htmlGitHubgithub.com/fastify/fastify/security/advisories/GHSA-p68q-wchp-6fh7

How CyberStrike helps

Frequently asked questions

What is CVE-2026-76169?

CVE-2026-76169 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-2026-76169?

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-2026-76169?

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-2026-76169?

CyberStrike is an open-source, AI-augmented pentesting engine. Rather than flag a version number, it tests whether an issue like CVE-2026-76169 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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