CVE-2026-76169
Dashboard / Vulnerabilities / CVE-2026-76169
Summary: fastify vulnerable to authentication bypass via malformed URLs reaching encapsulated not-found handlers
Details: 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.
References: https://cna.openjsf.org/security-advisories.html, https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/76xxx/CVE-2026-76169.json, https://github.com/fastify/fastify/security/advisories/GHSA-p68q-wchp-6fh7, https://nvd.nist.gov/vuln/detail/CVE-2026-76169
Affected packages
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Affected ranges
Type: GIT
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