CVE-2026-76169 - fastify vulnerable to authentication bypass via malformed URLs reaching encapsulated not-found handlers
CVE ID :CVE-2026-76169
Published : Sept. 4, 2026, 10:17 a.m. | 47 minutes ago
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.
Severity: 7.5 | HIGH
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Published : Sept. 4, 2026, 10:17 a.m. | 47 minutes ago
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.
Severity: 7.5 | HIGH
Visit the link for more details, such as CVSS details, affected products, timeline, and more...