CVE-2026-14198 @fastify/middie vulnerable to authorization bypass via encoded slash in path parameter values
Attackers can bypass authentication or authorization checks in @fastify/middie by using encoded slashes in path parameters, allowing unauthorized access to protected handlers.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-14198?
CVE-2026-14198 is a critical authentication bypass vulnerability in @fastify/middie, published on 1 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
@fastify/middie versions 9.1.0 through 9.3.2 decode the encoded slash %2F inside path parameter values before matching middleware paths, while Fastify's underlying router preserves the encoding during route lookup. The two layers disagree on the canonical request path, so the middleware fails to match a URL that the route handler does match. When middleware is used for authentication, authorization, rate limiting, or auditing on parameterized paths, an attacker can reach the protected handler by sending a single crafted URL with an encoded slash in the parameter position. The bypass is HTTP method agnostic and requires no authentication or special preconditions. Patches: upgrade to @fastify/middie 9.3.3. Workarounds: avoid parameterized middleware paths for security decisions, or enforce authentication at the route handler or via a Fastify hook that runs after the router has resolved the request.
Weakness: CWE-436
Which versions are affected by CVE-2026-14198?
It affects 1 product.
Products include Fastify Fastify\/Middie.
How do I fix CVE-2026-14198?
No fix has been published for CVE-2026-14198 yet. Limit exposure of the affected software until one is available.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-14198 being exploited?
There is no known exploitation of CVE-2026-14198 in the wild and no public exploit code.
Other vulnerabilities in @fastify/middie
- CVE-2026-85184 @fastify/middie vulnerable to path-scoped middleware bypass via absolute-form request target
- CVE-2026-6270 @fastify/middie vulnerable to middleware authentication bypass in child plugin scopes
- CVE-2026-22031 Fastify Middie Middleware Path Bypass
- CVE-2026-2880 @fastify/middie has an improper path normalization vulnerability
- CVE-2026-14181 @fastify/middie standalone engine vulnerable to Denial of Service via malformed percent-encoded paths
Sources
Also known as GHSA-2v46-jxjm-7q3v.