Vulnerability · Published Aug 6, 2026 · Assigned by openjs
CVE-2026-18427@fastify/static vulnerable to route guard bypass via non-canonical path segments
High 7.5
In plain English
A high-severity path traversal in @fastify/static from @fastify/static. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.7% (higher than 52% of all known vulnerabilities).
Official description
@fastify/static before version 10.1.3 contains an incomplete fix for a previous route guard bypass. The static file handler rejected only parent directory segments, but it did not canonicalize dot segments, duplicate slashes, encoded dots, or backslashes before route matching and before delegating to the send layer. As a result, an unauthenticated attacker could request a file protected by a route based guard using a non canonical path form that misses the guarded route yet resolves back onto the protected file, disclosing its contents. Applications that protect a subtree of the static root with a route based guard are affected, while applications relying on the allowedPath option are not. This is fixed in @fastify/static 10.1.3, which canonicalizes the pathname, including rejecting backslashes, on the path used for routing and serving.
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| @fastify/static | @fastify/static | 0 – before 10.1.3 |
Weakness: CWE-22, CWE-436 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N