@fastify/static versions 8.0.0 through 9.1.0 allow path traversal when directory listing is enabled via the list option. The dirList.path() function resolves directories outside the configured static root using path.join() without a containment check. A remote unauthenticated attacker can obtain directory listings for arbitrary directories accessible to the Node.js process, disclosing directory and file names.

File contents are not disclosed. Upgrade to @fastify/static 9.1.1 to fix this issue. As a workaround, disable directory listing by removing the list option from the plugin configuration.