@hapi/inert has a static-file confinement bypass via sibling-prefix path

Impact

@hapi/inert serves static files from a directory configured with path (in the directory / file handlers) or relativeTo (for h.file()), with confinement enforced by the confine option (default true). Before the patch, the confinement check compared the resolved absolute path against the confine directory using a raw string-prefix test, so a sibling directory whose absolute path begins with the same characters as the confine directory (eg. /app/static-secret next to a served /app/static) was incorrectly accepted as confined. An unauthenticated remote attacker who knows or guesses such a sibling name can read any file inside it via a request like /..%2fstatic-secret/secret.txt, provided the file is readable by the server process. Only applications that happen to have a sibling directory sharing a string prefix with the served directory are exploitable; applications with no such sibling are unaffected.

Patches

Upgrade to 7.1.1.

Workarounds

For users who cannot upgrade immediately: ensure the directory served via inert has no sibling whose name starts with the same characters (for example, rename static-secret/ to secret/, or move it to a different parent directory).

Resources

Pull Request: https://github.com/hapijs/inert/pull/176