serve-static prior to 1.6.5 ( or 1.7.x prior to 1.7.2 ) are affected by an open redirect vulnerability on some browsers when configured to mount at the root directory.
Proof of Concept
A link to
http://example.com//www.google.com/%2e%2e will redirect to
Some browsers will interpret this as
http://www.google.com/%2e%2e, resulting in an external redirect.
Version 1.7.x: Update to version 1.7.2 or later. Version 1.6.x: Update to version 1.6.5 or later.