Is this a bug report?

Yes

Did you try recovering your dependencies?

Not relevant.

Which terms did you search for in User Guide?

(Write your answer here if relevant.)

Environment

1. node -v: v9.7.1
2. npm -v: v5.6.0
3. yarn --version (if you use Yarn):
4. npm ls react-scripts (if you haven’t ejected):

Then, specify:

1. Operating system:
   MacOSX Sierra 10.12.6
   MacOSX Sierra 10.13.3
2. Browser and version (if relevant):

Steps to Reproduce

(Write your steps here:)

1. npm run start # fresh installation

Expected Behavior

If it's an error caused by the system configuration, it probably should suggest something meaningful.

Actual Behavior

This issue has been reported on a bunch of different repositories:
halfzebra/create-elm-app#239
node-modules/detect-port#29

The original maintainer @fengmk2 says it has been fixed in the original detect-port package.

Reproducible Demo

Not available.