To safely create a temporary file in the OS temp dir in a multi-user environment you must:

• Ensure that the file is created with 0o600 permissions or similar.
• Ensure that you're not reusing an existing file (Use the O_EXCL and O_CREAT flags)
  (An exploit requires extremely precise timing by inserting a file between an fs.exists(..) and a fs.open(..) call.)

This query checks for the first of these requirements.

The only way to ensure the second requirement is to use fs.open(.., O_EXCL | O_CREAT), which is what e.g. tmp does.
Checking for the second requirement gets complicated. One of the complications is that NodeJS programs very rarely use file handles, and instead just calls the fs module multiple times with the same string path.
So I went the easy route and just look for bad permissions, which is the most important part.
(But the recommendation in the .qhelp basically says: use tmp. Because that package does everything right).

I haven't found any FPs.
But I suspect that FPs might happen when a program safely creates a temp file in a utility method, but the query still sees that utility method as a source.

An evaluation shows no new results, and a constant 30s slowdown (that's the extra time it takes to compile the query, something went wrong in a preparation step).
So the evaluation show no noticeable slowdown.

A test run finds some results.
All the results are either in test code or benign, which is why I've set the precision to medium.