You know what? Rather than over-complicate things you can probably just check that filenames only contain a small set of white-listed chars. [a-zA-z-._] (and != ‘…’ or ‘.’) or something.

And one other nit-pick if you’re up for more code-review - your authentication logic should probably be inverted:

if !ok || user != session.config.username ||
				pass != session.config.password

I’d change that to be something like

if ok && user == session.config.username && pass == session.config.password {
   // do login
} else {
   // not auth
}

There’s a whole category of security errors where an exception in logic like that causes the code to skip the “you’re not allowed” logic and go right to the “you’re allowed!” block. It’s more of an issue with languages that support exceptions but it’s still considered a best practice generally (it’s also typically easier to read).

At the time I made the comment, I didn’t realize this was building with unsanitized inputs and absolute paths.

And I should know better, I use burp a couple times a month. My bad.