The 5th Annual China PHP Conference

Voting

Please answer this simple SPAM challenge: max(nine, zero)?
(Example: nine)

The Note You're Voting On

ceo at l-i-e dot com
12 years ago
Using /var/www/uploads in the example code is just criminal, imnsho.

One should *NOT* upload untrusted files into your web tree, on any server.

Nor should any directory within your web tree have permissions sufficient for an upload to succeed, on a shared server. Any other user on that shared server could write a PHP script to dump anything they want in there!

The $_FILES['userfile']['type'] is essentially USELESS.
A. Browsers aren't consistent in their mime-types, so you'll never catch all the possible combinations of types for any given file format.
B. It can be forged, so it's crappy security anyway.

One's code should INSPECT the actual file to see if it looks kosher.

For example, images can quickly and easily be run through imagegetsize and you at least know the first N bytes LOOK like an image.  That doesn't guarantee it's a valid image, but it makes it much less likely to be a workable security breaching file.

For Un*x based servers, one could use exec and 'file' command to see if the Operating System thinks the internal contents seem consistent with the data type you expect.

I've had trouble in the past with reading the '/tmp' file in a file upload.  It would be nice if PHP let me read that file BEFORE I tried to move_uploaded_file on it, but PHP won't, presumably under the assumption that I'd be doing something dangerous to read an untrusted file.  Fine.   One should move the uploaded file to some staging directory.  Then you check out its contents as thoroughly as you can.  THEN, if it seems kosher, move it into a directory outside your web tree.  Any access to that file should be through a PHP script which reads the file.  Putting it into your web tree, even with all the checks you can think of, is just too dangerous, imnsho.

There are more than a few User Contributed notes here with naive (bad) advice.  Be wary.

<< Back to user notes page

To Top