Re: File Upload Security

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Al wrote:
Thanks guys.

I had written a newer version restricted to images which checks MIME and image width and height.

I have one application which needs a text file. I think I'll have my users hide a password in it and scan the whole file for <? an <?php and other signs of scripts, etc.

Al wrote:
One of my sites has been hacked and I'm trying to find the hole. The hack code creates dirs with "nobody" ownership, so it's obvious stuff is not via ftp [ownership would be foo]

Site is virtual host, Linux/Apache

I'm concerned about a file uploader my users use to upload photos.

Can anyone see a hole in this scrip? Can my code upload an executable masquerading as an image file?

You probably need a deeper inspection than checking the extension - that's Microsoft thinking... You can't trust what the client is telling you - even the MIME type sent by the browser is no guarantee. Since you're on Linux, why not look at using the 'file' shell command to get a more detailed inspection of the upload. I made a basic function like this a few years ago - probably needs a bit of tweaking:

<?php
    function getMimeType($file)
    {
	global $magicFile;
$mimecmd = "/usr/bin/file -b -m ".escapeshellargs($magicFile)." ".escapeshellargs($file)." 2> /dev/null";
        $ret = exec($mimecmd);
        if (!$ret)
        {
            $ret = "unknown";
        }
        return $ret;
    }
?>

The global $magicFile is the tricky bit - you need to find a nice Unix magic numbers file that returns mime types (they're easier to parse than regular magic number responses). Probably something like /usr/share/misc/magic.mime, but that depends on the system.


--
Peter Ford                              phone: 01580 893333
Developer                               fax:   01580 893399
Justcroft International Ltd., Staplehurst, Kent

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