I am writing a script that will allow teachers to upload files (called activity sheets) via a Web form. The files are then subsequently written out to a directory on the server which has Web access forbidden to everyone via an .htaccess file. Even I, who have root access, cannot access the file through a browser. The file cannot be viewed by the general public until I have manually examined it and determined that it is exactly what it is supposed to be (word processing documents, images, and spreadsheets. Nothing else is allowed) and has no macrovirii. I think this part is relatively secure.

My humble supplication for information from wiser monks is this: what type of security holes exist with a browse button? The relevant Perl code: 

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.
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use CGI;
my $template = new CGI;
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sub storeSheet {
    my ($sheet, $file, $data) = @_;
        my ($path, $filename);
    my $storagePath = "/www/htdocs/documents/activity_sheets/";
    
    # Here we extract the filename and file

    $path = $template->param($sheet);
    $path =~ m!([^/:\\]*)$!; # capture filename
    $filename = $1;

    no strict 'refs'; # $filename is a symbolic reference
    open (SHEET, ">${storagePath}OSEN${filename}") || die "Can't open 
+$filename: $!\n";
    while (read($path, $data, 1024)) {
        print SHEET $data;    
    }
    close SHEET;
    use strict 'refs';
}

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I had a devil of a time just finding information about how to do this. I have two concerns.
  1. What dangers are involved in my using "no strict 'refs';" here and how can I avoid this?
  2. Users can supply their own path information. I'm not sure how security works here. Can they include a path with backticks and execute their own code? Is there anything else I need to know about this>
Any wisdom on this matter would be greatly appreciated. If their are other concerns, I would love to know about them.

Incidentally, I've reduced this to a minimal test case, so my apologies if I missed anything in the code.

Cheers!

In reply to File Upload Security Question by Ovid

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