OSEC

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From: b0iler (b0ilereyeonsecurity.net)
Date: Sat Jun 22 2002 - 00:59:35 CDT

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    Taken from the scripts website:
    "WARNING: DPGS is no longer maintained and is thus discontinued. If you would like to take over its development, email me. - July 30, 2000"

    This is the reasoning to why I did not contact the author prior to this email.

    This is an example of how bad input filtering and open() based on user input make a nasty combo.

    the script is Duma Photo Gallery System and in update.dpgs lies the problem open():

    open(DATABASE, ">$path_to_members/$FORM{'id'}/data.txt")
            || &error("Couldn't write $path_to_members/$FORM{'id'}/data.txt");
            
    while ( ($form_key, $form_value) = each(%FORM) ) {
            print DATABASE "$form_key$delimiter$form_value\n" unless
                    ( $form_value eq '' || $form_key eq "id" || $form_key =~ "password" );
    }
    close(DATABASE);

    this will open the database of this user and then try to add data to the database. Now
    here is what %FORM is filtered by in DPGS.pll:

            $value =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C", hex($1))/eg;
            $value =~ s/<([^>]|\n)*>//g;
            $value =~ s/<!--(.|\n)*-->//g; #removes any server side includes
            $value =~ s/^\s+//; #remove any leading spaces
            $value =~ s/\s+$//; #remove any trailing spaces
            $value =~ s/$delimiter//g; #remove delimiters if any.
            $value =~ s/\"/\&quot\;/g; #replace quotes with &quot;
            $value =~ s/\r\n/<BR>/g; #replace new line characters with <BR>
            $FORM{$name} = $value;
            }
            
    none of these stop directory transversal or the null byte. So if we sign up with an id of ../../etc/passwd\0 then the /etc/passwd file will be the one opened for writting. We can write to any file this way, even overwritting other user's data.txt files or
    the admin data file '../admin'.

    No fix is on hand, but feel free to come up with your own. Filter for null bytes and reverse directory
    transversal.

    b0iler - http://b0iler.eyeonsecurity.net

    make sure to check out http://b0iler.eyeonsecurity.net/tutorials/hackingcgi.htm for a great paper on perl cgi security and exploitation. Many new methods of exploiting common perl cgi code. Including the s/<!--(.|\n)*-->//g; "filter" which is used in this script and thousands of others.