Exploited  mailer - how to fix  script

Posted on 2006-07-19
Last Modified: 2013-12-25
I have been thrown into fixing a problem I am not sure I know where to start.

A spammer has been using the cgi-bin/mailer.cgi script to sent spam through my hosting server.  The host has disabled the script, but we would like to reenable it.  

I understand that I need to modify the script to check *all* form variables which are used to generate the email headers and ensure that they do not contain any newline or carriage return characters.

Having said that, I am not a programmer and am not sure how to modify the code.

This is the code in question:


use CGI::Carp qw(fatalsToBrowser);
require '';
$in{'comments'} =~ s/\015\012/ /g;

# enter who the mail goes to below;

# URL for the page to be displayed after form submission;

# Path to your mail prog;
$mailprog = '/usr/sbin/sendmail';

# The subject of your mail (In the HIDDEN tag);
$subject="AM Comments";

open(MAIL,"|$mailprog -t");
print MAIL "To: $recip\n";
print MAIL "From: $in{'email'} ($in{'fname'} $in{'lname'})\n";
print MAIL "Subject: $subject\n";
print MAIL<<EOF;
This mail came from the your AM website's contact page:

Name:                        $in{'name'}
E-mail:                   $in{'email'}
Message:                  $in{'message'}

close MAIL;
open (MAILOG,">>maillog_contact.txt");
print MAILOG "$today|$in{name}|$in{email}|$in{message}|$in{field2}|$in{field3}|\n";
close MAILOG;
print "Location: $redirect\n\n";
sub Get_Date {
      @days =
      @months =
      $time = time;
      ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday,$isdst) =
      $year = 1900+$year;
      $mon=$mon + 1;
      $todaydate = "$year/$mon/$mday ";
      $todaydate = $todaydate."$hour\:$min\:$sec";

Question by:franco2
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LVL 51

Expert Comment

ID: 17157265
> ensure that they do not contain any newline or carriage return characters.
you better use a whitelist instead of a blacklist to sanatize input, something like:

  $in{'email'} =~ s/[^a-zA-Z0-9\.\@-]//g;

i.g. I'd never sanatize input, but reject it and abort the complete request if does not match my whitelist

Author Comment

ID: 17157509
Great info - not sure what a whitelist or blacklist are. Would the script look like this?

This mail came from the your AM website's contact page:

Name:                    $in{'name'}
E-mail:                 $in{'email'} =~ s/[^a-zA-Z0-9\.\@-]//g
Message:               $in{'message'}


Also, does the script need to compile once the problem is fixed. If yes - I do not have perl - how do I make the bin workable.

Again, pardon my ignorance - I am not a programmer.

Thanks in advance.
LVL 51

Accepted Solution

ahoffmann earned 350 total points
ID: 17157645
> not sure what a whitelist or blacklist are.
with a blacklist you allow anything not listed (your aproach), with a whitelist you allow anything listed (in particular that which your defined harmless:).

> Also, does the script need to compile once the problem is fixed.
no, perl is a interpreter
Only if you have fastCGI  or something similar in use, then you need to restart your server.

> Would the script look like this?
not as you did it, more like (a snippet only):

 $in{'fname'}=~ s/[^a-zA-Z'-]//g;
 $in{'lname'}=~ s/[^a-zA-Z'-]//g;
 $in{'email'} =~ s/[^a-zA-Z0-9\.\@-]//g;

Name:                    $in{'name'}
E-mail:                 $in{'email'}
Message:               $in{'message'}

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