Stopping Spambots: A Spambot Trap

Neil Gunton writes "Having been hit by a load of spambots on my community site, I decided to write a Spambot Trap which uses Linux, Apache, mod_perl, MySQL, ipchains and Embperl to quickly block spambots that fall into the trap. "

Elements of good design I'd missed

Looking at my Day Job and personal web site, other than the very cool technical achievement of the trap (I'll have to see if I can rewrite this for my Checkpoint FW system), there were one things I learned about good design from this article:

Eliminate mailto - makes sense. You should have an http based "send me a message system" - force a live person to type stuff in instead of letting a program pick out addresses.

Eliminating mailto alone would probably help in mot of my spam problems (as I have my "contact me" address right on the first page).

Re:Elements of good design I'd missed

I put my email address in a jpeg image. Haven't found a spambot yet that can decipher that.

Slashbot

"I have a truly marvelous demonstration of this proposition which this bandwidth is too narrow to transmit."

Block? Are you kidding?

Why on Earth would you like to block a spambot? So it doesn't get any more useful addresses?
No way, man.
If you realize you're serving to a bot, go on serving. Each time the bot follows the "next page" link, you /give/ it a next page. With a nicely formatted [e-mail], where words and nums are random.
Give it thousands, millions of addresses this way.

Re:Block? Are you kidding?

Add a couple of sleep(20); into the cgi script that generates the bot fodder. The bot will still stay busy waiting for your webserver's response, but your script will exactly consume zero resources.

Zero resources, except for memory.

A much better solution would be to point the bot at a set of "servers" with IP addresses where you're running a stateless tarpit.

Re:Block? Are you kidding?

This isn't such a good idea - for every random (non-existent) domain that you generate, a root DNS server will be queried when an email is sent to this address, which increases the load on the root servers, which is generally a bad thing. How about instead, returning pages with the email address abuse@domain-that-spambot-is-coming-from all over them...

Re:Block? Are you kidding?

- for every random (non-existent) domain that you generate, a root DNS server will be queried when an email is sent to this address, which increases the load on the root servers, which is generally a bad thing.

Why is this a bad thing? They are owned by Verisign.

How about instead, returning pages with the email address abuse@domain-that-spambot-is-coming-from all over them...

This is also a good idea. In fact, I have a script which does a traceroute to the IP of the bot, and then looks up the admin contact using whois for the last couple of hops, and returns these. Oh, and for additional fun, throw in a couple of addresses of especially loved "friends"...

Re:Block? Are you kidding?

I agree. And, come on, how much technology do you need?

This is my solution to stopping spambots. It's in a JavaServlet technology and I am posting it here to prevent my company's site from being slashdotted. It does not prevent the spammer from harvesting emails it just slows them down.... a lot :) If everyone had a script like this, spambots would be unusable.

Feel free to use the code in anyway you please (LGPL like and stuff)

Put robots.txt in your root folder. Content:

User-agent: *
Disallow: /members/

Put StopSpammersServlet.java in WEB-INF/classes/com/parsek/util:

package com.parsek.util;
// Slashdot lameness filter trick... sklj lijef oiwej goweignm lkjhg woeèi weoij woefh woegih weoigj woefm weoikjf woeifh woefhpweifjwopejf pw
// Slashdot lameness filter trick... flk joweij pgwej pweof ,mpeof ,mpweorj pweomfwpegj pwehg woeigh owèefij woeij eogih oibhwepoi upeorw wpeo
// Slashdot lameness filter trick... fkjew fiwje spbojkwe gkwpeori wpbv-j wpeofksweok pweorjsw eigjhwoeifj pweorj wepoj wepfomwe fpmwoe fpowe
// Slashdot lameness filter trick... epoiw epw0 w'pg wpoe wpeom, wpog wepfoiwpeor kwpeof, wpobm wepofkwpeofk wopvf,w bowkpeoirf pwoef,mwepof p
// Slashdot lameness filter trick... vlwkepo wesp ibebemwf èsdm fèefo.bp kwèpef èlfk èeofsw èegjwegoweofiw peok èglks dgèlksdfèokwe ofèkwe èfoe
import java.io.File;
import java.io.StringWriter;
import javax.servlet.ServletContext;
import java.net.URL;
import java.util.Enumeration;
import java.lang.reflect.Array;
public class StopSpammersServlet extends javax.servlet.http.HttpServlet {
private static String[] names = { "root", "webmaster", "postmaster", "abuse", "abuse", "abuse", "bill", "john", "jane", "richard", "billy", "mike", "michelle", "george", "michael", "britney" };
private static String[] lasts = { "gates", "crystal", "fonda", "gere", "crystal", "scheffield", "douglas", "spears", "greene", "walker", "bush", "harisson" };
private String[] endns = new String[7];
private static long getNumberOfShashes(String path) {
int i = 1;
java.util.StringTokenizer st = new java.util.StringTokenizer(path, "/");
while(st.hasMoreTokens()) { i++; st.nextToken(); }
return(i);
}
// Respond to HTTP GET requests from browsers.
public void doGet (javax.servlet.http.HttpServletRequest request,
javax.servlet.http.HttpServletResponse response)
throws javax.servlet.ServletException, java.io.IOException {
// Set content type for HTML.
response.setContentType("text/html; charset=UTF-8");
// Output goes to the response PrintWriter.
java.io.PrintWriter out = response.getWriter();
try {
ServletContext servletContext = getServletContext();
endns[0] = "localhost";
endns[1] = "127.0.0.1";
endns[2] = "2130706433";
endns[3] = "fbi.gov";
endns[4] = "whitehouse.gov";
endns[5] = request.getRemoteAddr();
endns[6] = request.getRemoteHost();
String query = request.getQueryString();
String path = request.getPathInfo();
out.println("<html>");
out.println("<head>");
out.println("<title>Members area</title>");
out.println("</head>");
out.println("<body>");
out.println("<p>Hello random visitor. There is a big chance you are a robot collecting mail addresses and have no place being here.");
out.println("Therefore you will get some random generated email addresses and some random links to follow endlessly.</p>");
out.println("<p>Please be aware that your IP has been logged and will be reported to proper authorities if required.</p>");
out.println("<p>Also note that browsing through the tree will get slower and slower and gradually stop you from spidering other sites.</p>");
response.flushBuffer();
long sleepTime = (long) Math.pow(3, getNumberOfShashes(path));

do {
String name = names[ (int) (Math.random() * Array.getLength(names)) ];
String last = lasts[ (int) (Math.random() * Array.getLength(lasts)) ];
String endn = endns[ (int) (Math.random() * Array.getLength(endns)) ];
String email= "";

double a = Math.random() * 15;
if(a if(a if(a if(a if(a if(a if(a if(a if(a if(a if(a if(a if(a email = email + "@" + endn;

out.print("<a href=\"mailto:" + email + "\">" + email + "</a><br>");
response.flushBuffer();

Thread.sleep(sleepTime);

} while (Math.random()
out.print("<br>");
do {
int a = (int) (Math.random() * 1000);
out.print("<a href=\"" + a + "/\">" + a + "</a> ");
Thread.sleep(sleepTime);
response.flushBuffer();
} while (Math.random() out.println("</body>");
out.println("</html>");

} catch (Exception e) {
// If an Exception occurs, return the error to the client.
out.write("<pre>");
out.write(e.getMessage());
e.printStackTrace(out);
out.write("</pre>");
}
// Close the PrintWriter.
out.close();
}
}

Put this in your WEB-INF/web.xml

<servlet>
<servlet-name>stopSpammers</servlet-name& gt;
<servlet-class>com.parsek.util.StopSpammersS ervlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>stopSpammers</servlet-name& gt;
<url-pattern>/members/*</url-pattern>
</servlet-mapping>

Here you go. No PHP, no APache, no mySQL, no Perl, just one servlet container.

Ciao

Re:Block? Are you kidding?

Way too much work. Here's similar Escapade [escapade.org] code:

<QUIET ON>
<html><head><title>Members area</title></head><body>
<p>Hello random visitor. There is a big chance you are a robot collecting mail
addresses and have no place being here.
Therefore you will get some random generated email addresses and some random links
to follow endlessly.</p>
<p>Please be aware that your IP has been logged and will be reported to proper
authorities if required.</p>
<DBOPEN "SpamFood", "localhost", "login", "password">
<FOR I=1 TO 100 STEP 1>
<SQL select * from names order by rand() limit 1>
<LET FN="$Name">
</SQL>
<SQL select * from lasts order by rand() limit 1>
<LET LN="$Last">
</SQL>
<SQL select * from addresses order by rand() limit 1>
<LET AD="$Address">
</SQL>
<a href="mailto:$FN.$LN@$AD">$FN.$LN@$AD</a> <br>
</FOR>
</body>
</html>

How I track spammers using PHP

I did something rather low-tech: I created a "Contact Us" page on my web server that has an automatically-generated address at the bottom. It says, "Note: The address [e-mail] is not a valid contact address. It's just here to catch spammers." The number is actually the current UNIX timestamp, so I know exactly who grabbed this mail address and sent me mail.

As it turns out, I really haven't received that much mail to this address. About the only mail I've ever received to it is someone from trafficmagnet.net, who tells me that I'm not listed on a few search engines and that I can pay them to have my site listed. I need to send her a nasty reply saying that I don't care about being listed on Bob's Pay-Per-Click Search Engine, and that if she had actually read the page, she would have noticed that she was sending mail to an invalid address. Besides, the web server is for my inline skate club and we don't have a $10/month budget to pay for search engine placement.

I think I've received more spam from my Usenet posting history, from my other web site, and from my WHOIS registrations than I've received from the skate club web site.

Hammered already....

From the website:
The Problem: Spambots Ate My Website

s/Spambots/Slashdot/

re: spidertrap

My PHP spider-trap [blibbleblobble.co.uk] - See an infinity of email addresses and links in action!

removing mailto: a bad solution

Removing mailto: links is a bad solution to the problem. It might be the only solution, but it is bad.

I hate the editor in my web browser. No spell check (and a quick read of this message will prove who diasterious that is to me), not good editing ability, and other problems. By contrast my email client has an excellent editor, and a spell checker. Let me pull up a real mail client when I want to send email, please!

In addition, I want people to contact me, and not everyone is computer literate. I hang out in antique iron groups, I expect people there to be up on the latest in hot tube ignition technology, not computer technology. To many of them computers are just a tool, and they don't have time to learn all the tricks to make it work, they just learn enough to make it do what they want, and then ignore the rest. Clicking on a mailto: link is easy and does the right thing. Opening up a mail client, and typing in some address is error prone at best.

Removing mailto: links might be the only solution, but I hope not. So I make sure to regualrly use spamcop [spamcop.org].

A better solution: obfuscate the mailto: link

Write some of your email address using html code for the ascii characters, like &#36 &#35 114 for "r".
(Yes, I've posted about this before [slashdot.org], but it does work for me.) Browsers render it so users get the address they want, but spambots try to grab it from the raw html and get something meaningless.

Re:A better solution: obfuscate the mailto: link

Some spambots will render that correctly. Less likely, though, is if they'll render an email that has had this [jracademy.com] done to it: it's encrypted through javascript.

It is a rather impressive piece of work. Uses honest-to-god RSA.

You could also encrypt all email addresses, and then in your spambot trap, put really really CPU intensive javascript. You'll win either way: either the spambot doesn't do javascript, and it won't get your addresses, or it does do javascript, and they've just spent an eternity wasting time. It would work the same way as a tarpit, but it wouldn't eat nearly so many resources on your end.

If you're really clever, you could have the javascript do useful work, and then have the results of that work encoded into links in the page. You could then retrieve the results when the spider follows the link.

There was an idea called hashcash floating arount a while back. The idea was that an SMPT server would refuse to deliver email if the sender didn't provide a hash collsion of so many bits to some given value. The sender has to expend way assymetrically more resources to generate the collision than it takes the reciever to check it. That way on can impose a cost on sending a lot of email. It's not so much to be a burden on ordinary users, but if you need to send thousands of emails, it will add up.

Similar to how the new ORBZ works?

After the Battle Creek incident with ORBZ, the maintain changed the way it worked; instead of being pro-active on checking for open relays, he now has a 'honeypot' like system where a unique email address that isn't directly visible on the site but still may be harvested by a spam bot. Any server that sends email to that address is automatically added to The List. Mail server admins that believe that they should not be on this list can argue their case to remove their server.

Re:Similar to how the new ORBZ works?

he now has a 'honeypot' like system where a unique email address that isn't directly visible on the site but still may be harvested by a spam bot. Any server that sends email to that address is automatically added to

This is the same method I have been using for a while. I have an e-mail account called "cannedham" that I had posted on several web sites as a mailto: anchor on a 1x1 pixel graphic. Any e-mail sent to that address updates my Postfix header_checks file to protect the rest of my accounts. It works like a charm.

Take a look in the mirror

Superior Labs spambot_trap mirror [superiorlabs.com]

-Spack

A tip

Here's a tip for those of you writing spambot traps... How about not blindly responding to the faked Return-Path address?

Now that should be illegal. You people whine about your 10 spams a day, try 10,000 from 2000 different email addresses. Idiot postmasters should be caught and jailed.

he suggests formmail, another spam tool

Interestingly within the article he suggests hiding your e-mail addresses by making a feedback page. One of the programs that he suggests is formmail, and he links to Matt's original version.

formmail itself (even the most recent version) can still be abused by spammers to use your webserver as a bulk mail relay - see the advisory at [monkeys.com]
http://www.monkeys.com/anti-spam/formmail-adviso ry . df

It's a shame he didn't suggest the more robust formmail replacement at nms [sourceforge.net] which is maintained, and attempts to close all the known bugs and insecurities.

Removing the Mailto: may not be the best plan..

I've found that a lot of people just won't send email if there's not a link to facillitate it. I've become rather fond of using javascript to write the address to the page. Spambots read the source so they don't piece the address together but *most* browsers will still do it right. Just use something like:

<script>document.write("<A CLASS=\"link\" HREF=\"mailto: " + "myname" + String.FromCharCode(64) + "mydomain"</script>

Seems to work fine. Anyone know of any reason it shouldn't, or have any other way to keep down spam without totally removing the Mailto: ? I know this won't work with *every* browser, but it beats totally removing mail links. And I don't think spammers can get it without having a human actually look at the page...

Re:Removing the Mailto: may not be the best plan..

hell, go one step further:

<img src="myemailaddress.jpg" alt="me at domain dot com">

that way people who use browsers that speak (ie. the blind) would still hear your address correctly, so long as spambots don't start to pick up on the spelling out of "at" and "dot".

Similar setup without SQL requirements

My setup (catches some of the more commonly used spambots) uses mod_rewrite to send spammers to a trap.
Setup details at http://www.bero.org/NoSpam/isp.php [bero.org]

Another way to stop spambots

Have your page linked on slashdot! Page gets slashdotted, problem solved.

my spambot trap

The page is already slashdoted. Here is a little
script that traps bots (and others) that use your robots.txt
to find directories to look through. Requires an .htaccess file with mod_rewrite turned on

robots.txt
#################

User-agent: *

Disallow: /dont_go_here
Disallow: /images
Disallow: /cgi-bin

dont_go_here/index.php
############

$now = date ("h:ia m/d/Y");
$IP=getenv(REMOTE_ADDR);
$host=getenv(R EMOTE_HOST);
$your_email_address=you@whatever;

$ban_code =
"\n".
'# '."$host banned $now\n".
'RewriteCond %{REMOTE_ADDR} ^'."$IP\n".
'RewriteRule ^.*$ denied.html [L]'."\n\n";

$fp = fopen ("/path/to/.htaccess", "a");
fwrite($fp, $ban_code);
fclose ($fp);

mail("$your_email_address", "Spambot Whacked!", "$host banned $now\n");

Other options..

A pretty good article, but being able to install modules into Apache may not be the best situation for everyone who wants to stop Spambots..

Shameless plug, but I've got an ongoing series in the Apache section of /. that deals with easy ways that administrators *and* regular users can keep Spambots off their sites:
Stopping Spambots with Apache [slashdot.org]
and
Stopping Spambots II - The Admin Strikes Back [slashdot.org]

Just some more options and choices to help people out!

Take this one step further...

There's a spam-blacklist, so how about a spambot-blacklist?

You'd have a standardized spambot trap (like the one described in the article) on various webservers. The new spambot info could go into a "New SpamBots" database (which wouldn't be blocked). Once a day, the webserver would connect up with a central database and submit the new spambot info it's obtained. Then the server would download a mirror of the updated "SpamBots" database which it would use to block spambots.

The centralized SpamBots database would take all of the new SpamBot info every day and analyze them in some manner as to detect abuse of the system (ensuring that only true spambots are entered). E-mails could be fired off to the abuse/postmaster/webmaster for the offending IP address. Finally, the new SpamBot info would be integrated into the regular SpamBot database.

This way you'd be able to quickly limit the effectiveness of the Spambot-traps across many websites.

Attn Spambot Authors

Dear Spambot Authors,

Thanks again for your interest. I hope that we were able to help you write the spambots of the future that will be able to detect and sidestep as many of the above protection schemes as possible. We tried to work all of our knowledge into one convienient thread for your development team to peruse.

Thanks for your interest in SlashDot, home of too much information.

What I use

Take a look at these two bits of code from http://www.slickhosting.com/contact.shtml [slickhosting.com] :

<A HREF="mailto:hosting%40slickhosting.com"
onMouseO ver="window.status='mailto:hostingsli ckhosting.com';return true;"
onMouseOut="window.status='';">hostingslic khosting.com</A>

<!-- Spam trap
abuse@ (your domain) HREF="mailto:abuse@ (your domain) "
root@ (your domain) HREF="mailto:root@ (your domain) "
postmaster@ (your domain) HREF="mailto:postmaster@ (your domain) "
[e-mail] HREF="mailto:[e-mail]"
-->

Don't stop spambots, feed them with Sugarplum

I don't stop spambots, I feed them. I feed them phony email addresses and addresses of spammers (gathered from places such as my fake /cgi-bin/formmail.pl). I use http://www.devin.com/sugarplum/ [devin.com], mentioned before on /. to dish it out!

the danger of mailing lists.. esp. SuSE user list

Another way your e-mail address can be susceptible to spambots is if you participate in any mailing list. If the administrator decides to archive the list on a website, in many cases the email addresses of the participants will be there in plain text. I found this out after doing a google search for my own email address and having it turn up on

the SuSE web site [suse.com]. I sent an e-mail asking that they do a regsub on the archive to substitute the '@' with [at] or something similar. That was more than six months ago and the SuSE website admin still hasn't done it.

New Program - Mailwasher

Speaking of spam, I've come across this new program called mailwasher. You can check your mail while it's still on the server, and then - get this - fake a bounced message. There are probably other programs that do this, but this is the first one I've heard of.

Anyway, AFAIK, it's WinBlows only, and available at http://www.mailwasher.com [mailwasher.com], although right now it seems the site is down, all I get is a 404!