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Re: Linux Kernel Exploits / ABFrag
From: huang po <huangpo () hehe com>
Date: 17 Oct 2002 20:55:32 -0000

In-Reply-To: <3DAEAB3000000735 () www zipmail com br>

From: Peter Pentchev (roam () ringlet net)
Subject: Re: *BSD remote kernel-level (TCP/IP stack)
vulnerability! - ABFrag.c 

Newsgroups: fa.freebsd.bugs
Date: 2002-09-23 07:04:01 PST

On Sun, Sep 22, 2002 at 03:51:54PM +0300,
cizbasa () info uvt ro wrote:

First of all this is hear-say, but being from a
reliable source (imho),
here it is:

There supposedly is an exploit named ABFrag.c in the
wild that affects the
TCP/IP stack on *BSD systems, providing remote root
shell to the attacker.

There have been various rumours of exploits using
fragmented packets for
the TCP/IP stacks of various OS's in the past few
years.  I personally
find them very hard to believe: the TCP/IP stack is
part of the kernel,
and while it may be theoretically possible that the
fragmented packets'
handling is a bit off-base, it would be *very* hard to
write an exploit
that would perform a stack smash in the kernel, then
pass control to a
kernel routine that would start a userland process,
bind it to a
listening port, then make sure it starts up a shell. 
Mind you, I am not
saying that this would be impossible, just very, very,
*very* much
improbable :)  Even if it were true, it would be very
much more harder
to write so that it would affect *different* OS's: the
differences in
the TCP stacks are not that large, but significant for
at least this

The system of someone that I know has been rooted
using it (he was pasted
some lines from his /etc/shadow as proof).

Well, first of all, I assume you mean
/etc/master.passwd, because there
is no /etc/shadow in FreeBSD :)

Second, are you absolutely sure that your
acquaintance's system was not
"rooted" using another exploit?  Apache+OpenSSL and
telnetd come to mind
immediately, there were a couple of others in the past
few months.


Peter Pentchev  roam () ringlet net     roam () FreeBSD org
PGP key:        http://people.FreeBSD.org/~roam/roam.key.asc
Key fingerprint FDBA FD79 C26F 3C51 C95E  DF9E ED18
B68D 1619 4553

exist rumors about this exploit since 3 months. The
archive aparently exp=
an imperfection in the TCP Sync (i dont know details
about problem). Due
to rumors, exist more two exploits for the problem
(maybe fake). 
Some forums like ByteRage's PRIVATE forum was
dicussing it in private (it=

is bad to kids/defacers, but good to security
professionals and admins).
Thanks to you and all list readers...
Nilson Gomes

-- Mensagem original --

   Today I had a rather strange experiance. At about
4:30 pm GMT my
IDS began reporting strange TCP behaviour on my
network segment. As I
was unable to verify the cause of this behaviour I
was forced to remove
the Linux box that I use a border gateway and traffic
monitor - at no sm=
cost to my organization - the network is yet to be
After a reboot and preliminary analysis I found the
binary ABfrag sittin=
in /tmp. It had only been created minutes before.
Setting up a small sandbox I ran the program and was
presented with the


ABfrag - Linux Kernel ( <=3D 2.4.20pre20 ) Remote
Syncing exploit

Found and coded by Ac1db1tch3z - t3kn10n, n0n3 and

Unlicensed usage and/or distribution of this program
carries heavy fines=

and penalties under American, British, European and
International copyri=
Should you find this program on any compromised
system we urge you to de=
this binary rather than attempt distribution or
analysis. Such actions
be both unlawful and unwise.

invalid key  

I remembered, vaguely - I sift through a lot of
security mail each day,

talk of a rumoured Linux kernel exploit circulating
among members of the=

underground. On the advice of some friends in
law-enforcement I joined
channels #phrack and #darknet and tried to solicit
some information rega=
alleged exploit. Most people publicly attacked me for
my neivette but tw=
contacted me via private messages and informed me
that the "ac1db1tch3z"=

were bad news,
apparently a group of older (mid 20's) security
guru's, and that I shoul=
delete the
exploit and forget I ever knew it existed.
However, somthing twigged my sense of adventure and
prompted me to try
get this out
to the community.

Any help or information regarding this will be of
great help.

I have attached the binary although it appears to be
encrypted and passw=
I wish
any skilled programmers the best of luck in
decyphering it.


Daniel Roberts
Head Network Manager

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