ie.cert.attack.txt

`  
e-matters GmbH  
www.e-matters.de  
  
-= Security Advisory =-  
  
  
  
Advisory: Interner Explorer HTTPS certificate attack  
Release Date: 2001/12/22   
Author: Stefan Esser [[email protected]]  
  
Application: Microsoft Internet Explorer 5.0/5.5/6.0  
Severity: Vulnerability in IE's SSL Certificate handling allows  
undetected SSL Man-In-The-Middle attacks  
Risk: Very High  
Vendor Status: Notified  
Reference: http://security.e-matters.de/advisories/012001.html  
  
  
  
Overview:  
  
A flaw in Microsoft Internet Explorer allows an attacker to perform  
a SSL Man-In-The-Middle attack without the majority of users recognising  
it. In fact the only way to detect the attack is to manually compare the  
server name with the name stored in the certificate.  
  
For a basic introduction into SSL MIM attacks I recommend reading:  
  
Phrack #57 - Hang on, Snoopy (by stealth)  
http://www.phrack.org/show.php?p=57&a=13  
  
  
Details:  
  
There is a flaw in the way IE checks HTTPS objects that are embedded into   
normal HTTP pages. According to my tests IE does only check if the certi-  
ficate of the HTTPS server is properly signed by a trusted CA but totally  
ignores if the cert was issued onto the correct name or has already ex-  
pired. This is in fact not dangerous because the user considers HTTPS   
objects embedded in a HTTP page not secure. The problem is that IE flags  
the certificate as trusted and caches this certification trust until your  
browser session ends. That means once you visited a normal http page that  
included an image from the MIMed SSL Server, IE will not warn you about   
an illegal site certificate as long the certificate was signed by f.e.   
Verisign.  
  
A possible scenario would be:  
  
Hacker runs a MIM attacking tool for HTTP/HTTPS in the subnet of your   
site. The HTTP part of the tool auto appends  
  
<img src="https://www.yoursite.com/nonexistent.gif" width=1 height=1>  
  
to any html page that is returned to your customer's browser and the   
HTTPS part presents his browser a valid but stolen certificate for   
www.shop.com. IE will only check if the cert was signed by a trusted CA  
when trying to display the image and won't compare the name inside the   
cert or check the expiration date. If your customer now tries to login  
to your site via HTTPS IE will consider the cert trustworthy without   
checking it again. Your customer will only be able to determine that he  
was just tricked by manually checking the servername in the cert. But  
you can be sure that only paranoid people would check. The majority of  
people don't even know how they can do so. Imagine the hacker stole the  
cert from "yoursite.de"... How many users of "yoursite.com" would not  
trust a cert that was issued on "yoursite.de". The average user does   
not know anything about SSL than it's making his payment "secure".  
  
  
Proof of Concept:  
  
A proof of concept webpage was put up at http://suspekt.org. Clicking   
onto the "To the secure page..." link will send your browser to   
https://suspekt.org without IE warning you that the certificate was not  
issued onto that server.  
  
This is not a MIM but it has the same effect: IE will tell you a page is  
secure although the certificate is illegal and its possible for a third  
party (anyone who owns the given certificate) to decrypt your traffic in  
realtime.  
  
  
Vendor Response:  
  
26 November 2001 - Microsoft was informed about this vulnerability  
27 November 2001 - Proof of concept page got visited by lots of MS IPs  
01 December 2001 - Microsoft informed us with a standard reply that  
they have received the advisory  
12 December 2001 - Microsoft was informed that were going to release   
the advisory within the next 3 days  
13 December 2001 - Microsoft asked us to wait because the issue is   
complex due to the fact a lot of cryptography   
is involved  
21 December 2001 - Microsoft sent an update: no patches yet,   
still a complex issue  
  
  
Conclusion:  
  
Until today Microsoft did not release a patch, they had nearly a month   
time to fix the bug. Instead they call it a very complex issue. Because  
I don't know the source code of the Internet Explorer I cannot check the  
validity of these claims, but from my point of view fixing this missing  
check is just a matter of copy and pasting a few lines. Unfortunately it  
is christmas time and especially during the last month millions of cus-  
tomers where buying christmas presents on the internet all around the  
world. That means millions of customers were shopping with insuffient   
protection of their private data. Because there are no patches out yet,  
I strongly recommend that you use Mozilla, Opera or another non MS brow-  
ser to do your internet banking or shopping these days. If you think   
(for whatever strange reason) that you need the Internet Explorer,   
ensure that the certificate is the correct by comparing the servername  
in the certificate with the one in your browser...   
  
  
GPG-Key:  
  
http://security.e-matters.de/gpg_key.asc  
  
pub 1024D/D19C5835 2001-11-26 e-matters GmbH - Securityteam   
Key fingerprint = DD27 8C4B CEDE 41A9 5766 39BA AF65 B19C D19C 5835  
  
  
Copyright 2001 Stefan Esser. All rights reserved.  
  
  
--- Packet Storm ---  
  
  
UPDATE: IE https certificate attack  
  
Date: 2001/12/25  
  
This morning i was googling through the web and found out that  
the issue is not that new for Microsoft.  
If you compare  
http://www.acros.si/aspr/ASPR-1999-12-15-1-PUB.txt  
with my advisory at  
http://security.e-matters.de/advisories/012001.html  
you can see that the same bug was reported 2(!) years ago to  
microsoft. At that time (or better half a year later) Microsoft  
released the patches for that vulnerability that fixed the  
bug within IE 4.0 and the early versions of IE 5.0.  
The Microsoft Security Bulletin (MS00-039) clearly states that  
IE 5.01 SP1 and IE 5.5 are not vulnerable.  
That means, that one of the "security patches" that Microsoft  
released since that date reimplemented the bug and made all  
IEs vulnerable again.  
  
Stefan Esser  
  
  
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