Microsoft Browser Slips Up On SSL Certificates - Report

[Howell, Paul]

At http://www.newsbytes.com/news/01/173217.html


Microsoft Browser Slips Up On SSL Certificates - Report 
 
By Steven Bonisteel, Newsbytes
KOLN, GERMANY,
26 Dec 2001, 10:53 AM CST


 With the online holiday-shopping rush already over, some consumers might be
chagrined to learn now how easy it is for hackers to trick Microsoft's
[NASDAQ:MSFT] Internet Explorer browser into accepting bogus certificates
for what should be secure access to e-commerce Web sites. 
Germany-based E-matters, a Web development company, announced Saturday that
it had found a hole in IE's authentication of secure sockets layer (SSL)
exchanges that allows Webmasters to use stolen or expired SSL certificates. 
  
At least one subsequent report by security watchers has suggested the
problem may be specific to Windows versions of the IE browser. 

SSL certificates are sold - and digitally signed - by companies such as
Verisign and are intended to ensure the identity of the Web servers and the
companies for which they are issued. 

Stefan Esser of E-matters said in postings to computer security mailing
lists that he notified Microsoft on Nov. 26 that IE browsers version 5.0,
5.5 and 6.0 were easily duped into accepting invalid certificates, but was
told that fixing the problem would take some time. 

Pages posted by Esser on the E-matters Web site demonstrated how hackers can
use an SSL link to an image on an uncertified server to force the IE browser
to later establish a secure session without alerting the user that the
secure certificate on the site is for another Internet domain. 

Newsbytes' own tests confirmed Esser's report that the bug also allows Web
sites to use expired - but otherwise valid - secure certificates without
complaints from IE. 

Using Netscape 4.7 and 6.1 and Opera 5.1, the same test pages caused those
browsers to warn users that the certificates might be bogus. 

The encryption of data in SSL transactions is essentially the same whether
the certificates are legitimate, bogus, or non-existent. However, legitimate
e-commerce sites pay companies such as Verisign to endorse their
certificates in part because security-warning messages from browsers do
little to inspire confidence among consumers. 

In addition, some consumers may be keen to know if the outfits accepting
their credit card numbers through SSL-protected Web pages are probably who
they say they are. 

Esser found that IE won't complain about embedded links (such as those for
pictures) to bogus SSL connections when those links are on pages served up
without SSL and the certificates are at least signed by a legitimate
authority (like Verisign). 

He said it appears as though IE maintains that level of trust if a Web
surfer then establishes a typical SSL session with the same bogus server. 

Esser noted that a user who actually asks his or her browser to display
certificate information will see that the domain for which the certificate
was issued does not match the site they are visiting, or that the
certificate has expired. 

However, he argued that "only paranoid people" would perform such checks
without first being alerted to a potential problems by their browsers. 

The hole appears to establish a use for stolen secure certificates, which
have been considered difficult to use without most Web visitors being
alerted. 

In a sophisticated exploit, Esser said, a hacker in a possibly rare position
to divert SSL traffic could pose as a legitimate e- commerce site and hijack
transactions without most shoppers knowing. 

The IE problem also appears to allow otherwise legitimate outfits to
continues using expired certificates - or certificates they were issued for
other domains - with only customers who don't use the IE browser learning of
that questionable frugality. 

The E-matters report on the issue can be found here:
http://security.e-matters.de/advisories/012001.html