Despite the severity of some of the vulnerabilities posted by Liu Die
Yu, such as the ability for system compromises, it is relatively easy to
mitigate against the impact and even prevent them from having any effect
at all.
Much ado has been made about those vulnerabilities and they have been
covered in numerous places such as Forbes, NY Times and CNN. What this
tells me is that we need a radically different approach than the status
quo. One such approach is to put more emphasis on education and secure
coding, so that we can reliably prevent future threats. Another such
approach is to focus on proactive security measures that prevent
vulnerabilities and design flaws from having any effect in advance,
prior to their discovery and publication. We can recognize the common
pathways that these vulnerabilities rely on and act accordingly.
When I attended the NTBugtraq Retreat earlier this year, most of the
attendees were surprised to hear that I am using Internet Explorer on a
daily basis, particularly since I should know how vulnerable it can be
at any given time. I surf with JavaScript and ActiveX enabled, see flash
movies and play Java games, but despite this I am not vulnerable [0] to
a single command execution vulnerability or system compromise through
Internet Explorer.
How, you might ask? Simple, I have locked down the My Computer security
zone on my installations [1].
Each and every command execution vulnerability in Internet Explorer over
the last few years have all depended on the functionality of local
security zones. Whenever you are crafting an exploit, you want to
navigate a window object to a local security zone, inject some scripting
or HTML into the window object and subsequently use the features of the
local security zone to execute your payload. Properly locking down the
My Computer zone prevents all of these from having any effect.
However, changing the Internet Explorer security zone settings is not a
nimble task. Despite being partly split after IE4, the functionality of
Windows Explorer and Internet Explorer is still very tightly interwoven.
If you are not careful you WILL cause your system to malfunction and no
longer open Explorer folders, launch applications or even boot into
Windows properly. You need to strike a very sensible balance.
During the course of our research, we crafted and tested solutions to
this problem on tens of thousands of installations and have beta tested
on thousands of users, and have incorporated the results into our FREE
constantly updated Proactive Threat Mitigation application that goes by
the name of Qwik-Fix(r) ( www.pivx.com/qwikfix/ ). Our beta users were
never affected by Blaster, HTAExploit or MiMail - to name a few.
Now, let's analyze the vulnerabilities Liu Die Yu posted on November
25th [2], as there was not much details in the post.
"1stCleanRc" is not a vulnerability of its own, but an example exploit
detailing how to combine the "MhtRedirParsesLocalFile",
"BackToFramedJpu" and "MhtRedirLaunchInetExe" vulnerabilities. The same
goes for "execdror6" which is an example exploit that relies on the
"LocalZoneInCache" vulnerability, as well as "LocalZoneInCache" which is
a demonstration of using "threadid10008".
This leaves us with 5 vulnerabilities to analyze:
MhtRedirParsesLocalFile is designed to display and parse a locally
residing file of any plaintext format in an IFRAME. On most of our
installations we could only reproduce the display part. Still, being
able to display a locally residing file in a window object is
specifically prohibited by IE6 SP1.
MhtRedirLaunchInetExe expands a bit on the capabilities of the codeBase
vulnerability. Microsoft fixed codeBase in the Internet Zone, but left
it in the My Computer zone. As such, MhtRedirLaunchInetExe simply makes
it one step easier to bundle HTML, Script and executable payload in the
same file.
BackToFramedJpu lets you inject javascript URLs into the history and
have them executed in the context of the target window object.
HijackClickV2 lets you hijack clicks and target them at some system
dialogs. You will have to know the location of those.
Threadid10008 is intended to download an HTML file to the TIF and
subsequently display and parse it. It could not be reproduced on all our
systems, but it does help leverage entry into a local security zones on
the installations it worked on.
Locking down the My Computer security zone prevents all of the 3
exploits by mitigating the effects of the remaining vulnerabilities
substantially, while still allowing a usable surfing experience.
As a final comment, I do believe that vulnerability researchers should
notify vendors of potential vulnerabilities and give them some time to
fix these before exposing the public to the dangers of those
vulnerabilities. Posting demonstratory proof-of-concept code has served
to apply pressure in the past towards unresponsive vendors, but not
giving the vendors any chance to respond at all in the first place is
simply irresponsible and jeopardizes the security of the Internet as a
whole.
References:
[0] Qwik-Fix(r)
http://www.pivx.com/qwikfix/
[1]
Description of Internet Explorer Security Zones Registry Entries
http://tinyurl.com/ubfq
[2] Post by Liu Die Yu
http://tinyurl.com/x8qx
Regards
Thor Larholm
Senior Security Researcher
PivX Solutions
24 Corporate Plaza #180
Newport Beach, CA 92660
http://www.pivx.com
thor@pivx.com
949-231-8496
PivX defines "Proactive Threat Mitigation". Get a FREE Beta Version of
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