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Bypass personal firewall application protection . Again.
(c)oded by offtopic (offtopic@mail.ru) 2004
Special thank to 3APA3A for links to the debuggers for Windows.
<quote src= http://www.security.nnov.ru/advisories/bypassing.asp?l=EN >
Personal firewall usually restricts access to network to the list of
allowed application. In addition, integrity of these applications is
controlled to prevent code insertion into executable file. It makes it
impossible to install trojan application with direct network access.
</qoute>
Modern personal firewalls hook such unsafe API calls like WriteProcessMemory
CreateRemoteThread, and controls modification of trusted application code. Some
personal firewalls even catch CAT+ sometimes.
So we got protected high-privileged application, which can communicate with
network, low-privileged application trojan, and personal firewall as access
control system.
The best way for bypass any accesses control in windows is a SHATTER attacks.
Because most if not all of high-privileged applications use GUI trojan can use
window messages to modify application memory and execute code in the context of
trusted application.
<quote src= http://security.tombom.co.uk/shatter.html >
Any application on a given desktop can send a message to any window on the same
desktop, regardless of whether or not that window is owned by the sending
application, and regardless of whether the target application wants to receive
those messages. There is no mechanism for authenticating the source of a
message; a message sent from a malicious application is indistinguishable from a
message sent by the Windows kernel. It is this lack of authentication that we
will be exploiting, taking into consideration that these messages can be used to
manipulate windows and the processes that own them.
</qoute>
So, attack is very simple:
1. Trojan finds trusted application and appropriate.
2. Trojan inserts shellcode in selected window
<quote src= http://www.google.com/search?q= input+-+if+crafted '>
+This is generally a very easy thing to do, as any user-supplied input if
crafted
correctly can be interpreted as a sequence of valid CPU instructions+
</quote>
3. Afterward trojan founds shellcode address, and transfer control to the
shellcode.
It s not a problem, because
<quote src=
http://www.securityassessment.com/Papers/Shattering_By_Example-V1_03102003.pdf >
+even the most obscure of messages can be used to make a process execute code
that it was not intended to run.
</quote>
I don t experiment on this too much but several of widely used personal
firewalls are tested and vulnerable. If any vendors need addition details, they
can contact me.
Thanks for your attention and sorry for my English.
(c)oded by offtopic@mail.ru
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