Обход защиты персональных файрволов

Дата публикации:
08.12.2004
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Уязвимые версии: большинство персональных файрволов

Описание:
Вредоносное программное обеспечение может реализовать атаку типа shatter на разрешенное файрволом GUI приложение и выполнить произвольный код в его контексте. После этого вредоносное программе обеспечение получает возможность взаимодействовать с внешними сетями в обход политик безопасности файрвола.

Решение: решение не существует на данный момент.

Источник:

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.


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.


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.


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.



So, attack is very simple:
1. Trojan finds trusted application and appropriate.
2. Trojan inserts shellcode in selected window


...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...


3. Afterward trojan founds shellcode address, and transfer control to the shellcode.

It's not a problem, because

...even the most obscure of messages can be used to make a process execute code that it was not intended to run.


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.

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