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solve.py
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#!/usr/bin/env python3
## -*- coding: utf-8 -*-
##
## Jonathan Salwan - 2018-11-02
##
## This code solve the angry-reverser from the HackCon 2016 CTF.
##
## Output:
##
## $ time python3 solve.py
## [+] Loading 0x400040 - 0x400200
## [+] Loading 0x400200 - 0x40021c
## [+] Loading 0x400000 - 0x405d04
## [+] Loading 0x605d08 - 0x605f58
## [+] Loading 0x605d20 - 0x605ef0
## [+] Loading 0x40021c - 0x400260
## [+] Loading 0x405bb0 - 0x405bec
## [+] Loading 0x000000 - 0x000000
## [+] Hooking puts
## [+] Hooking printf
## [+] Hooking __libc_start_main
## [+] Hooking ptrace
## [+] Hooking __isoc99_scanf
## [+] Hooking exit
## [+] Starting emulation.
## [+] __libc_start_main hooked
## [+] argv[0] = yolomolo
## [+] scanf hooked
## [+] symbolizing scanf buffer
## [+] ptrace hooked
## [+] Solving condition at 0x402c31
## [+] Solving condition at 0x402ea4
## [+] Solving condition at 0x403111
## [+] Solving condition at 0x403380
## [+] Solving condition at 0x4035ed
## [+] Solving condition at 0x40385d
## [+] Solving condition at 0x403aca
## [+] Solving condition at 0x403d3c
## [+] Solving condition at 0x403fae
## [+] Solving condition at 0x40421c
## [+] Solving condition at 0x40448b
## [+] Solving condition at 0x4046ff
## [+] Solving condition at 0x40496d
## [+] Solving condition at 0x404be1
## [+] Solving condition at 0x404e4e
## [+] Solving condition at 0x4050bc
## [+] Solving condition at 0x40532d
## [+] Solving condition at 0x40559e
## [+] Solving condition at 0x4057e9
## [+] Solving condition at 0x405a20
## [+] printf hooked
## YAYY : 2684354496
## [+] Solving the last query to get the good serial...
## Serial is: HACKCON{VVhYS04ngrY}
## [-] Instruction not supported: 0x400579: hlt
## [+] Instruction executed: 4453
## [+] Emulation done.
##
## python3 solve.py 113.53s user 0.09s system 99% cpu 1:53.79 total
##
from __future__ import print_function
from triton import *
import random
import string
import sys
import os
import lief
TARGET = os.path.join(os.path.dirname(__file__), 'yolomolo')
DEBUG = True
SERIAL = str()
# The debug function
def debug(s):
if DEBUG: print(s)
# Memory mapping
BASE_PLT = 0x10000000
BASE_ARGV = 0x20000000
BASE_STACK = 0x9fffffff
# These instruction conditions must set zf to 1.
conditions = [
0x402C31,
0x402EA4,
0x403111,
0x403380,
0x4035ED,
0x40385D,
0x403ACA,
0x403D3C,
0x403FAE,
0x40421C,
0x40448B,
0x4046FF,
0x40496D,
0x404BE1,
0x404E4E,
0x4050BC,
0x40532D,
0x40559E,
0x4057E9,
0x405A20,
]
def getMemoryString(ctx, addr):
s = str()
index = 0
while ctx.getConcreteMemoryValue(addr+index):
c = chr(ctx.getConcreteMemoryValue(addr+index))
if c not in string.printable: c = ""
s += c
index += 1
return s
def getFormatString(ctx, addr):
return getMemoryString(ctx, addr) \
.replace("%s", "{}").replace("%d", "{:d}").replace("%#02x", "{:#02x}") \
.replace("%#x", "{:#x}").replace("%x", "{:x}").replace("%02X", "{:02x}") \
.replace("%c", "{:c}").replace("%02x", "{:02x}").replace("%ld", "{:d}") \
.replace("%*s", "").replace("%lX", "{:x}").replace("%08x", "{:08x}") \
.replace("%u", "{:d}").replace("%lu", "{:d}") \
# Simulate the printf() function
def printfHandler(ctx):
debug('[+] printf hooked')
# Get arguments
arg1 = getFormatString(ctx, ctx.getConcreteRegisterValue(ctx.registers.rdi))
arg2 = ctx.getConcreteRegisterValue(ctx.registers.rsi)
arg3 = ctx.getConcreteRegisterValue(ctx.registers.rdx)
arg4 = ctx.getConcreteRegisterValue(ctx.registers.rcx)
arg5 = ctx.getConcreteRegisterValue(ctx.registers.r8)
arg6 = ctx.getConcreteRegisterValue(ctx.registers.r9)
nbArgs = arg1.count("{")
args = [arg2, arg3, arg4, arg5, arg6][:nbArgs]
s = arg1.format(*args)
if DEBUG:
sys.stdout.write(s)
# Return value
return len(s)
# Simulate the putchar() function
def putcharHandler(ctx):
debug('[+] putchar hooked')
# Get arguments
arg1 = ctx.getConcreteRegisterValue(ctx.registers.rdi)
sys.stdout.write(chr(arg1) + '\n')
# Return value
return 2
# Simulate the scanf() function
def scanfHandler(ctx):
debug('[+] scanf hooked')
# Get arguments
arg1 = ctx.getConcreteRegisterValue(ctx.registers.rdi)
arg2 = ctx.getConcreteRegisterValue(ctx.registers.rsi)
# Fill scanf buffer with dummy inputs
ctx.setConcreteMemoryAreaValue(arg2, b"HACKCON{???????????}\n\x00")
# Symbolize 30 bytes
debug('[+] symbolizing scanf buffer')
for index in range(8, 19):
var = ctx.symbolizeMemory(MemoryAccess(arg2 + index, CPUSIZE.BYTE))
# Return value
return 21
# Simulate the ptrace() function
def ptraceHandler(ctx):
debug('[+] ptrace hooked')
# Don't care about ptrace :)
# Return value
return 0
# Simulate the puts() function
def putsHandler(ctx):
debug('[+] puts hooked')
# Get arguments
arg1 = getMemoryString(ctx, ctx.getConcreteRegisterValue(ctx.registers.rdi))
sys.stdout.write(arg1 + '\n')
# Return value
return len(arg1) + 1
# Simulate the strncpy() function
def strncpyHandler(ctx):
debug('[+] strncpy hooked')
dst = ctx.getConcreteRegisterValue(ctx.registers.rdi)
src = ctx.getConcreteRegisterValue(ctx.registers.rsi)
cnt = ctx.getConcreteRegisterValue(ctx.registers.rdx)
for index in range(cnt):
dmem = MemoryAccess(dst + index, 1)
smem = MemoryAccess(src + index, 1)
cell = ctx.getMemoryAst(smem)
expr = ctx.newSymbolicExpression(cell, "strncpy byte")
ctx.setConcreteMemoryValue(dmem, cell.evaluate())
ctx.assignSymbolicExpressionToMemory(expr, dmem)
return dst
def exitHandler(ctx):
debug('[+] exit hooked')
sys.exit(0)
def libcMainHandler(ctx):
debug('[+] __libc_start_main hooked')
# Get arguments
main = ctx.getConcreteRegisterValue(ctx.registers.rdi)
# Push the return value to jump into the main() function
ctx.setConcreteRegisterValue(ctx.registers.rsp, ctx.getConcreteRegisterValue(ctx.registers.rsp)-CPUSIZE.QWORD)
ret2main = MemoryAccess(ctx.getConcreteRegisterValue(ctx.registers.rsp), CPUSIZE.QWORD)
ctx.setConcreteMemoryValue(ret2main, main)
# Setup argc / argv
ctx.concretizeRegister(ctx.registers.rdi)
ctx.concretizeRegister(ctx.registers.rsi)
argvs = [
TARGET, # argv[0]
]
# Define argc / argv
base = BASE_ARGV
addrs = list()
index = 0
for argv in argvs:
addrs.append(base)
ctx.setConcreteMemoryAreaValue(base, bytes(argv.encode('utf8')) + b'\x00')
base += len(argv)+1
debug('[+] argv[%d] = %s' %(index, argv))
index += 1
argc = len(argvs)
argv = base
for addr in addrs:
ctx.setConcreteMemoryValue(MemoryAccess(base, CPUSIZE.QWORD), addr)
base += CPUSIZE.QWORD
ctx.setConcreteRegisterValue(ctx.registers.rdi, argc)
ctx.setConcreteRegisterValue(ctx.registers.rsi, argv)
return 0
# Functions to emulate
customRelocation = [
('__libc_start_main', libcMainHandler, BASE_PLT + 0),
('__isoc99_scanf', scanfHandler, BASE_PLT + 1),
('exit', exitHandler, BASE_PLT + 2),
('printf', printfHandler, BASE_PLT + 3),
('ptrace', ptraceHandler, BASE_PLT + 4),
('putchar', putcharHandler, BASE_PLT + 5),
('puts', putsHandler, BASE_PLT + 6),
('strncpy', strncpyHandler, BASE_PLT + 7),
]
def hookingHandler(ctx):
pc = ctx.getConcreteRegisterValue(ctx.registers.rip)
for rel in customRelocation:
if rel[2] == pc:
# Emulate the routine and the return value
ret_value = rel[1](ctx)
if ret_value is not None:
ctx.setConcreteRegisterValue(ctx.registers.rax, ret_value)
# Get the return address
ret_addr = ctx.getConcreteMemoryValue(MemoryAccess(ctx.getConcreteRegisterValue(ctx.registers.rsp), CPUSIZE.QWORD))
# Hijack RIP to skip the call
ctx.setConcreteRegisterValue(ctx.registers.rip, ret_addr)
# Restore RSP (simulate the ret)
ctx.setConcreteRegisterValue(ctx.registers.rsp, ctx.getConcreteRegisterValue(ctx.registers.rsp)+CPUSIZE.QWORD)
return
def getVarSyntax(ctx):
s = str()
ast = ctx.getAstContext()
for k, v in list(ctx.getSymbolicVariables().items()):
s += str(ast.declare(ast.variable(v))) + '\n'
return s
def getSSA(ctx, expr):
s = str()
ast = ctx.getAstContext()
ssa = ctx.sliceExpressions(expr)
for k, v in sorted(ssa.items())[:-1]:
s += str(v) + '\n'
s += str(ast.assert_(expr.getAst())) + '\n'
return s
# Emulate the binary.
def emulate(ctx, pc):
global SERIAL
global conditions
count = 0
while pc:
# Fetch opcodes
opcodes = ctx.getConcreteMemoryAreaValue(pc, 16)
# Create the Triton instruction
instruction = Instruction()
instruction.setOpcode(opcodes)
instruction.setAddress(pc)
# Process
if ctx.processing(instruction) == EXCEPTION.FAULT_UD:
debug('[-] Instruction not supported: %s' %(str(instruction)))
break
count += 1
#print(instruction)
if instruction.getType() == OPCODE.X86.HLT:
break
# Simulate routines
hookingHandler(ctx)
if pc in conditions:
zf = ctx.getSymbolicRegister(ctx.registers.zf).getAst()
ast = ctx.getAstContext()
pco = ctx.getPathPredicate()
mod = ctx.getModel(zf == 1)
for k, v in list(mod.items()):
ctx.setConcreteVariableValue(ctx.getSymbolicVariable(k), v.getValue())
# End of the execution
if pc == 0x405B00:
debug('[+] Solving the last query to get the good serial...')
ast = ctx.getAstContext()
pco = ctx.getPathPredicate()
mod = ctx.getModel(ast.land(
[pco] +
[ast.variable(ctx.getSymbolicVariable(x)) >= 0x20 for x in range(0, 11)] +
[ast.variable(ctx.getSymbolicVariable(x)) <= 0x7e for x in range(0, 11)] +
[ast.variable(ctx.getSymbolicVariable(x)) != 0x00 for x in range(0, 11)]
))
serial = str()
for k, v in sorted(mod.items()):
serial += chr(v.getValue())
SERIAL = "HACKCON{%s}" %(serial)
print('Serial is: %s' %(SERIAL))
# Next
pc = ctx.getConcreteRegisterValue(ctx.registers.rip)
debug('[+] Instruction executed: %d' %(count))
return
def loadBinary(ctx, binary):
# Map the binary into the memory
phdrs = binary.segments
for phdr in phdrs:
size = phdr.physical_size
vaddr = phdr.virtual_address
debug('[+] Loading 0x%06x - 0x%06x' %(vaddr, vaddr+size))
ctx.setConcreteMemoryAreaValue(vaddr, list(phdr.content))
return
def makeRelocation(ctx, binary):
# Perform our own relocations
try:
for rel in binary.pltgot_relocations:
symbolName = rel.symbol.name
symbolRelo = rel.address
for crel in customRelocation:
if symbolName == crel[0]:
debug('[+] Hooking %s' %(symbolName))
ctx.setConcreteMemoryValue(MemoryAccess(symbolRelo, CPUSIZE.QWORD), crel[2])
except:
pass
# Perform our own relocations
try:
for rel in binary.dynamic_relocations:
symbolName = rel.symbol.name
symbolRelo = rel.address
for crel in customRelocation:
if symbolName == crel[0]:
debug('[+] Hooking %s' %(symbolName))
ctx.setConcreteMemoryValue(MemoryAccess(symbolRelo, CPUSIZE.QWORD), crel[2])
except:
pass
return
def run(ctx, binary):
# Define a fake stack
ctx.setConcreteRegisterValue(ctx.registers.rbp, BASE_STACK)
ctx.setConcreteRegisterValue(ctx.registers.rsp, BASE_STACK)
# Let's emulate the binary from the entry point
debug('[+] Starting emulation.')
emulate(ctx, binary.entrypoint)
debug('[+] Emulation done.')
return
def main():
# Get a Triton context
ctx = TritonContext()
# Set the architecture
ctx.setArchitecture(ARCH.X86_64)
# Set optimization
ctx.setMode(MODE.ALIGNED_MEMORY, True)
ctx.setMode(MODE.ONLY_ON_SYMBOLIZED, True)
ctx.setMode(MODE.CONSTANT_FOLDING, True)
ctx.setMode(MODE.AST_OPTIMIZATIONS, True)
# AST representation as Python syntax
ctx.setAstRepresentationMode(AST_REPRESENTATION.SMT)
# Parse the binary
binary = lief.parse(TARGET)
# Load the binary
loadBinary(ctx, binary)
# Perform our own relocations
makeRelocation(ctx, binary)
# Init and emulate
run(ctx, binary)
return not (SERIAL == 'HACKCON{VVhYS04ngrY}')
if __name__ == '__main__':
retValue = main()
sys.exit(retValue)