Defcon 2015 Coding Skillz 1 Writeup

Just connecting to the service, a 64bit cpu registers dump is received, and so does several binary code as you can see:

The registers represent an initial cpu state, and we have to reply with the registers result of the binary code execution. This must be automated becouse of the 10 seconds server socket timeout.

The exploit is quite simple, we have to set the cpu registers to this values, execute the code and get resulting registers.

In python we created two structures for the initial state and the ending state.

cpuRegs = {'rax':'','rbx':'','rcx':'','rdx':'','rsi':'','rdi':'','r8':'','r9':'','r10':'','r11':'','r12':'','r13':'','r14':'','r15':''}
finalRegs = {'rax':'','rbx':'','rcx':'','rdx':'','rsi':'','rdi':'','r8':'','r9':'','r10':'','r11':'','r12':'','r13':'','r14':'','r15':''}

We inject at the beginning several movs for setting the initial state:

for r in cpuRegs.keys():

    code.append('mov %s, %s' % (r, cpuRegs[r]))

The 64bit compilation of the movs and the binary code, but changing the last ret instruction by a sigtrap "int 3"

We compile with nasm in this way:

os.popen('nasm -f elf64 code.asm')

os.popen('ld -o code code.o ')

And use GDB to execute the code until the sigtrap, and then get the registers

fd = os.popen("gdb code -ex 'r' -ex 'i r' -ex 'quit'",'r')

for l in fd.readlines():

    for x in finalRegs.keys():

           ...

We just parse the registers and send the to the server in the same format, and got the key.

The code:

from libcookie import *

from asm import *

import os

import sys

host = 'catwestern_631d7907670909fc4df2defc13f2057c.quals.shallweplayaga.me'

port = 9999

cpuRegs = {'rax':'','rbx':'','rcx':'','rdx':'','rsi':'','rdi':'','r8':'','r9':'','r10':'','r11':'','r12':'','r13':'','r14':'','r15':''}

finalRegs = {'rax':'','rbx':'','rcx':'','rdx':'','rsi':'','rdi':'','r8':'','r9':'','r10':'','r11':'','r12':'','r13':'','r14':'','r15':''}

fregs = 15

s = Sock(TCP)

s.timeout = 999

s.connect(host,port)

data = s.readUntil('bytes:')

#data = s.read(sz)

#data = s.readAll()

sz = 0

for r in data.split('\n'):

    for rk in cpuRegs.keys():

        if r.startswith(rk):

            cpuRegs[rk] = r.split('=')[1]

    if 'bytes' in r:

        sz = int(r.split(' ')[3])

binary = data[-sz:]

code = []

print '[',binary,']'

print 'given size:',sz,'bin size:',len(binary)        

print cpuRegs

for r in cpuRegs.keys():

    code.append('mov %s, %s' % (r, cpuRegs[r]))

#print code

fd = open('code.asm','w')

fd.write('\n'.join(code)+'\n')

fd.close()

Capstone().dump('x86','64',binary,'code.asm')

print 'Compilando ...'

os.popen('nasm -f elf64 code.asm')

os.popen('ld -o code code.o ')

print 'Ejecutando ...'

fd = os.popen("gdb code -ex 'r' -ex 'i r' -ex 'quit'",'r')

for l in fd.readlines():

    for x in finalRegs.keys():

        if x in l:

            l = l.replace('\t',' ')

            try:

                i = 12

                spl = l.split(' ')

                if spl[i] == '':

                    i+=1

                print 'reg: ',x

                finalRegs[x] = l.split(' ')[i].split('\t')[0]

            except:

                print 'err: '+l

            fregs -= 1

            if fregs == 0:

                #print 'sending regs ...'

                #print finalRegs

                

                buff = []

                for k in finalRegs.keys():

                    buff.append('%s=%s' % (k,finalRegs[k]))

                print '\n'.join(buff)+'\n'

                print s.readAll()

                s.write('\n'.join(buff)+'\n\n\n')

                print 'waiting flag ....'

                print s.readAll()

                print '----- yeah? -----'

                s.close()

                

fd.close()

s.close()

More info

1. Hack Tools Github
2. Hacking Tools Github
3. Pentest Tools
4. Hacks And Tools
5. Hack Tools
6. Termux Hacking Tools 2019
7. Hacker Tools Online
8. Physical Pentest Tools
9. Pentest Tools Nmap
10. Hacking Tools 2019
11. Tools For Hacker
12. Hacking Tools For Beginners
13. Pentest Tools Download
14. Bluetooth Hacking Tools Kali
15. Hack Website Online Tool
16. Pentest Tools List
17. Hacking Tools And Software
18. Hacking Tools Download
19. Hack Tool Apk No Root
20. Hack Tools Mac
21. Hacking Tools And Software
22. Computer Hacker
23. Hack Tool Apk No Root
24. Pentest Tools Nmap
25. Hack App
26. Pentest Box Tools Download
27. Hack Website Online Tool
28. Hackers Toolbox
29. Hacker Tools For Pc