Accéder au contenu principal

Defcon 2015 Coding Skillz 1 Writeup

Par
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()





Related news

Commentaires

Enregistrer un commentaire

Posts les plus consultés de ce blog

The Muse Brooklyn

Par
http://abcirque.com http://www.amny.com/things-to-do/circus-class-at-the-muse-brooklyn-teaches-acrobatic-skills-1.13781898 https://www.instagram.com/p/Bx-D67pAxGz/ https://www.instagram.com/p/Bx7e3GFgpp2/ https://www.instagram.com/p/Bx5xpoPn_hm/ https://www.instagram.com/p/Bx40FSvj2Tf/ https://www.instagram.com/p/Bx0p224DkxE/ https://www.instagram.com/p/BxzxjhqFO1S/ https://www.instagram.com/p/BxyJmIaAeSd/ https://www.instagram.com/p/BxxweSaF6q4/ https://www.instagram.com/p/BxxSsdcAjFg/ https://www.instagram.com/p/Bxvr0SSgpPs/ https://new.mta.info/L-Project http://themusegowanus.com http://instagram.com/themusebrooklyn https://www.facebook.com/TheMuseBrooklyn/ https://twitter.com/TheMuseBrooklyn https://www.youtube.com/channel/UCkzh62AIfOI7XU3I0P6rWIQ
Enregistrer un commentaire
Lire la suite

Fw:

Par
Consider this message as your last warning. We hacked your system! We have copied all the data from your device to our own servers. Curious videos were recorded from your camera and your actions while watching porn. Your device was infected with our virus when you visited the porn site. The Trojan virus gives us full access, allows us to control your device. The virus allows not only to see your screen, but also to turn on your camera, microphone, without your knowledge. We took over the video from your screen and camera, then we mounted a video in which you can see you watching porn in one part of the screen and masturbating in the other. But that’s not all! We have access to all the contacts in your phone book and social networks. It won’t take us long to send this video to your friends, family and friends on social networks, messengers and email in minutes. We have a lot of audio recordings of your personal conversations, where a lot of “intere...
Enregistrer un commentaire
Lire la suite

Systemic Lidocaine Decreased the Perioperative Opioid Analgesic Requirements but Failed to Reduce Discharge Time After Ambulatory Surgery

Par
Perioperative systemic lidocaine significantly reduces opioid requirements in the ambulatory setting without affecting time to discharge. Postoperative pain is the most common reason for delay in discharge and unplanned hospital admission after ambulatory surgery. 1–3 Because postoperative pain is to a large extent an inflammatory phenomenon, administration of systemic local anesthetics, which have inflammatory modulatory properties, 4 could significantly reduce pain and therefore allow more rapid discharge. 5 Lidocaine has an excellent safety record when administered by low-dose infusion. 5–7 However, whereas decreased hospital stay after inpatient surgery has been demonstrated, the effect of intraoperative and early postoperative lidocaine infusion on duration of stay after ambulatory surgery is not known. Although it see...
Enregistrer un commentaire
Lire la suite