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DefCon CtF Quals 2014 writeup – hackertool

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hey, we need to check that your connection works, torrent this file and md5 it

http://services.2014.shallweplayaga.me/hackertool.torrent_fe3b8b75e9639d35e8ac1d9809726ee2

The torrent file when loaded into Vuze showed that the file name was every_ip_address.txt. So I downloaded some of the file and observed the format. The format of the file was “0.0.0.1\n0.0.0.2\n…. “.

So I wrote a quick python script to calculate the md5:

#!/bin/python
import hashlib
m = hashlib.md5()
fsize = 0
a = ''
for i in xrange(256):
    for j in xrange(256):
        for k in xrange(256):
            for l in xrange(256):
                a = str(i)+'.'+str(j)+'.'+str(k)+'.'+str(l)+'\n'
                fsize += len(a)
                m.update( a )
print m.hexdigest()

The flag was “1a97f624cc74e4944350c04f5ae1fe8d”.

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Cisco IPSec VPN Client Reason442: Failed to Enable Virtual Adapter

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If you use Windows 8 x64 and when you launch the Cisco VPN Client adapter and you see the following error:
Reason 442: Failed To Enable Virtual Adapter Here’s how to fix it.
Open your command prompt in Administrator mode by right clicking at the left lower corner of the screen and going to “Command Prompt (Administrator)”. You will have to log in as an administrator. Launch registry editor by typing “regedit.exe”. Browse to “HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\CVirtA“. In the DisplayName key, you will see something like @oem8.inf,%CVirtA_Desc%;Cisco Systems VPN Adapter. Edit that to just say Cisco Systems VPN Adapter. Try to connect again by launching the VPN Client. It should work!

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PlaidCTF 2013 – Crypto 250 Compression Writeup

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On the recently concluded PlaidCTF (which was an awesome competition) by PPP there was a problem.  Here it goes:

Question: We managed to get the source code for an encryption service running at 54.234.224.216:4433.

I have listed the python source provided below:

#!/usr/bin/python
import os
import struct
import SocketServer
import zlib
from Crypto.Cipher import AES
from Crypto.Util import Counter

# Not the real keys!
ENCRYPT_KEY = '0000000000000000000000000000000000000000000000000000000000000000'.decode('hex')
# Determine this key.
# Character set: lowercase letters and underscore
PROBLEM_KEY = 'XXXXXXXXXXXXXXXXXXXX'

def encrypt(data, ctr):
    aes = AES.new(ENCRYPT_KEY, AES.MODE_CTR, counter=ctr)
    return aes.encrypt(zlib.compress(data))

class ProblemHandler(SocketServer.StreamRequestHandler):
    def handle(self):
        nonce = os.urandom(8)
        self.wfile.write(nonce)
        ctr = Counter.new(64, prefix=nonce)
        while True:
            data = self.rfile.read(4)
            if not data:
                break

            try:
                length = struct.unpack('I', data)[0]
                if length > (1<<20):
                    break
                data = self.rfile.read(length)
                data += PROBLEM_KEY
                ciphertext = encrypt(data, ctr)
                self.wfile.write(struct.pack('I', len(ciphertext)))
                self.wfile.write(ciphertext)
            except:
                break

class ReusableTCPServer(SocketServer.ForkingMixIn, SocketServer.TCPServer):
    allow_reuse_address = True

if __name__ == '__main__':
    HOST = '0.0.0.0'
    PORT = 4433
    SocketServer.TCPServer.allow_reuse_address = True
    server = ReusableTCPServer((HOST, PORT), ProblemHandler)
    server.serve_forever()

The key on this challenge is to see that the stream encryption is being done on the compressed input. In the source provided, if the user input is similar to the secret value in the PROBLEM_DATA variable then the zlib.compress() function would show a reduced length ciphertext. This is somewhat (and I use the term loosely) similar to the CRIME vulnerability. The AES Counter mode RFC has the implementation details of the cipher. So I wrote the following script.

import socket
import sys
from itertools import *
import struct
def display(msg,numbytes):
	#print >>sys.stderr, 'received "%s"' % msg
	#print >>sys.stderr, 'bytes "%d"' % numbytes
	print >>sys.stderr, 'bytes %d ' % numbytes + msg.encode('hex')
# Create a TCP/IP socket
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
# Connect the socket to the port where the server is listening
server_address = ('54.234.224.216', 4433)
print >>sys.stderr, 'connecting to %s port %s' % server_address
sock.connect(server_address)
#mesage len = 20 lowercase and underscore letters
try:
	amount_received = 0
	nonce = sock.recv(8)
	amount_received += len(nonce)
	# Send data
	#strng = 'crime_some'
	#minciphlen = 1000
	#strng = 'crimes_pays'
	#strng = 'so_'
	#strng = 'crime_some_times_pays'
	#strng = 'somet_'
	strng = 'cr'
	minchar = ''
	ciphlen = 1000
	sampleset = 'hijklmnopqrstuvwxyz_abdefgc'
	#while True:
	strng = strng + minchar	
	minciphlen = ciphlen
	minchar = ''
	for s in map("".join,permutations(sampleset,1)):
		#message = nonce +  (strng + s)*10  #'\x00'*11 + s
		message = strng + s
		datalen = struct.pack('I',len(message))  # datalen = '\xe4\x00\x00\x00'
		sock.sendall(datalen)
		#print >>sys.stderr, 'sending '+ message
		sock.sendall(message)
		#print >>sys.stderr, 'message sent'
		amount_received = 0
		# Look for the response
		data = sock.recv(4)
		amount_received += len(data)
		ciphlen = struct.unpack('I', data)[0]
		#print >>sys.stderr, message + ' ' 
		amount_received = 0
		if ciphlen <= minciphlen:
			minciphlen = ciphlen
			minchar = s
			print str(ciphlen) + ' It is ' + strng + minchar
		data = sock.recv(ciphlen)
		#display(data,ciphlen)		
finally:
    print >>sys.stderr, 'closing socket'
    sock.close()

When you connect to the service it provides you the nonce, so I prepended the nonce to the plaintext. The above script shows the plaintext and the length of the cipher text. To start off with this, you start with a string of length 1, and see which is the smallest length response, that gives your first character. Then in the

strng

variable above, you add that character and run again, and the lowest length ciphertext tells you the next character and so on. I noticed that sometimes the output had a few characters with the lowest length. So I tried each of them and ended up with the following flag:

crime_sometimes_pays 
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Verizon FiOS and PS3 Media Server Streaming Issues

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If you’re like me and recently upgraded to Verizon FiOS and you have your PS3 on the wired segment and the Media Server (such as PS3 Media Server, TVersity, etc.) on the wireless segment, you’re in for a ride with the configuration.
By default, you can’t route the traffic between the wired and wireless segments over UDP! You can send ICMP echo packets (i.e., ping) but the PS3 just won’t detect the Media server. You may disable the Host-based firewall (e.g., Norton, Kaspersky, McAfee, etc.) but it still won’t work.

If you happen to read posts like these, you will see that you have to disable “IGMP proxy”. IGMP Proxy basically reduces the traffic on the multicast addresses to a bare minimum. Unfortunately for you, this causes the traffic between PS3 Media Server and PS3 to drop.

So you log into your FiOS router’s administration console typically located at 192.168.1.1. Click on Advanced -> Yes -> Firmware Upgrade and check the firmware version. You will see that it is an ActionTec router (based on the Auto-update URL). But nowhere do you see the option to update the “IGMP Proxy” settings. That’s because that feature is “hidden” in the latest firmwares.

So you just need to copy/paste the following URL into the browser address bar and you will see the option to disable “IGMP proxy”.
http://192.168.1.1/index.cgi?active_page=6059
Disable it and Voila! The PS3 Media Server and PS3 can now talk to each other.

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Socat compilation on Cygwin

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While compiling socat-2.0.0-b5 on cygwin (Windows) I got a few errors and here’s how I fixed it:
xioopts.c: In function 'applyopts_single':
xioopts.c:3998: error: 'struct single' has no member named 'fd1'
xioopts.c:4000: error: 'struct single' has no member named 'fd1'
make[1]: *** [xioopts.o] Error 1

Edit the file xioopts.c in your favorite editor and replace ‘fd1’ by ‘rfd’ in both lines (3998 & 4000). That fixed this error but then I got my next error.

xio-ip.c:480: error: structure has no member named `ipi_spec_dst'
Edit xio-ip.c and comment out the entire snprintf statement in xio-ip.c line 480.

Continue compilation and it should now work fine.