Network Sniffing

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Network Sniffing
ID T842
Tactic Discovery
Data Sources Network device logs, Host network interfaces, Process monitoring, Netflow/Enclave netflow
Asset Field Controller/RTU/PLC/IED


Network sniffing is the practice of using a network interface on a computer system to monitor or capture information1 regardless of whether it is the specified destination for the information.

An adversary may attempt to sniff the traffic to gain information about the target. This information can vary in the level of importance. Relatively unimportant information is general communications to and from machines. Relatively important information would be login information. User credentials may be sent over an unencrypted protocol, such as Telnet, that can be captured and obtained through network packet analysis. Network sniffing can be a way to discover information for Control Device Identification.

In addition, ARP and Domain Name Service (DNS) poisoning can be used to capture credentials to websites, proxies, and internal systems by redirecting traffic to an adversary.

Procedure Examples

  • DP_RECV is the name of a standard function block used by network coprocessors. It is used to receive network frames on the Profibus – a standard industrial network bus used for distributed I/O. The original block is copied to FC1869, and then replaced by a malicious block. Each time the function is used to receive a packet, the malicious Stuxnet block takes control: it will call the original DP_RECV in FC1869 and then perform postprocessing on the packet data. This secondary thread is used to monitor a data block DB890 of sequence A or B. Though constantly running and probing this block (every 5 minutes), this thread has no purpose if the PLC is not infected. The purpose of the thread is to monitor each S7-315 on the bus. The replaced DP_RECV block (later on referred to as the “DP_RECV monitor”) is meant to monitor data sent by the frequency converter drives to the 315-2 CPU via CP 342-5 Profibus communication modules.2
  • The VPNFilter packet sniffer looks for basic authentication as well as monitors ICS traffic, and is specific to the TP-LINK R600-VPN. The malware uses a raw socket to look for connections to a pre-specified IP address, only looking at TCP packets that are 150 bytes or larger. Packets that are not on port 502, are scanned for BasicAuth, and that information is logged. This may have allowed credential harvesting from communications between devices accessing a modbus-enabled HMI.34


  • Prior to wireless network installation, survey the area to determine the antenna location and strength that minimizes exposure of the network. An adversary is capable of extending the effective range of a wireless LAN with powerful directional antennas.5
  • Isolate wireless access points and data servers for wireless worker devices on their own network with documented and minimal (single if possible) connections to the ICS network.5
  • Segmenting the network with VLANs allow switches to enforce security policies and segregate traffic at the Ethernet layer. Proper segmentation helps mitigate the risk of broadcast storms resulting from port scans. Assigning each automation cell to a single VLAN limits unnecessary traffic flooding.5
  • Implement VPNs to further restrict access in and out of control system computers and controllers, which help remove unauthorized, non-essential traffic from the intermediary network.5
  • In ICS environments with dial-up modems, disconnect the modems when not in use or automate their disconnection after being active for a given amount of time, if reasonable.5
  • Network services will often transmit in plaintext, making third-party eavesdropping easy. When communications over both encrypted and non-encrypted protocols with passwords exist, be sure to use different passwords.5
  • Implementing Challenge/Response authentication eliminates the risk of discovery or replay that traditional password exchange has.5
  • Secure and restrict authorization to the control room and the physical environment. Ensure ICS and IT network cables are kept separate and that devices are locked up when possible.5
  • Encrypt and protect the integrity of wireless device communications, while taking care not to degrade end device performance. OSI Layer 2 encryption, rather than Layer 3, can reduce encryption-based latency. Hardware accelerator solutions for cryptographic functions may also be considered.5
  • Ensure that all wireless traffic is encrypted appropriately. Use Kerberos, SSL, and multifactor authentication wherever possible. Monitor switches and network for span port usage, ARP/DNS poisoning, and router reconfiguration.5
  • Make use of antivirus and malware detection tools to further secure the environment. Monitor the network and enforce access control practices, such as whitelisting, to reduce points of contact to and from control system devices, where applicable. Implement heuristics to detect monitoring and invasive probing activity on the network.5
  • Identify and block potentially malicious software that may be used to sniff or analyze network traffic by using whitelisting6 tools, like AppLocker,78 or Software Restriction Policies9 where appropriate.10