Network sniffing refers to using the network interface on a system to monitor or capture information sent over a wired or wireless connection. An adversary may place a network interface into promiscuous mode to passively access data in transit over the network, or use span ports to capture a larger amount of data.
Data captured via this technique may include user credentials, especially those sent over an insecure, unencrypted protocol. Techniques for name service resolution poisoning, such as LLMNR/NBT-NS Poisoning and Relay, can also be used to capture credentials to websites, proxies, and internal systems by redirecting traffic to an adversary.
Network sniffing may also reveal configuration details, such as running services, version numbers, and other network characteristics (ex: IP addressing, hostnames, VLAN IDs) necessary for follow-on Lateral Movement and/or Defense Evasion activities.
|APT28||APT28 deployed the open source tool Responder to conduct NetBIOS Name Service poisoning, which captured usernames and hashed passwords that allowed access to legitimate credentials.  |
|APT33||APT33 has used SniffPass to collect credentials by sniffing network traffic. |
|Emotet||Emotet has been observed to hook network APIs to monitor network traffic. |
|Empire||Empire can be used to conduct packet captures on target hosts. |
|Impacket||Impacket can be used to sniff network traffic via an interface or raw socket. |
|PoshC2||PoshC2 contains a module for taking packet captures on compromised hosts. |
|Regin||Regin appears to have functionality to sniff for credentials passed over HTTP, SMTP, and SMB. |
|Responder||Responder captures hashes and credentials that are sent to the system after the name services have been poisoned. |
|Stolen Pencil||Stolen Pencil has a tool to sniff the network for passwords. |
|Encrypt Sensitive Information||Ensure that all wired and/or wireless traffic is encrypted appropriately. Use best practices for authentication protocols, such as Kerberos, and ensure web traffic that may contain credentials is protected by SSL/TLS.|
|Multi-factor Authentication||Use multi-factor authentication wherever possible.|
Detecting the events leading up to sniffing network traffic may be the best method of detection. From the host level, an adversary would likely need to perform a man-in-the-middle attack against other devices on a wired network in order to capture traffic that was not to or from the current compromised system. This change in the flow of information is detectable at the enclave network level. Monitor for ARP spoofing and gratuitous ARP broadcasts. Detecting compromised network devices is a bit more challenging. Auditing administrator logins, configuration changes, and device images is required to detect malicious changes.
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