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Socket Filters (T1205.002) is a MITRE ATT&CK technique associated with Stealth, Persistence, Command and Control . Adversaries may attach filters to a network socket to monitor then activate backdoors used for persistence or command and control.
Socket Filters (T1205.002) is a MITRE ATT&CK technique associated with Stealth, Persistence, Command and Control. Adversaries may attach filters to a network socket to monitor then activate backdoors used for persistence or command and control.
Attackers use Socket Filters because it provides a reliable way to advance their objective within the Stealth, Persistence, Command and Control tactic, often with a favorable balance of impact versus detectability on Linux, macOS, Windows environments. Defenders should assess this behavior in the context of the affected platform and adjacent activity rather than treating it as a standalone indicator.
Adversaries may attach filters to a network socket to monitor then activate backdoors used for persistence or command and control. With elevated permissions, adversaries can use features such as the libpcap library to open sockets and install filters to allow or disallow certain types of data to come through the socket. The filter may apply to all traffic passing through the specified network interface (or every interface if not specified). When the network interface receives a packet matching the filter criteria, additional actions can be triggered on the host, such as activation of a reverse shell.
To establish a connection, an adversary sends a crafted packet to the targeted host that matches the installed filter criteria.(Citation: haking9 libpcap network sniffing) Adversaries have used these socket filters to trigger the installation of implants, conduct ping backs, and to invoke command shells. Communication with these socket filters may also be used in conjunction with Protocol Tunneling.(Citation: exatrack bpf filters passive backdoors)(Citation: Leonardo Turla Penquin May 2020)
Filters can be installed on any Unix-like platform with libpcap installed or on Windows hosts using Winpcap. Adversaries may use either libpcap with pcap_setfilter or the standard library function setsockopt with SO_ATTACH_FILTER options. Since the socket connection is not active until the packet is received, this behavior may be difficult to detect due to the lack of activity on a host, low CPU overhead, and limited visibility into raw socket usage.
No universal command represents Socket Filters. Capture the exact command line, arguments, parent process, account, host, and execution time from the investigated environment; do not operationalize unverified examples.
| Event ID | Log Channel | What It Indicates |
|---|---|---|
| Environment-specific | Relevant Windows channel(s) | Correlate authentication, process, object-access, and configuration events with the observed execution context. |
| Sysmon Event ID | Name | Why It's Relevant Here |
|---|---|---|
| Environment-specific | Validate configured telemetry | Use process, network, file, registry, DNS, or image-load telemetry only when relevant and enabled. |
No MITRE detection guidance published for this technique.
Relevant ATT&CK Data Sources: N/A
A universal Sigma rule would create unreliable results because this technique has no single guaranteed observable. Build detection logic from a documented behavior and supported data source, scope it to the affected platform, and validate it against benign administrative activity before deployment.
Start with the data sources named in the detection section. Scope searches by asset, identity, and time window; correlate the primary behavior with preceding access and subsequent actions. A portable query is intentionally not provided where the technique lacks a universal schema or observable.