Name:Linux Shell Pseudo Device Reverse Shell id:f324bc06-8436-4606-8882-0a8fb480b719 version:1 date:None author:Raven Tait, Splunk status:production type:Anomaly Description:The following analytic detects the use of shell's /dev/tcp or /dev/udp pseudo-device feature to establish outbound network connections.
This special file system interface allows opening a network socket and sending or receiving data using simple shell commands.
Attackers commonly abuse this native shell capability to create reverse shells without requiring external tools such as netcat, by redirecting shell I/O over a TCP or UDP connection to an attacker-controlled host and port. Data_source:
-Sysmon for Linux EventID 1
search:| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime
from datamodel=Endpoint.Processes where
Processes.process_name IN ( "bash", "dash", "sh", "zsh" ) Processes.process IN ( "*/dev/tcp/*", "*/dev/udp/*" )
how_to_implement:The detection is based on data that originates from Endpoint Detection and Response (EDR) agents. These agents are designed to provide security-related telemetry from the endpoints where the agent is installed. To implement this search, you must ingest logs that contain the process GUID, process name, and parent process. Additionally, you must ingest complete command-line executions. These logs must be processed using the appropriate Splunk Technology Add-ons that are specific to the EDR product. The logs must also be mapped to the `Processes` node of the `Endpoint` data model. Use the Splunk Common Information Model (CIM) to normalize the field names and speed up the data modeling process. known_false_positives:Legitimate system administrators or developers may use /dev/tcp or /dev/udp for network diagnostics or testing purposes.
Filter based on known authorized users and trusted source systems. References: -https://swisskyrepo.github.io/InternalAllTheThings/cheatsheets/shell-reverse-cheatsheet/#bash-tcp drilldown_searches: earliest_offset:'$info_min_time$' latest_offset:'$info_max_time$' name:'View the detection results for - "$user$" and "$dest$"' search:'%original_detection_search% | search user = "$user$" dest = "$dest$"' name:'View risk events for the last 7 days for - "$user$" and "$dest$"' search:'| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$user$", "$dest$") | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`' earliest_offset:'7d' latest_offset:'0' analytic_story:['Linux Post-Exploitation', 'Linux Persistence Techniques', 'Linux Privilege Escalation', 'Command And Control', 'Compromised Linux Host']
