Linux Shell Pseudo Device Reverse Shell

name: Linux Shell Pseudo Device Reverse Shell
id: f324bc06-8436-4606-8882-0a8fb480b719
version: 1
creation_date: '2026-07-08'
modification_date: '2026-07-08'
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/*"
    )

    by Processes.process Processes.vendor_product
       Processes.user_id Processes.process_hash Processes.parent_process_name Processes.parent_process_exec
       Processes.action Processes.dest Processes.process_current_directory Processes.process_path
       Processes.process_integrity_level Processes.original_file_name Processes.parent_process
       Processes.parent_process_path Processes.parent_process_guid Processes.parent_process_id
       Processes.process_guid Processes.process_id Processes.user Processes.process_name

    | `drop_dm_object_name(Processes)`
    | `security_content_ctime(firstTime)`
    | `security_content_ctime(lastTime)`
    |`linux_shell_pseudo_device_reverse_shell_filter`
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'
intermediate_findings:
    entities:
        - field: dest
          type: system
          score: 20
          message: Potential reverse shell [$process$] by [$user$] on [$dest$] via [$process_name$].
        - field: user
          type: user
          score: 20
          message: Potential reverse shell [$process$] by [$user$] on [$dest$] via [$process_name$].
threat_objects:
    - field: parent_process_name
      type: parent_process_name
    - field: process_name
      type: process_name
analytic_story:
    - Linux Post-Exploitation
    - Linux Persistence Techniques
    - Linux Privilege Escalation
    - Command And Control
    - Compromised Linux Host
asset_type: Endpoint
mitre_attack_id:
    - T1059
    - T1048.003
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: endpoint
security_domain: endpoint
tests:
    - name: True Positive Test
      test_type: unit
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1059/linux_bash_reverse_shell/snapattack_linux.log
          source: Syslog:Linux-Sysmon/Operational
          sourcetype: sysmon:linux