Linux Possible GSM Privilege Escalation

SPLUNK detection rule by Raven Tait, Splunk · Apache-2.0

The following analytic detects the commands used in a race condition found in the GSM 0710 tty multiplexor in the Linux kernel. This issue occurs when two threads execute the GSMIOC_SETCONF ioctl on the same tty file descriptor with the gsm line discipline enabled. This could allow a local unprivileged user to escalate their privileges on the system.

name: Linux Possible GSM Privilege Escalation
id: ae13064b-72ea-41fb-9d29-716c27e01208
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 commands used in a race condition found in the GSM 0710 tty multiplexor in the Linux kernel.
    This issue occurs when two threads execute the GSMIOC_SETCONF ioctl on the same tty file descriptor with the gsm line discipline enabled.
    This could allow a local unprivileged user to escalate their privileges on the system.
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="*rmmod *"
    Processes.process="*n_gsm*"
    Processes.process="*exec *"
    Processes.process IN (
        "*/bin/bash*",
        "*/bin/dash*",
        "*/bin/sh*",
        "*/bin/zsh*"
    )

    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_possible_gsm_privilege_escalation_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 testing GSM multiplexor configurations may trigger this detection. Filter based on known authorized users or testing environments.
references:
    - https://access.redhat.com/security/cve/cve-2023-6546
    - https://github.com/Nassim-Asrir/ZDI-24-020/
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 GSM Privilege Escalation via [$process$] by [$user$] on [$dest$].
threat_objects:
    - field: parent_process_name
      type: parent_process_name
    - field: process_name
      type: process_name
    - field: process
      type: process
analytic_story:
    - Linux Privilege Escalation
asset_type: Endpoint
cve:
    - CVE-2023-6546
mitre_attack_id:
    - T1068
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/T1068/linux_possible_linux_gsm_privilege_escalation/snapattack_linux.log
          source: Syslog:Linux-Sysmon/Operational
          sourcetype: sysmon:linux

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