Single Letter Process On Endpoint

name: Single Letter Process On Endpoint
id: a4214f0b-e01c-41bc-8cc4-d2b71e3056b4
version: 14
creation_date: '2020-04-29'
modification_date: '2026-05-13'
author: David Dorsey, Splunk
status: production
type: TTP
description: The following analytic detects processes with names consisting of a single letter, which is often indicative of malware or an attacker attempting to evade detection. This detection leverages data from Endpoint Detection and Response (EDR) agents, focusing on process names and command-line executions. This activity is significant because attackers use such techniques to obscure their presence and carry out malicious activities like data theft or ransomware attacks. If confirmed malicious, this behavior could lead to unauthorized access, data exfiltration, or system compromise. Immediate investigation is required to determine the legitimacy of the process.
data_source:
    - Sysmon EventID 1
    - Windows Event Log Security 4688
    - CrowdStrike ProcessRollup2
search: |
    | tstats `security_content_summariesonly`
      count min(_time) as firstTime
            max(_time) as lastTime
      from datamodel=Endpoint.Processes where
      Processes.process_name IN (
        "_.exe",
        "-.exe",
        ",.exe",
        ";.exe",
        "!.exe",
        "'.exe"
        "(.exe",
        "(.exe",
        ").exe",
        ").exe",
        "@.exe",
        "&.exe",
        "#.exe",
        "%.exe",
        "`.exe",
        "^.exe",
        "+.exe",
        "=.exe",
        "~.exe",
        "$.exe",
        "0.exe",
        "1.exe",
        "2.exe",
        "3.exe",
        "4.exe",
        "5.exe",
        "6.exe",
        "7.exe",
        "8.exe",
        "9.exe",
        "a.exe",
        "b.exe",
        "c.exe",
        "d.exe",
        "e.exe",
        "f.exe",
        "g.exe",
        "h.exe",
        "i.exe",
        "j.exe",
        "k.exe",
        "l.exe",
        "m.exe",
        "N.exe",
        "o.exe",
        "p.exe",
        "q.exe",
        "r.exe",
        "s.exe",
        "t.exe",
        "u.exe",
        "v.exe",
        "w.exe",
        "x.exe",
        "y.exe",
        "z.exe",
      )
    by Processes.action Processes.dest Processes.original_file_name Processes.parent_process
       Processes.parent_process_exec Processes.parent_process_guid Processes.parent_process_id
       Processes.parent_process_name Processes.parent_process_path Processes.process
       Processes.process_exec Processes.process_guid Processes.process_hash Processes.process_id
       Processes.process_integrity_level Processes.process_name Processes.process_path Processes.user
       Processes.user_id Processes.vendor_product
    | `drop_dm_object_name(Processes)`
    | `security_content_ctime(lastTime)`
    | `security_content_ctime(firstTime)`
    | `single_letter_process_on_endpoint_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: Single-letter executables are not always malicious. Investigate this activity with your normal incident-response process.
references: []
drilldown_searches:
    - name: View the detection results for - "$dest$" and "$user$"
      search: '%original_detection_search% | search  dest = "$dest$" user = "$user$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$dest$" and "$user$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$dest$", "$user$") | 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"
finding:
    title: A suspicious process $process_name$ with single letter on host $dest$
    entity:
        field: user
        type: user
        score: 50
intermediate_findings:
    entities:
        - field: dest
          type: system
          score: 50
          message: A suspicious process $process_name$ with single letter on host $dest$
analytic_story:
    - DHS Report TA18-074A
    - Compromised Windows Host
asset_type: Endpoint
mitre_attack_id:
    - T1204.002
product:
    - Splunk Enterprise
    - Splunk Enterprise Security
    - Splunk Cloud
category: endpoint
security_domain: endpoint
tests:
    - name: True Positive Test
      attack_data:
        - data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1204.002/single_letter_exe/windows-sysmon.log
          source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
          sourcetype: XmlWinEventLog
      test_type: unit