Windows Alternate DataStream - Executable Content

Description

The following analytic detects the writing of data with an IMPHASH value to an Alternate Data Stream (ADS) in the NTFS file system. It leverages Sysmon Event ID 15 and regex to identify files with a Portable Executable (PE) structure. This activity is significant as it may indicate a threat actor staging malicious code in hidden areas for persistence or future execution. If confirmed malicious, this could allow attackers to execute hidden code, maintain persistence, or escalate privileges within the environment.

Query · spl

`sysmon` EventCode=15 IMPHASH!=00000000000000000000000000000000 | regex TargetFilename="(?<!\/)\b\w+(\.\w+)?:\w+(\.\w+)?$" | eval file_name = replace(TargetFilename,"(.*\\\)",""), process = Image , file_path = TargetFilename, file_hash = coalesce(SHA256,SHA1,MD5,Hash) | stats count min(_time) as firstTime max(_time) as lastTime by dest dvc file_hash file_name file_path process_exec process_guid process_id process_name process_path signature signature_id user_id vendor_product Contents Image | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `windows_alternate_datastream___executable_content_filter`

Implementation guide

Target environment must ingest Sysmon data, specifically Event ID 15, and import hashing/imphash must be enabled within Sysmon.

Known false positives

  • No false positives have been identified at this time.

Analyst notes

Known false positives: No false positives have been identified at this time.

Raw source Windows Alternate DataStream - Executable Content · SPL
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Published by splunk/security_content ↗, licensed under Apache 2.0 ↗. Reproduced here unmodified. 
name: Windows Alternate DataStream - Executable Content
id: a258bf2a-34fd-4986-8086-78f506e00206
version: 13
creation_date: '2024-01-10'
modification_date: '2026-05-13'
author: Steven Dick, Teoderick Contreras, Splunk
status: production
type: TTP
description: The following analytic detects the writing of data with an IMPHASH value to an Alternate Data Stream (ADS) in the NTFS file system. It leverages Sysmon Event ID 15 and regex to identify files with a Portable Executable (PE) structure. This activity is significant as it may indicate a threat actor staging malicious code in hidden areas for persistence or future execution. If confirmed malicious, this could allow attackers to execute hidden code, maintain persistence, or escalate privileges within the environment.
data_source:
    - Sysmon EventID 15
search: '`sysmon` EventCode=15 IMPHASH!=00000000000000000000000000000000 | regex TargetFilename="(?<!\/)\b\w+(\.\w+)?:\w+(\.\w+)?$" | eval file_name = replace(TargetFilename,"(.*\\\)",""), process = Image , file_path = TargetFilename, file_hash = coalesce(SHA256,SHA1,MD5,Hash) | stats count min(_time) as firstTime max(_time) as lastTime by dest dvc file_hash file_name file_path process_exec process_guid process_id process_name process_path signature signature_id user_id vendor_product Contents Image | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)` | `windows_alternate_datastream___executable_content_filter`'
how_to_implement: Target environment must ingest Sysmon data, specifically Event ID 15, and import hashing/imphash must be enabled within Sysmon.
known_false_positives: No false positives have been identified at this time.
references:
    - https://car.mitre.org/analytics/CAR-2020-08-001/
    - https://blogs.juniper.net/en-us/threat-research/bitpaymer-ransomware-hides-behind-windows-alternate-data-streams
    - https://twitter.com/0xrawsec/status/1002478725605273600?s=21
drilldown_searches:
    - name: View the detection results for - "$dest$"
      search: '%original_detection_search% | search  dest = "$dest$"'
      earliest_offset: $info_min_time$
      latest_offset: $info_max_time$
    - name: View risk events for the last 7 days for - "$dest$"
      search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$dest$") | 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"
finding:
    title: Base64 content written to an NTFS alternate data stream in $dest$, see command field for details.
    entity:
        field: dest
        type: system
        score: 50
threat_objects:
    - field: file_hash
      type: file_hash
    - field: file_name
      type: file_name
analytic_story:
    - Windows Defense Evasion Tactics
asset_type: Endpoint
mitre_attack_id:
    - T1564.004
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/T1564.004/ads_abuse/ads_abuse_sysmon.log
          source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
          sourcetype: XmlWinEventLog
      test_type: unit

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