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Eric
78 lines
3.6 KiB
YAML
78 lines
3.6 KiB
YAML
name: PowerShell WebRequest Using Memory Stream
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id: 103affa6-924a-4b53-aff4-1d5075342aab
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version: 6
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date: '2025-05-02'
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author: Steven Dick
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status: production
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type: TTP
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description: The following analytic detects the use of .NET classes in PowerShell
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to download a URL payload directly into memory, a common fileless malware staging
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technique. It leverages PowerShell Script Block Logging (EventCode=4104) to identify
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suspicious PowerShell commands involving `system.net.webclient`, `system.net.webrequest`,
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and `IO.MemoryStream`. This activity is significant as it indicates potential fileless
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malware execution, which is harder to detect and can bypass traditional file-based
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defenses. If confirmed malicious, this technique could allow attackers to execute
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code in memory, evade detection, and maintain persistence in the environment.
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data_source:
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- Powershell Script Block Logging 4104
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search: '`powershell` EventCode=4104 ScriptBlockText IN ("*system.net.webclient*","*system.net.webrequest*")
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AND ScriptBlockText="*IO.MemoryStream*" | fillnull | stats count min(_time) as firstTime
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max(_time) as lastTime by dest signature signature_id user_id vendor_product EventID
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Guid Opcode Name Path ProcessID ScriptBlockId ScriptBlockText | `security_content_ctime(firstTime)`
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| `security_content_ctime(lastTime)` | `powershell_webrequest_using_memory_stream_filter`'
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how_to_implement: The following analytic requires PowerShell operational logs to be
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imported. Modify the powershell macro as needed to match the sourcetype or add index.
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This analytic is specific to 4104, or PowerShell Script Block Logging.
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known_false_positives: Unknown, possible custom scripting.
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references:
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- https://www.mandiant.com/resources/blog/tracking-evolution-gootloader-operations
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- https://thedfirreport.com/2022/05/09/seo-poisoning-a-gootloader-story/
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- https://attack.mitre.org/techniques/T1059/001/
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drilldown_searches:
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- name: View the detection results for - "$dest$" and "$user$"
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search: '%original_detection_search% | search dest = "$dest$" user = "$user$"'
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earliest_offset: $info_min_time$
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latest_offset: $info_max_time$
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- name: View risk events for the last 7 days for - "$dest$" and "$user$"
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search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$dest$",
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"$user$") starthoursago=168 | stats count min(_time) as firstTime max(_time)
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as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk
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Message" values(analyticstories) as "Analytic Stories" values(annotations._all)
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as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics"
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by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
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earliest_offset: $info_min_time$
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latest_offset: $info_max_time$
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rba:
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message: Powershell webrequest to memory stream behavior. Possible fileless malware
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staging on $dest$ by $user_id$.
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risk_objects:
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- field: dest
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type: system
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score: 80
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- field: user_id
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type: user
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score: 80
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threat_objects: []
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tags:
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analytic_story:
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- MoonPeak
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- Medusa Ransomware
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- Malicious PowerShell
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- PHP-CGI RCE Attack on Japanese Organizations
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asset_type: Endpoint
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mitre_attack_id:
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- T1059.001
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- T1105
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- T1027.011
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product:
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- Splunk Enterprise
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- Splunk Enterprise Security
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- Splunk Cloud
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security_domain: endpoint
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tests:
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- name: True Positive Test
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attack_data:
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- data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/malware/gootloader/partial_ttps/windows-powershell-xml.log
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source: XmlWinEventLog:Microsoft-Windows-PowerShell/Operational
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sourcetype: XmlWinEventLog
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