mirror of
https://github.com/splunk/security_content
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Bhavin Patel
105 lines
4.2 KiB
YAML
105 lines
4.2 KiB
YAML
name: Any Powershell DownloadString
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id: 4d015ef2-7adf-11eb-95da-acde48001122
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version: 4
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date: '2024-05-10'
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author: Michael Haag, Splunk
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status: production
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type: TTP
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description: The following analytic detects the use of PowerShell's `DownloadString`
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method to download files. It leverages data from Endpoint Detection and Response
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(EDR) agents, focusing on process execution logs that include command-line details.
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This activity is significant because `DownloadString` is commonly used in malicious
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PowerShell scripts to fetch and execute remote code. If confirmed malicious, this
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behavior could allow an attacker to download and run arbitrary code, potentially
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leading to unauthorized access, data exfiltration, or further compromise of the
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affected system.
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data_source:
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- Sysmon EventID 1
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search: '| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time)
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as lastTime from datamodel=Endpoint.Processes where `process_powershell` Processes.process=*.DownloadString* by
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Processes.dest Processes.user Processes.parent_process Processes.parent_process_name
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Processes.process_name Processes.original_file_name Processes.process Processes.process_id
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Processes.parent_process_id | `drop_dm_object_name(Processes)` | `security_content_ctime(firstTime)`|
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`security_content_ctime(lastTime)`| `any_powershell_downloadstring_filter`'
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how_to_implement: The detection is based on data that originates from Endpoint Detection
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and Response (EDR) agents. These agents are designed to provide security-related
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telemetry from the endpoints where the agent is installed. To implement this search,
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you must ingest logs that contain the process GUID, process name, and parent process.
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Additionally, you must ingest complete command-line executions. These logs must
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be processed using the appropriate Splunk Technology Add-ons that are specific to
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the EDR product. The logs must also be mapped to the `Processes` node of the `Endpoint`
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data model. Use the Splunk Common Information Model (CIM) to normalize the field
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names and speed up the data modeling process.
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known_false_positives: False positives may be present and filtering will need to occur
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by parent process or command line argument. It may be required to modify this query
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to an EDR product for more granular coverage.
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references:
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- https://docs.microsoft.com/en-us/dotnet/api/system.net.webclient.downloadstring?view=net-5.0
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- https://blog.malwarebytes.com/malwarebytes-news/2021/02/lazyscripter-from-empire-to-double-rat/
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- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1059.001/T1059.001.md
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- https://thedfirreport.com/2023/05/22/icedid-macro-ends-in-nokoyawa-ransomware/
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tags:
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analytic_story:
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- Winter Vivern
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- Ingress Tool Transfer
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- Hermetic Wiper
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- Malicious PowerShell
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- HAFNIUM Group
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- Data Destruction
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- IcedID
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- SysAid On-Prem Software CVE-2023-47246 Vulnerability
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- Phemedrone Stealer
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asset_type: Endpoint
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confidence: 70
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impact: 80
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message: An instance of $parent_process_name$ spawning $process_name$ was identified
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on endpoint $dest$ by user $user$. This behavior identifies the use of DownloadString
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within PowerShell.
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mitre_attack_id:
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- T1059
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- T1059.001
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- T1105
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observable:
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- name: user
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type: User
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role:
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- Victim
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- name: dest
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type: Hostname
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role:
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- Victim
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- name: parent_process_name
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type: Process
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role:
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- Parent Process
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- name: process_name
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type: Process
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role:
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- Child Process
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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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required_fields:
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- _time
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- Processes.dest
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- Processes.user
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- Processes.parent_process_name
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- Processes.parent_process
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- Processes.original_file_name
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- Processes.process_name
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- Processes.process
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- Processes.process_id
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- Processes.parent_process_path
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- Processes.process_path
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- Processes.parent_process_id
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risk_score: 56
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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:
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https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1059.001/atomic_red_team/windows-sysmon.log
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source: XmlWinEventLog:Microsoft-Windows-Sysmon/Operational
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sourcetype: xmlwineventlog
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