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patel-bhavin
97 lines
4.0 KiB
YAML
97 lines
4.0 KiB
YAML
name: Windows CertUtil Decode File
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id: b06983f4-8f72-11ec-ab50-acde48001122
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version: 1
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date: '2022-02-16'
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author: Michael Haag, Splunk
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type: TTP
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datamodel:
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- Endpoint_Processes
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description: CertUtil.exe may be used to `encode` and `decode` a file, including PE
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and script code. Encoding will convert a file to base64 with `-----BEGIN CERTIFICATE-----`
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and `-----END CERTIFICATE-----` tags. Malicious usage will include decoding a encoded
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file that was downloaded. Once decoded, it will be loaded by a parallel process.
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Note that there are two additional command switches that may be used - `encodehex`
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and `decodehex`. Similarly, the file will be encoded in HEX and later decoded for
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further execution. During triage, identify the source of the file being decoded.
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Review its contents or execution behavior for further analysis.
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search: '| from read_ssa_enriched_events() | where "Endpoint_Processes" IN(_datamodels)
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| eval timestamp=parse_long(ucast(map_get(input_event, "_time"), "string", null)),
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cmd_line=ucast(map_get(input_event, "process"), "string", null), process_name=ucast(map_get(input_event,
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"process_name"), "string", null), process_path=ucast(map_get(input_event, "process_path"),
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"string", null), parent_process_name=ucast(map_get(input_event, "parent_process_name"),
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"string", null), event_id=ucast(map_get(input_event, "event_id"), "string", null)
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| where cmd_line IS NOT NULL AND process_name IS NOT NULL AND process_name="certutil.exe"
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AND (like (cmd_line, "%decode%")) | eval start_time=timestamp, end_time=timestamp,
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entities=mvappend(ucast(map_get(input_event, "dest_user_id"), "string", null), ucast(map_get(input_event,
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"dest_device_id"), "string", null)) | eval body=create_map(["event_id", event_id,
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"cmd_line", cmd_line, "process_name", process_name, "parent_process_name", parent_process_name,
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"process_path", process_path]) | into write_ssa_detected_events();'
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how_to_implement: To successfully implement this search you need to be ingesting information
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on process that include the name of the process responsible for the changes from
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your endpoints into the `Endpoint` datamodel in the `Processes` node. In addition,
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confirm the latest CIM App 4.20 or higher is installed and the latest TA for the
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endpoint product.
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known_false_positives: Typically seen used to `encode` files, but it is possible to
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see legitimate use of `decode`. Filter based on parent-child relationship, file
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paths, endpoint or user.
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references:
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- https://attack.mitre.org/techniques/T1140/
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- https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1140/T1140.md
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- https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/certutil
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- https://www.bleepingcomputer.com/news/security/certutilexe-could-allow-attackers-to-download-malware-while-bypassing-av/
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tags:
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analytic_story:
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- Deobfuscate-Decode Files or Information
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- Living Off The Land
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automated_detection_testing: passed
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confidence: 80
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context:
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- Source:Endpoint
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- Stage:Execution
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dataset:
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- https://media.githubusercontent.com/media/splunk/attack_data/ master/datasets/attack_techniques/T1140/atomic_red_team/encode-windows-security.log
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impact: 50
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cis20:
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- CIS 8
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nist:
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- PR.PT
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- DE.CM
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kill_chain_phases:
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- Exploitation
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message: An instance of $parent_process_name$ spawning $process_name$ was identified
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on endpoint $dest_device_id$ by user $dest_user_id$ attempting to decode a file
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on disk.
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mitre_attack_id:
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- T1140
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observable:
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- name: dest_user_id
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type: User
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role:
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- Victim
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- name: dest_device_id
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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 Behavioral Analytics
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required_fields:
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- _time
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- dest_device_id
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- process_name
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- parent_process_name
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- process_path
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- dest_user_id
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- process
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- cmd_line
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risk_score: 40
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security_domain: endpoint
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asset_type: Endpoint
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