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https://github.com/splunk/security_content
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Michael Haag
80 lines
2.9 KiB
YAML
80 lines
2.9 KiB
YAML
name: CertUtil With Decode Argument
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id: bfe94226-8c10-11eb-a4b3-acde48001122
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version: 2
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date: '2021-03-23'
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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: 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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data_source:
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- Sysmon Event ID 1
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search:
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selection1:
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OriginalFileName: CertUtil.exe
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selection2:
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Image|endswith: certutil.exe
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selection3:
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CommandLine: '*decode*'
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condition: (selection1 or selection2) and selection3
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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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- Forest Blizzard
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asset_type: Endpoint
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confidence: 80
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impact: 50
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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 $user$ attempting to decode a file.
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mitre_attack_id:
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- T1140
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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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risk_score: 40
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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/attack_techniques/T1140/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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