Process executed from binary hidden in Base64 encoded file

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Id	d6190dde-8fd2-456a-ac5b-0a32400b0464
Rulename	Process executed from binary hidden in Base64 encoded file
Description	Encoding malicious software is a technique used to obfuscate files from detection. The first CommandLine component is looking for Python decoding base64. The second CommandLine component is looking for Bash/sh command line base64 decoding. The third one is looking for Ruby decoding base64.
Severity	Medium
Tactics	Execution DefenseEvasion
Techniques	T1059 T1027 T1140
Required data connectors	SecurityEvents WindowsForwardedEvents WindowsSecurityEvents
Kind	Scheduled
Query frequency	1d
Query period	1d
Trigger threshold	0
Trigger operator	gt
Source Uri	https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Endpoint Threat Protection Essentials/Analytic Rules/execute_base64_decodedpayload.yaml
Version	1.1.3
Arm template	d6190dde-8fd2-456a-ac5b-0a32400b0464.json

KQL

let ProcessCreationEvents=(union isfuzzy=true
(SecurityEvent
| where EventID==4688
| where isnotempty(CommandLine)
| project TimeGenerated, Computer, Account = SubjectUserName, AccountDomain = SubjectDomainName, FileName = Process, CommandLine, ParentProcessName
),
(WindowsEvent
| where EventID==4688
| where EventData has_any (".decode('base64')", "base64 --decode", ".decode64(" )
| extend CommandLine = tostring(EventData.CommandLine)
| where isnotempty(CommandLine)
| extend SubjectUserName = tostring(EventData.SubjectUserName)
| extend SubjectDomainName = tostring(EventData.SubjectDomainName)
| extend NewProcessName = tostring(EventData.NewProcessName)
| extend FileName=tostring(split(NewProcessName, '\\')[-1])
| extend ParentProcessName = tostring(EventData.ParentProcessName)
| project TimeGenerated, Computer, Account = SubjectUserName, AccountDomain = SubjectDomainName, CommandLine, ParentProcessName
));
ProcessCreationEvents 
| where CommandLine contains ".decode('base64')"
        or CommandLine contains "base64 --decode"
        or CommandLine contains ".decode64(" 
| summarize StartTimeUtc = min(TimeGenerated), EndTimeUtc = max(TimeGenerated), CountToday = count() by Computer, Account, AccountDomain, FileName, CommandLine, ParentProcessName
| extend HostName = iif(Computer has '.',substring(Computer,0,indexof(Computer,'.')),Computer) , DnsDomain = iif(Computer has '.',substring(Computer,indexof(Computer,'.')+1),'')

YAML

description: |
  'Encoding malicious software is a technique used to obfuscate files from detection. 
  The first CommandLine component is looking for Python decoding base64. 
  The second CommandLine component is looking for Bash/sh command line base64 decoding.
  The third one is looking for Ruby decoding base64.'  
kind: Scheduled
tactics:
- Execution
- DefenseEvasion
requiredDataConnectors:
- connectorId: SecurityEvents
  dataTypes:
  - SecurityEvent
- connectorId: WindowsSecurityEvents
  dataTypes:
  - SecurityEvent
- connectorId: WindowsSecurityEvents
  dataTypes:
  - SecurityEvents
- connectorId: WindowsForwardedEvents
  dataTypes:
  - WindowsEvent
OriginalUri: https://github.com/Azure/Azure-Sentinel/blob/master/Solutions/Endpoint Threat Protection Essentials/Analytic Rules/execute_base64_decodedpayload.yaml
severity: Medium
name: Process executed from binary hidden in Base64 encoded file
triggerThreshold: 0
queryPeriod: 1d
query: |
  let ProcessCreationEvents=(union isfuzzy=true
  (SecurityEvent
  | where EventID==4688
  | where isnotempty(CommandLine)
  | project TimeGenerated, Computer, Account = SubjectUserName, AccountDomain = SubjectDomainName, FileName = Process, CommandLine, ParentProcessName
  ),
  (WindowsEvent
  | where EventID==4688
  | where EventData has_any (".decode('base64')", "base64 --decode", ".decode64(" )
  | extend CommandLine = tostring(EventData.CommandLine)
  | where isnotempty(CommandLine)
  | extend SubjectUserName = tostring(EventData.SubjectUserName)
  | extend SubjectDomainName = tostring(EventData.SubjectDomainName)
  | extend NewProcessName = tostring(EventData.NewProcessName)
  | extend FileName=tostring(split(NewProcessName, '\\')[-1])
  | extend ParentProcessName = tostring(EventData.ParentProcessName)
  | project TimeGenerated, Computer, Account = SubjectUserName, AccountDomain = SubjectDomainName, CommandLine, ParentProcessName
  ));
  ProcessCreationEvents 
  | where CommandLine contains ".decode('base64')"
          or CommandLine contains "base64 --decode"
          or CommandLine contains ".decode64(" 
  | summarize StartTimeUtc = min(TimeGenerated), EndTimeUtc = max(TimeGenerated), CountToday = count() by Computer, Account, AccountDomain, FileName, CommandLine, ParentProcessName
  | extend HostName = iif(Computer has '.',substring(Computer,0,indexof(Computer,'.')),Computer) , DnsDomain = iif(Computer has '.',substring(Computer,indexof(Computer,'.')+1),'')  
relevantTechniques:
- T1059
- T1027
- T1140
id: d6190dde-8fd2-456a-ac5b-0a32400b0464
queryFrequency: 1d
status: Available
triggerOperator: gt
version: 1.1.3
entityMappings:
- entityType: Account
  fieldMappings:
  - columnName: Account
    identifier: Name
- entityType: Host
  fieldMappings:
  - columnName: Computer
    identifier: FullName
  - columnName: HostName
    identifier: HostName
  - columnName: DnsDomain
    identifier: DnsDomain

ARM