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Detection rules › Sigma

Exchange PowerShell Snap-Ins Usage

Status
test
Severity
high
Log source
product windows, category process_creation
Author
FPT.EagleEye, Nasreddine Bencherchali (Nextron Systems)
Source
github.com/SigmaHQ/sigma

Detects adding and using Exchange PowerShell snap-ins to export mailbox data. As seen used by HAFNIUM and APT27

MITRE ATT&CK coverage

TacticTechniques
ExecutionT1059.001 Command and Scripting Interpreter: PowerShell
CollectionT1114 Email Collection

Event coverage

ProviderEventTitle
SysmonEvent ID 1Process creation

Rule body yaml

title: Exchange PowerShell Snap-Ins Usage
id: 25676e10-2121-446e-80a4-71ff8506af47
status: test
description: Detects adding and using Exchange PowerShell snap-ins to export mailbox data. As seen used by HAFNIUM and APT27
references:
    - https://www.volexity.com/blog/2021/03/02/active-exploitation-of-microsoft-exchange-zero-day-vulnerabilities/
    - https://www.microsoft.com/security/blog/2021/03/02/hafnium-targeting-exchange-servers/
    - https://www.intrinsec.com/apt27-analysis/
author: FPT.EagleEye, Nasreddine Bencherchali (Nextron Systems)
date: 2021-03-03
modified: 2023-03-24
tags:
    - attack.execution
    - attack.t1059.001
    - attack.collection
    - attack.t1114
logsource:
    category: process_creation
    product: windows
detection:
    selection_img:
        - Image|endswith:
              - '\powershell.exe'
              - '\pwsh.exe'
        - OriginalFileName:
              - 'PowerShell.EXE'
              - 'pwsh.dll'
    selection_cli:
        CommandLine|contains: 'Add-PSSnapin'
    selection_module:
        CommandLine|contains:
            - 'Microsoft.Exchange.Powershell.Snapin'
            - 'Microsoft.Exchange.Management.PowerShell.SnapIn'
    filter_msiexec:
        # ParentCommandLine: C:\Windows\System32\MsiExec.exe -Embedding C9138ECE2536CB4821EB5F55D300D88E E Global\MSI0000
        ParentImage: 'C:\Windows\System32\msiexec.exe'
        CommandLine|contains: '$exserver=Get-ExchangeServer ([Environment]::MachineName) -ErrorVariable exerr 2> $null'
    condition: all of selection_* and not 1 of filter_*
falsepositives:
    - Unknown
level: high

Stages and Predicates

Stage 0: condition

all of selection_* and not 1 of filter_*

Stage 1: selection_img

selection_img:
    - Image|endswith:
          - '\powershell.exe'
          - '\pwsh.exe'
    - OriginalFileName:
          - 'PowerShell.EXE'
          - 'pwsh.dll'

Stage 2: selection_cli

selection_cli:
    CommandLine|contains: 'Add-PSSnapin'

Stage 3: selection_module

selection_module:
    CommandLine|contains:
        - 'Microsoft.Exchange.Powershell.Snapin'
        - 'Microsoft.Exchange.Management.PowerShell.SnapIn'

Stage 4: not filter_msiexec

filter_msiexec:
    ParentImage: 'C:\Windows\System32\msiexec.exe'
    CommandLine|contains: '$exserver=Get-ExchangeServer ([Environment]::MachineName) -ErrorVariable exerr 2> $null'

Exclusions

Top-level NOT(...) conjuncts: predicates this rule actively suppresses.

FieldKindExcluded values
CommandLinematch$exserver=Get-ExchangeServer ([Environment]::MachineName) -ErrorVariable exerr 2> $null
ParentImageeqC:\Windows\System32\msiexec.exe

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

FieldKindValues
CommandLinematch
  • Add-PSSnapin corpus 3 (sigma 2, kusto 1)
  • Microsoft.Exchange.Management.PowerShell.SnapIn
  • Microsoft.Exchange.Powershell.Snapin
Imageends_with
  • \powershell.exe corpus 182 (sigma 182)
  • \pwsh.exe corpus 168 (sigma 168)
OriginalFileNameeq
  • PowerShell.EXE corpus 120 (sigma 84, splunk 30, elastic 6)
  • pwsh.dll corpus 112 (sigma 79, splunk 30, elastic 3)