launching-base64-powershell[Nobelium]

id: fd25665b-9376-4c38-b046-76757eff0e40
name: launching-base64-powershell[Nobelium]
description: |
  This query was originally published in the threat analytics report, Solorigate supply chain attack. Please note that these attacks are currently known as the Nobelium campaign.
  Microsoft detects the 2020 SolarWinds supply chain attack implant and its other components as part of a campaign by the Nobelium activity group. Nobelium is the threat actor behind the attack against SolarWinds, which was previously referred to as Solorigate.
  Nobelium silently added malicious code to legitimate software updates for Orion, which is IT monitoring software provided by SolarWinds. In this way, malicious dynamic link libraries (DLLs) were distributed to SolarWinds customers.
  The following query detects events when SolarWinds processes launched PowerShell commands that were possibly encoded in Base64. Attackers may encode PowerShell commands in Base64 to obfuscate malicious activity.
  More Nobelium-related queries can be found listed under the See also section of this document.
  References:
  https://msrc-blog.microsoft.com/2020/12/13/customer-guidance-on-recent-nation-state-cyber-attacks/
  https://www.microsoft.com/security/blog/2020/12/18/analyzing-solorigate-the-compromised-dll-file-that-started-a-sophisticated-cyberattack-and-how-microsoft-defender-helps-protect/
requiredDataConnectors:
- connectorId: MicrosoftThreatProtection
  dataTypes:
  - DeviceProcessEvents
tactics:
- Execution
- Defense evasion
tags:
- Nobelium
query: |
  DeviceProcessEvents
  | where InitiatingProcessFileName =~ "SolarWinds.BusinessLayerHost.exe"
  | where FileName =~ "powershell.exe"
  // Extract base64 encoded string, ensure valid base64 length
  | extend base64_extracted = extract('([A-Za-z0-9+/]{20,}[=]{0,3})', 1, ProcessCommandLine)
  | extend base64_extracted = substring(base64_extracted, 0, (strlen(base64_extracted) / 4) * 4)
  | extend base64_decoded = replace(@'\0', '', make_string(base64_decode_toarray(base64_extracted)))
  //
  | where notempty(base64_extracted) and base64_extracted matches regex '[A-Z]' and base64_extracted matches regex '[0-9]'