LoFP LoFP / legitimate processes may be spawned from the microsoft exchange server unified messaging (um) service. if known processes are causing false positives, they can be exempted from the rule.

Techniques

Sample rules

Microsoft Exchange Server UM Spawning Suspicious Processes

Description

Identifies suspicious processes being spawned by the Microsoft Exchange Server Unified Messaging (UM) service. This activity has been observed exploiting CVE-2021-26857.

Detection logic

process where host.os.type == "windows" and event.type == "start" and
  process.parent.name : ("UMService.exe", "UMWorkerProcess.exe") and
    not process.executable : (
          "?:\\Windows\\System32\\werfault.exe",
          "?:\\Windows\\System32\\wermgr.exe",
          "?:\\Program Files\\Microsoft\\Exchange Server\\V??\\Bin\\UMWorkerProcess.exe",
          "?:\\Program Files\\Microsoft\\Exchange Server\\Bin\\UMWorkerProcess.exe",
          "D:\\Exchange 2016\\Bin\\UMWorkerProcess.exe",
          "E:\\ExchangeServer\\Bin\\UMWorkerProcess.exe",
          "D:\\Exchange\\Bin\\UMWorkerProcess.exe",
          "D:\\Exchange Server\\Bin\\UMWorkerProcess.exe",
          "E:\\Exchange Server\\V15\\Bin\\UMWorkerProcess.exe",
          "\\Device\\HarddiskVolume?\\Windows\\System32\\werfault.exe",
          "\\Device\\HarddiskVolume?\\Windows\\System32\\wermgr.exe",
          "\\Device\\HarddiskVolume?\\Program Files\\Microsoft\\Exchange Server\\V??\\Bin\\UMWorkerProcess.exe",
          "\\Device\\HarddiskVolume?\\Program Files\\Microsoft\\Exchange Server\\Bin\\UMWorkerProcess.exe",
          "\\Device\\HarddiskVolume?\\Exchange 2016\\Bin\\UMWorkerProcess.exe",
          "\\Device\\HarddiskVolume?\\ExchangeServer\\Bin\\UMWorkerProcess.exe",
          "\\Device\\HarddiskVolume?\\Exchange\\Bin\\UMWorkerProcess.exe",
          "\\Device\\HarddiskVolume?\\Exchange Server\\Bin\\UMWorkerProcess.exe",
          "\\Device\\HarddiskVolume?\\Exchange Server\\V15\\Bin\\UMWorkerProcess.exe"
    )