Elastic medium stable kql

Roshal Archive (RAR) or PowerShell File Downloaded from the Internet

Detects a Roshal Archive (RAR) file or PowerShell script downloaded from the internet by an internal host. Gaining initial access to a system and then downloading encoded or encrypted tools to move laterally is a common practice for adversaries as a way to protect their more valuable tools and tactics, techniques, and procedures (TTPs). This may be atypical behavior for a managed network and can be indicative of malware, exfiltration, or command and control.

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Detection Logic

(data_stream.dataset: (network_traffic.http or network_traffic.tls or fortinet_fortigate.log) or
  (data_stream.dataset: panw.panos and network.application: "web-browsing") or
  (event.category: (network or network_traffic) and network.protocol: http)) and
  (url.extension:(ps1 or rar) or url.path:(*.ps1 or *.rar)) and
    not destination.ip:(
      10.0.0.0/8 or
      127.0.0.0/8 or
      169.254.0.0/16 or
      172.16.0.0/12 or
      192.0.0.0/24 or
      192.0.0.0/29 or
      192.0.0.8/32 or
      192.0.0.9/32 or
      192.0.0.10/32 or
      192.0.0.170/32 or
      192.0.0.171/32 or
      192.0.2.0/24 or
      192.31.196.0/24 or
      192.52.193.0/24 or
      192.168.0.0/16 or
      192.88.99.0/24 or
      224.0.0.0/4 or
      100.64.0.0/10 or
      192.175.48.0/24 or
      198.18.0.0/15 or
      198.51.100.0/24 or
      203.0.113.0/24 or
      240.0.0.0/4 or
      "::1" or
      "FE80::/10" or
      "FF00::/8"
    ) and
    source.ip:(
      10.0.0.0/8 or
      172.16.0.0/12 or
      192.168.0.0/16
    )

False Positives

⚠ Downloading RAR or PowerShell files from the Internet may be expected for certain systems. This rule should be tailored to either exclude systems as sources or destinations in which this behavior is expected.

Field Validations

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