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Potential Linux Ransomware Note Creation Detected

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Potential Linux Ransomware Note Creation Detected

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This rule identifies a sequence of a mass file encryption event in conjunction with the creation of a .txt file with a file name containing ransomware keywords executed by the same process in a 1 second timespan. Ransomware is a type of malware that encrypts a victim’s files or systems and demands payment (usually in cryptocurrency) in exchange for the decryption key. One important indicator of a ransomware attack is the mass encryption of the file system, after which a new file extension is added to the file.

Rule type: eql

Rule indices:

  • logs-endpoint.events.*

Severity: medium

Risk score: 47

Runs every: 5m

Searches indices from: now-9m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

References: None

Tags:

  • Domain: Endpoint
  • OS: Linux
  • Use Case: Threat Detection
  • Tactic: Impact
  • Data Source: Elastic Defend

Version: 5

Rule authors:

  • Elastic

Rule license: Elastic License v2

Rule query

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sequence by host.id, process.entity_id with maxspan=1s
  [file where host.os.type == "linux" and event.type == "change" and event.action == "rename" and file.extension : "?*"
   and ((process.name in ("bash", "dash", "sh", "tcsh", "csh", "zsh", "ksh", "fish", "ash", "openssl")) or
   (process.executable : ("./*", "/tmp/*", "/var/tmp/*", "/dev/shm/*", "/var/run/*", "/boot/*", "/srv/*", "/run/*"))) and
   file.path : (
   "/home/*/Downloads/*", "/home/*/Documents/*", "/root/*", "/bin/*", "/usr/bin/*",
   "/opt/*", "/etc/*", "/var/log/*", "/var/lib/log/*", "/var/backup/*", "/var/www/*") and not ((
   process.name : (
   "dpkg", "yum", "dnf", "rpm", "dockerd", "go", "java", "pip*", "python*", "node", "containerd", "php", "p4d",
   "conda", "chrome", "imap", "cmake", "firefox", "semanage", "semodule", "ansible-galaxy", "fc-cache", "jammy", "git",
   "systemsettings", "vmis-launcher")) or (file.path : "/etc/selinux/*") or (file.extension in ("qmlc", "txt")
   ))] with runs=25
  [file where host.os.type == "linux" and event.action == "creation" and file.name : (
   "*crypt*", "*restore*", "*lock*", "*recovery*", "*data*", "*read*", "*instruction*", "*how_to*", "*ransom*"
  )]

Framework: MITRE ATT&CKTM

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