This rule identifies a sequence of 100 file extension rename events within a set of common file paths by the same process in a timespan of 1 second. 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:

Severity: high

Risk score: 73

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:

Version: 3

Rule authors:

Rule license: Elastic License v2

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
    file.path : (
      "/home/*", "/etc/*", "/root/*", "/opt/*", "/var/backups/*", "/var/lib/log/*"
      ) and not
    file.extension : (
      "xml", "json", "conf", "dat", "gz", "info", "mod", "final",
      "php", "pyc", "log", "bak", "bin", "csv", "pdf", "cfg", "*old"
      ) and not
    process.name : (
      "dpkg",  "yum", "dnf", "rpm", "dockerd"
    ) ] with runs=100 | tail 1