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. Generally, a ransomware note with contact details is dropped onto the file system which can be used by the victim to contact the attacker. 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.

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: 2

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 != "" ] with runs=50
  [ file where host.os.type == "linux" and event.action == "creation" and
  file.extension == "txt" and file.name : (
    "*crypt*",
    "*restore*",
    "*lock*",
    "*recovery*",
    "*data*",
    "*read*",
    "*instruction*",
    "*how_to*",
    "*ransom*"
    ) ] | tail 1