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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

Version: 4

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
    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
  [ 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*"
      ) and not process.name : ("go", "java", "pip*", "python*", "node", "containerd") ] | tail 1

Framework: MITRE ATT&CK^TM

Tactic:
- Name: Impact
- ID: TA0040
- Reference URL: https://attack.mitre.org/tactics/TA0040/
Technique:
- Name: Data Encrypted for Impact
- ID: T1486
- Reference URL: https://attack.mitre.org/techniques/T1486/

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