sigma-rules/rules/linux/impact_potential_linux_ransomware_note_detected.toml

[metadata]
creation_date = "2023/03/20"
integration = ["endpoint"]
maturity = "production"
min_stack_comments = "New fields added: required_fields, related_integrations, setup"
min_stack_version = "8.3.0"
updated_date = "2023/08/22"

[rule]
author = ["Elastic"]
description = """
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. 
"""
from = "now-9m"
index = ["logs-endpoint.events.*"]
language = "eql"
license = "Elastic License v2"
name = "Potential Linux Ransomware Note Creation Detected"
risk_score = 47
rule_id = "c8935a8b-634a-4449-98f7-bb24d3b2c0af"
severity = "medium"
tags = ["Domain: Endpoint", "OS: Linux", "Use Case: Threat Detection", "Tactic: Impact"]
type = "eql"
query = '''
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*"
  )]
'''

[[rule.threat]]
framework = "MITRE ATT&CK"

[[rule.threat.technique]]
id = "T1486"
name = "Data Encrypted for Impact"
reference = "https://attack.mitre.org/techniques/T1486/"

[rule.threat.tactic]
id = "TA0040"
name = "Impact"
reference = "https://attack.mitre.org/tactics/TA0040/"