rules/linux/defense_evasion_symlink_binary_to_writable_dir.toml

[metadata]
creation_date = "2025/04/30"
integration = ["endpoint"]
maturity = "production"
updated_date = "2025/04/30"

[rule]
author = ["Elastic"]
description = """
This rule detects the creation of a symbolic link from a system binary to a suspicious and writable location. This
activity may indicate an attacker's attempt to evade detection by behavioral rules that depend on predefined process
parent/child relationships. By executing the symlinked variant of a binary instead of the original, the attacker aims to
bypass these rules. Through the new_terms rule type, this rule can identify uncommon parent processes that may indicate the
presence of a malicious symlink.
"""
from = "now-9m"
index = [
    "logs-endpoint.events.process*",
]
language = "kuery"
license = "Elastic License v2"
name = "System Binary Symlink to Suspicious Location"
risk_score = 21
rule_id = "d19a2399-f8e2-4b10-80d8-a561ce9d24d1"
severity = "low"
tags = [
    "Domain: Endpoint",
    "OS: Linux",
    "Use Case: Threat Detection",
    "Tactic: Defense Evasion",
    "Data Source: Elastic Defend",
]
timestamp_override = "event.ingested"
type = "new_terms"
query = '''
host.os.type:linux and event.category:process and event.type:start and event.action:exec and process.parent.executable:* and
(process.name:ln or process.name:busybox and process.args:ln or process.name:cp and process.args:--symbolic-link) and
process.args:(
  (
    /bin/* or /lib/* or /lib64/* or /sbin/* or /usr/bin/* or /usr/lib/* or /usr/lib64/* or /usr/local/bin/* or
    /usr/local/lib/* or /usr/local/lib64/* or /usr/local/sbin/* or /usr/sbin/*
  ) and (
    /*/.* or /dev/shm/* or /home/* or /root/* or /tmp/* or /var/tmp/*
  ) and
  not (/usr/bin/coreutils or /tmp/mkinitcpio* or /var/tmp/dracut* or /var/tmp/mkinitramfs*)
)
'''

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

  [rule.threat.tactic]
  name = "Defense Evasion"
  id = "TA0005"
  reference = "https://attack.mitre.org/tactics/TA0005/"

    [[rule.threat.technique]]
    name = "Hijack Execution Flow"
    id = "T1574"
    reference = "https://attack.mitre.org/techniques/T1574/"

    [[rule.threat.technique]]
    name = "Indirect Command Execution"
    id = "T1202"
    reference = "https://attack.mitre.org/techniques/T1202/"

    [[rule.threat.technique]]
    name = "Hide Artifacts"
    id = "T1564"
    reference = "https://attack.mitre.org/techniques/T1564/"

[rule.new_terms]
field = "new_terms_fields"
value = ["host.id", "process.parent.name"]

[[rule.new_terms.history_window_start]]
field = "history_window_start"
value = "now-10d"