sigma-rules/rules/cross-platform/persistence_ssh_authorized_keys_modification.toml

[metadata]
creation_date = "2020/12/22"
integration = ["endpoint"]
maturity = "production"
min_stack_comments = "Multiple field support in the New Terms rule type was added in Elastic 8.6"
min_stack_version = "8.6.0"
updated_date = "2023/09/22"

[rule]
author = ["Elastic"]
description = """
The Secure Shell (SSH) authorized_keys file specifies which users are allowed to log into a server using public key
authentication. Adversaries may modify it to maintain persistence on a victim host by adding their own public key(s).
"""
from = "now-9m"
index = ["auditbeat-*", "logs-endpoint.events.*"]
language = "kuery"
license = "Elastic License v2"
name = "SSH Authorized Keys File Modification"
risk_score = 47
rule_id = "2215b8bd-1759-4ffa-8ab8-55c8e6b32e7f"
severity = "medium"
tags = ["Domain: Endpoint",
        "OS: Linux",
        "OS: macOS",
        "Use Case: Threat Detection",
        "Tactic: Lateral Movement",
        "Tactic: Persistence",
        "Data Source: Elastic Defend"
        ]
timestamp_override = "event.ingested"
type = "new_terms"

query = '''
event.category:file and event.type:(change or creation) and
 file.name:("authorized_keys" or "authorized_keys2" or "/etc/ssh/sshd_config" or "/root/.ssh") and
 not process.executable:
             (/Library/Developer/CommandLineTools/usr/bin/git or
              /usr/local/Cellar/maven/*/libexec/bin/mvn or
              /Library/Java/JavaVirtualMachines/jdk*.jdk/Contents/Home/bin/java or
              /usr/bin/vim or
              /usr/local/Cellar/coreutils/*/bin/gcat or
              /usr/bin/bsdtar or
              /usr/bin/nautilus or
              /usr/bin/scp or
              /usr/bin/touch or
              /var/lib/docker/* or
              /usr/bin/google_guest_agent or 
              /opt/jc/bin/jumpcloud-agent)
'''

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

[[rule.threat.technique]]
id = "T1098"
name = "Account Manipulation"
reference = "https://attack.mitre.org/techniques/T1098/"

[[rule.threat.technique.subtechnique]]
id = "T1098.004"
name = "SSH Authorized Keys"
reference = "https://attack.mitre.org/techniques/T1098/004/"

[rule.threat.tactic]
id = "TA0003"
name = "Persistence"
reference = "https://attack.mitre.org/tactics/TA0003/"

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

[[rule.threat.technique]]
id = "T1563"
name = "Remote Service Session Hijacking"
reference = "https://attack.mitre.org/techniques/T1563/"

[[rule.threat.technique.subtechnique]]
id = "T1563.001"
name = "SSH Hijacking"
reference = "https://attack.mitre.org/techniques/T1563/001/"

[[rule.threat.technique]]
id = "T1021"
name = "Remote Services"
reference = "https://attack.mitre.org/techniques/T1021/"

[[rule.threat.technique.subtechnique]]
id = "T1021.004"
name = "SSH"
reference = "https://attack.mitre.org/techniques/T1021/004/"

[rule.threat.tactic]
id = "TA0008"
name = "Lateral Movement"
reference = "https://attack.mitre.org/tactics/TA0008/"

[rule.new_terms]
field = "new_terms_fields"
value = ["host.id", "process.executable", "file.path"]

[[rule.new_terms.history_window_start]]
field = "history_window_start"
value = "now-7d"