sigma-rules/rules/linux/privilege_escalation_linux_suspicious_symbolic_link.toml

[metadata]
creation_date = "2023/07/27"
integration = ["endpoint"]
maturity = "production"
min_stack_comments = "New fields added: required_fields, related_integrations, setup"
min_stack_version = "8.3.0"
updated_date = "2023/10/16"

[rule]
author = ["Elastic"]
description = """
Identifies the creation of a symbolic link to a suspicious file or location. A symbolic link is a reference to a file or
directory that acts as a pointer or shortcut, allowing users to access the target file or directory from a different
location in the file system. An attacker can potentially leverage symbolic links for privilege escalation by tricking a
privileged process into following the symbolic link to a sensitive file, giving the attacker access to data or
capabilities they would not normally have.
"""
from = "now-9m"
index = ["logs-endpoint.events.*", "endgame-*"]
language = "eql"
license = "Elastic License v2"
name = "Suspicious Symbolic Link Created"
risk_score = 21
rule_id = "8a024633-c444-45c0-a4fe-78128d8c1ab6"
setup = """

This rule requires data coming in from Elastic Defend.

### Elastic Defend Integration Setup
Elastic Defend is integrated into the Elastic Agent using Fleet. Upon configuration, the integration allows
the Elastic Agent to monitor events on your host and send data to the Elastic Security app.

#### Prerequisite Requirements:
- Fleet is required for Elastic Defend.
- To configure Fleet Server refer to the [documentation](https://www.elastic.co/guide/en/fleet/current/fleet-server.html).

#### The following steps should be executed in order to add the Elastic Defend integration on a Linux System:
- Go to the Kibana home page and click Add integrations.
- In the query bar, search for Elastic Defend and select the integration to see more details about it.
- Click Add Elastic Defend.
- Configure the integration name and optionally add a description.
- Select the type of environment you want to protect, either Traditional Endpoints or Cloud Workloads.
- Select a configuration preset. Each preset comes with different default settings for Elastic Agent, you can further customize these later by configuring the Elastic Defend integration policy. [Helper guide](https://www.elastic.co/guide/en/security/current/configure-endpoint-integration-policy.html).
- We suggest to select "Complete EDR (Endpoint Detection and Response)" as a configuration setting, that provides "All events; all preventions"
- Enter a name for the agent policy in New agent policy name. If other agent policies already exist, you can click the Existing hosts tab and select an existing policy instead.
For more details on Elastic Agent configuration settings, refer to the [helper guide](https://www.elastic.co/guide/en/fleet/8.10/agent-policy.html).
- Click Save and Continue.
- To complete the integration, select Add Elastic Agent to your hosts and continue to the next section to install the Elastic Agent on your hosts.
For more details on Elastic Defend refer to the [helper guide](https://www.elastic.co/guide/en/security/current/install-endpoint.html).

"""
severity = "low"
tags = ["Domain: Endpoint", "OS: Linux", "Use Case: Threat Detection", "Tactic: Privilege Escalation", "Tactic: Credential Access", "Data Source: Elastic Endgame", "Data Source: Elastic Defend"]
timestamp_override = "event.ingested"
type = "eql"
query = '''
process where host.os.type == "linux" and event.action in ("exec", "exec_event") and
event.type == "start" and process.name == "ln" and process.args in ("-s", "-sf") and 
  (
    /* suspicious files */
    (process.args in ("/etc/shadow", "/etc/shadow-", "/etc/shadow~", "/etc/gshadow", "/etc/gshadow-") or 
    (process.working_directory == "/etc" and process.args in ("shadow", "shadow-", "shadow~", "gshadow", "gshadow-"))) or 
    
    /* suspicious bins */
    (process.args in ("/bin/bash", "/bin/dash", "/bin/sh", "/bin/tcsh", "/bin/csh", "/bin/zsh", "/bin/ksh", "/bin/fish") or 
    (process.working_directory == "/bin" and process.args : ("bash", "dash", "sh", "tcsh", "csh", "zsh", "ksh", "fish"))) or 
    (process.args in ("/usr/bin/bash", "/usr/bin/dash", "/usr/bin/sh", "/usr/bin/tcsh", "/usr/bin/csh", "/usr/bin/zsh", "/usr/bin/ksh", "/usr/bin/fish") or 
    (process.working_directory == "/usr/bin" and process.args in ("bash", "dash", "sh", "tcsh", "csh", "zsh", "ksh", "fish"))) or
    
    /* suspicious locations */
    (process.args : ("/etc/cron.d/*", "/etc/cron.daily/*", "/etc/cron.hourly/*", "/etc/cron.weekly/*", "/etc/cron.monthly/*")) or
    (process.args : ("/home/*/.ssh/*", "/root/.ssh/*","/etc/sudoers.d/*", "/dev/shm/*"))
  ) and 
  process.parent.name in ("bash", "dash", "ash", "sh", "tcsh", "csh", "zsh", "ksh", "fish") and 
  not user.Ext.real.id == "0" and not group.Ext.real.id == "0"
'''

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

[[rule.threat.technique]]
id = "T1548"
name = "Abuse Elevation Control Mechanism"
reference = "https://attack.mitre.org/techniques/T1548/"

[rule.threat.tactic]
id = "TA0004"
name = "Privilege Escalation"
reference = "https://attack.mitre.org/tactics/TA0004/"

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

[[rule.threat.technique]]
id = "T1003"
name = "OS Credential Dumping"
reference = "https://attack.mitre.org/techniques/T1003/"

[[rule.threat.technique.subtechnique]]
id = "T1003.008"
name = "/etc/passwd and /etc/shadow"
reference = "https://attack.mitre.org/techniques/T1003/008/"

[rule.threat.tactic]
id = "TA0006"
name = "Credential Access"
reference = "https://attack.mitre.org/tactics/TA0006/"