Potential Persistence Through MOTD File Creation Detected

  1[metadata]
  2creation_date = "2023/02/28"
  3integration = ["endpoint"]
  4maturity = "production"
  5min_stack_comments = "Multiple field support in the New Terms rule type was added in Elastic 8.6"
  6min_stack_version = "8.6.0"
  7updated_date = "2024/02/21"
  8
  9[transform]
 10[[transform.osquery]]
 11label = "Osquery - Retrieve File Information"
 12query = "SELECT * FROM file WHERE path = {{file.path}}"
 13
 14[[transform.osquery]]
 15label = "Osquery - Retrieve File Listing Information"
 16query = "SELECT * FROM file WHERE (path LIKE '/etc/update-motd.d/%' OR path LIKE '/usr/lib/update-notifier/%')"
 17
 18[[transform.osquery]]
 19label = "Osquery - Retrieve Additional File Listing Information"
 20query = """
 21SELECT
 22  f.path,
 23  u.username AS file_owner,
 24  g.groupname AS group_owner,
 25  datetime(f.atime, 'unixepoch') AS file_last_access_time,
 26  datetime(f.mtime, 'unixepoch') AS file_last_modified_time,
 27  datetime(f.ctime, 'unixepoch') AS file_last_status_change_time,
 28  datetime(f.btime, 'unixepoch') AS file_created_time,
 29  f.size AS size_bytes
 30FROM
 31  file f
 32  LEFT JOIN users u ON f.uid = u.uid
 33  LEFT JOIN groups g ON f.gid = g.gid
 34WHERE (path LIKE '/etc/update-motd.d/%' OR path LIKE '/usr/lib/update-notifier/%')
 35"""
 36
 37[[transform.osquery]]
 38label = "Osquery - Retrieve Running Processes by User"
 39query = "SELECT pid, username, name FROM processes p JOIN users u ON u.uid = p.uid ORDER BY username"
 40
 41[[transform.osquery]]
 42label = "Osquery - Retrieve Crontab Information"
 43query = "SELECT * FROM crontab"
 44
 45[rule]
 46author = ["Elastic"]
 47description = """
 48Message of the day (MOTD) is the message that is presented to the user when a user connects to a Linux server via SSH or
 49a serial connection. Linux systems contain several default MOTD files located in the "/etc/update-motd.d/" and
 50"/usr/lib/update-notifier/" directories. These scripts run as the root user every time a user connects over SSH or a
 51serial connection. Adversaries may create malicious MOTD files that grant them persistence onto the target every time a
 52user connects to the system by executing a backdoor script or command. This rule detects the creation of potentially
 53malicious files within the default MOTD file directories.
 54"""
 55from = "now-9m"
 56index = ["logs-endpoint.events.*", "endgame-*"]
 57language = "kuery"
 58license = "Elastic License v2"
 59name = "Potential Persistence Through MOTD File Creation Detected"
 60note = """## Triage and analysis
 61
 62### Investigating Potential Persistence Through MOTD File Creation Detected
 63
 64The message-of-the-day (MOTD) is used to display a customizable system-wide message or information to users upon login in Linux.
 65
 66Attackers can abuse message-of-the-day (motd) files to run scripts, commands or malicious software every time a user connects to a system over SSH or a serial connection, by creating a new file within the `/etc/update-motd.d/` or `/usr/lib/update-notifier/` directory. Executable files in these directories automatically run with root privileges.
 67
 68This rule identifies the creation of new files within the `/etc/update-motd.d/` or `/usr/lib/update-notifier/` directories.
 69
 70> **Note**:
 71> This investigation guide uses the [Osquery Markdown Plugin](https://www.elastic.co/guide/en/security/master/invest-guide-run-osquery.html) introduced in Elastic Stack version 8.5.0. Older Elastic Stack versions will display unrendered Markdown in this guide.
 72> This investigation guide uses [placeholder fields](https://www.elastic.co/guide/en/security/current/osquery-placeholder-fields.html) to dynamically pass alert data into Osquery queries. Placeholder fields were introduced in Elastic Stack version 8.7.0. If you're using Elastic Stack version 8.6.0 or earlier, you'll need to manually adjust this investigation guide's queries to ensure they properly run.
 73
 74#### Possible Investigation Steps
 75
 76- Investigate the file that was created or modified.
 77  - $osquery_0
 78- Investigate whether any other files in the `/etc/update-motd.d/` or `/usr/lib/update-notifier/` directories have been altered.
 79  - $osquery_1
 80  - $osquery_2
 81- Investigate the script execution chain (parent process tree) for unknown processes. Examine their executable files for prevalence and whether they are located in expected locations.
 82  - $osquery_3
 83- Investigate other alerts associated with the user/host during the past 48 hours.
 84- Investigate whether the modified scripts call other malicious scripts elsewhere on the file system.
 85  - If scripts or executables were dropped, retrieve the files and determine if they are malicious:
 86    - Use a private sandboxed malware analysis system to perform analysis.
 87      - Observe and collect information about the following activities:
 88        - Attempts to contact external domains and addresses.
 89          - Check if the domain is newly registered or unexpected.
 90          - Check the reputation of the domain or IP address.
 91        - File access, modification, and creation activities.
 92        - Cron jobs, services and other persistence mechanisms.
 93            - $osquery_4
 94
 95### Related Rules
 96
 97- Suspicious Process Spawned from MOTD Detected - 4ec47004-b34a-42e6-8003-376a123ea447
 98
 99### False positive analysis
100
101- This activity is unlikely to happen legitimately. Any activity that triggered the alert and is not inherently malicious must be monitored by the security team.
102
103### Response and remediation
104
105- Initiate the incident response process based on the outcome of the triage.
106- Isolate the involved host to prevent further post-compromise behavior.
107- If the triage identified malware, search the environment for additional compromised hosts.
108  - Implement temporary network rules, procedures, and segmentation to contain the malware.
109  - Stop suspicious processes.
110  - Immediately block the identified indicators of compromise (IoCs).
111  - Inspect the affected systems for additional malware backdoors like reverse shells, reverse proxies, or droppers that attackers could use to reinfect the system.
112- Investigate credential exposure on systems compromised or used by the attacker to ensure all compromised accounts are identified. Reset passwords for these accounts and other potentially compromised credentials, such as email, business systems, and web services.
113- Delete the MOTD files or restore their original configuration.
114- Run a full antimalware scan. This may reveal additional artifacts left in the system, persistence mechanisms, and malware components.
115- Determine the initial vector abused by the attacker and take action to prevent reinfection through the same vector.
116- Leverage the incident response data and logging to improve the mean time to detect (MTTD) and the mean time to respond (MTTR).
117"""
118references = [
119    "https://pberba.github.io/security/2022/02/06/linux-threat-hunting-for-persistence-initialization-scripts-and-shell-configuration/#10-boot-or-logon-initialization-scripts-motd"
120]
121risk_score = 47
122rule_id = "96d11d31-9a79-480f-8401-da28b194608f"
123setup = """## Setup
124
125This rule requires data coming in from Elastic Defend.
126
127### Elastic Defend Integration Setup
128Elastic 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.
129
130#### Prerequisite Requirements:
131- Fleet is required for Elastic Defend.
132- To configure Fleet Server refer to the [documentation](https://www.elastic.co/guide/en/fleet/current/fleet-server.html).
133
134#### The following steps should be executed in order to add the Elastic Defend integration on a Linux System:
135- Go to the Kibana home page and click "Add integrations".
136- In the query bar, search for "Elastic Defend" and select the integration to see more details about it.
137- Click "Add Elastic Defend".
138- Configure the integration name and optionally add a description.
139- Select the type of environment you want to protect, either "Traditional Endpoints" or "Cloud Workloads".
140- 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).
141- We suggest selecting "Complete EDR (Endpoint Detection and Response)" as a configuration setting, that provides "All events; all preventions"
142- 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.
143For more details on Elastic Agent configuration settings, refer to the [helper guide](https://www.elastic.co/guide/en/fleet/8.10/agent-policy.html).
144- Click "Save and Continue".
145- 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.
146For more details on Elastic Defend refer to the [helper guide](https://www.elastic.co/guide/en/security/current/install-endpoint.html).
147"""
148severity = "medium"
149tags = [
150        "Domain: Endpoint",
151        "OS: Linux",
152        "Use Case: Threat Detection",
153        "Tactic: Persistence",
154        "Data Source: Elastic Endgame",
155        "Resources: Investigation Guide",
156        "Data Source: Elastic Defend"
157        ]
158type = "new_terms"
159timestamp_override = "event.ingested"
160query = '''
161host.os.type :linux and event.action:(creation or file_create_event or rename or file_rename_event) and
162file.path : (/etc/update-motd.d/* or /usr/lib/update-notifier/*) and not process.name : (
163  dpkg or dockerd or rpm or executor or dnf or podman or ln or yum 
164) and not (
165  (process.name:mv and file.extension:dpkg-remove) or
166  (file.extension:(swp or swpx))
167)
168'''
169
170[[rule.threat]]
171framework = "MITRE ATT&CK"
172
173[[rule.threat.technique]]
174id = "T1037"
175name = "Boot or Logon Initialization Scripts"
176reference = "https://attack.mitre.org/techniques/T1037/"
177
178[rule.threat.tactic]
179id = "TA0003"
180name = "Persistence"
181reference = "https://attack.mitre.org/tactics/TA0003/"
182
183[rule.new_terms]
184field = "new_terms_fields"
185value = ["host.id", "file.path", "process.executable"]
186
187[[rule.new_terms.history_window_start]]
188field = "history_window_start"
189value = "now-10d"