| ID | Technique | Tactic |
|---|---|---|
| T1037 | Boot or Logon Initialization Scripts | Persistence |
| T1059.004 | Unix Shell | Privilege Escalation |
| T1547 | Boot or Logon Autostart Execution | Execution |
Detection: Linux MOTD Script Added
Description
The following analytic detects the creation of a file within the /etc/update-motd.d directory. This is used to add scripts that run with Message of the Day (MOTD) when a user logs in. This can be used by attackers for persistence if it contains malicious code.
Search
1
2| tstats `security_content_summariesonly`
3 count min(_time) as firstTime
4 max(_time) as lastTime
5
6from datamodel=Endpoint.Filesystem where
7
8Filesystem.file_path="/etc/update-motd.d/*"
9Filesystem.action IN ("created", "modified")
10
11by Filesystem.file_path Filesystem.file_name
12 Filesystem.user Filesystem.dest
13 Filesystem.action Filesystem.process_guid
14 Filesystem.process_id
15
16
17| `drop_dm_object_name(Filesystem)`
18
19| `security_content_ctime(firstTime)`
20
21| `security_content_ctime(lastTime)`
22
23| `linux_motd_script_added_filter`
Data Source
| Name | Platform | Sourcetype | Source |
|---|---|---|---|
| Sysmon for Linux EventID 11 |  Linux |
'sysmon:linux' |
'Syslog:Linux-Sysmon/Operational' |
Macros Used
| Name | Value |
|---|---|
| security_content_ctime | convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$) |
| linux_motd_script_added_filter | search * |
linux_motd_script_added_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.
Annotations
MITRE ATT&CK
Kill Chain Phases
NIST
CIS
Threat Actors
Exploitation
Installation
DE.AE
CIS 10
Default Configuration
This detection is configured by default in Splunk Enterprise Security to run with the following settings:
| Setting | Value |
|---|---|
| Disabled | true |
| Cron Schedule | 0 * * * * |
| Earliest Time | -70m@m |
| Latest Time | -10m@m |
| Schedule Window | auto |
| Creates Finding (Notable) | No |
| Creates Intermediate Finding (Risk Event) | Yes |
Anomaly detections generate Intermediate Findings (Risk Events). They do not generate a Finding (Notable) directly.
Implementation
The detection is based on data that originates from Endpoint Detection and Response (EDR) agents. These agents are designed to provide security-related telemetry from the endpoints where the agent is installed. To implement this search, you must ingest logs that contain file creation events including the file path and user context. These logs must be processed using the appropriate Splunk Technology Add-ons that are specific to the EDR product. The logs must also be mapped to the Filesystem node of the Endpoint data model. Use the Splunk Common Information Model (CIM) to normalize the field names and speed up the data modeling process.
Known False Positives
Legitimate system administrators may add or modify MOTD scripts for valid operational purposes such as displaying system information or login banners. Filter based on known administrative activity and authorized users.
Associated Analytic Story
Intermediate Findings
| Message | Entity Field | Entity Type | Risk Score |
|---|---|---|---|
| Potential MOTD Script [$file_name$] added by [$user$] on [$dest$]. | dest | system | 20 |
Threat Objects
| Field | Type |
|---|---|
| file_name | file_name |
References
Detection Testing
| Test Type | Status | Dataset | Source | Sourcetype |
|---|---|---|---|---|
| Validation | ✅ Passing | N/A | N/A | N/A |
| Unit | ✅ Passing | Dataset | Syslog:Linux-Sysmon/Operational |
sysmon:linux |
| Integration | ✅ Passing | Dataset | Syslog:Linux-Sysmon/Operational |
sysmon:linux |
Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI.
Alternatively you can replay a dataset into a Splunk Attack Range
Source: GitHub |
Version: 1