Detection: Linux Account Manipulation Of SSH Config and Keys

Updated Date: 2024-11-13 ID: 73a56508-1cf5-4df7-b8d9-5737fbdc27d2 Author: Teoderick Contreras, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic detects the deletion of SSH keys on a Linux machine. It leverages filesystem event logs to identify when files within "/etc/ssh/" or "~/.ssh/" are deleted. This activity is significant because attackers may delete or modify SSH keys to evade security measures or as part of a destructive payload, similar to the AcidRain malware. If confirmed malicious, this behavior could lead to impaired security features, hindered forensic investigations, or further unauthorized access, necessitating immediate investigation to identify the responsible process and user.

1
2| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime FROM datamodel=Endpoint.Filesystem where Filesystem.action=deleted AND Filesystem.file_path IN ("/etc/ssh/*", "~/.ssh/*") by _time span=1h Filesystem.file_name Filesystem.file_path Filesystem.dest Filesystem.process_guid Filesystem.action 
3| `drop_dm_object_name(Filesystem)` 
4| `security_content_ctime(firstTime)` 
5| `security_content_ctime(lastTime)`
6| `linux_account_manipulation_of_ssh_config_and_keys_filter`

Data Source

Name Platform Sourcetype Source
Sysmon for Linux EventID 11 Linux icon 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_account_manipulation_of_ssh_config_and_keys_filter search *
linux_account_manipulation_of_ssh_config_and_keys_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
ID Technique Tactic
T1485 Data Destruction Impact
T1070.004 File Deletion Defense Evasion
T1070 Indicator Removal Defense Evasion
Actions on Objectives
Exploitation
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 Risk Event True
This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

Implementation

To successfully implement this search, you need to be ingesting logs with the process name, parent process, and command-line executions from your endpoints. If you are using Sysmon, you can use the Add-on for Linux Sysmon from Splunkbase.

Known False Positives

Administrator or network operator can execute this command. Please update the filter macros to remove false positives.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message:

SSH Config and keys are deleted on $dest$ by Process GUID - $process_guid$

Risk Object Risk Object Type Risk Score Threat Objects
dest system 49 No Threat Objects

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: 5