This analytic is to detect a deletion of ssh key in a linux machine. attacker may delete or modify ssh key to impair some security features or act as defense evasion in compromised linux machine. This Anomaly can be also a good indicator of a malware trying to wipe or delete several files in a compromised host as part of its destructive payload like what acidrain malware does in linux or router machines. This detection can be a good pivot to check what process and user tries to delete this type of files which is not so common and need further investigation.
- Type: Anomaly
- Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
- Datamodel: Endpoint
- Last Updated: 2022-04-12
- Author: Teoderick Contreras, Splunk
- ID: 73a56508-1cf5-4df7-b8d9-5737fbdc27d2
Kill Chain Phase
- CIS 3
- CIS 5
- CIS 16
1 2 3 4 5 6 7 8 9 10 11 | 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 | `drop_dm_object_name(Filesystem)` |rename process_guid as proc_guid |join proc_guid, _time [ | tstats `security_content_summariesonly` count FROM datamodel=Endpoint.Processes where Processes.parent_process_name != unknown by _time span=1h Processes.process_id Processes.process_name Processes.process Processes.dest Processes.parent_process_name Processes.parent_process Processes.process_path Processes.process_guid | `drop_dm_object_name(Processes)` |rename process_guid as proc_guid | fields _time dest user parent_process_name parent_process process_name process_path process proc_guid registry_path registry_value_name registry_value_data registry_key_name action] | table process_name process proc_guid file_name file_path action _time parent_process_name parent_process process_path dest user | `linux_account_manipulation_of_ssh_config_and_keys_filter`
The SPL above uses the following Macros:
linux_account_manipulation_of_ssh_config_and_keys_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.
How To Implement
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
|49.0||70||70||a $process_name$ deleting a SSH key in $dest$|
The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.
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