Detection: Linux Auditd Find Ssh Private Keys

Updated Date: 2025-01-16 ID: e2d2bd10-dcd1-4b2f-8a76-0198eab32ba5 Author: Teoderick Contreras, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic detects suspicious attempts to find SSH private keys, which may indicate an attacker's effort to compromise secure access to systems. SSH private keys are essential for secure authentication, and unauthorized access to these keys can enable attackers to gain unauthorized access to servers and other critical infrastructure. By monitoring for unusual or unauthorized searches for SSH private keys, this analytic helps identify potential threats to network security, allowing security teams to quickly respond and safeguard against unauthorized access and potential breaches.

Search

1`linux_auditd` `linux_auditd_normalized_execve_process` 
2| rename host as dest 
3| rename comm as process_name 
4| rename exe as process 
5| where  (LIKE (process_exec, "%find%") OR LIKE (process_exec, "%grep%")) AND (LIKE (process_exec, "%id_rsa%") OR LIKE (process_exec, "%id_dsa%")OR LIKE (process_exec, "%.key%") OR LIKE (process_exec, "%ssh_key%")OR LIKE (process_exec, "%authorized_keys%")) 
6| stats count min(_time) as firstTime max(_time) as lastTime by argc process_exec dest 
7| `security_content_ctime(firstTime)` 
8| `security_content_ctime(lastTime)`
9| `linux_auditd_find_ssh_private_keys_filter`

Data Source

Name	Platform	Sourcetype	Source
Linux Auditd Execve	Linux	`'linux:audit'`	`'/var/log/audit/audit.log'`

Macros Used

Name	Value
linux_auditd	`sourcetype="linux:audit"`
linux_auditd_find_ssh_private_keys_filter	`search *`

linux_auditd_find_ssh_private_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
T1552.004	Private Keys	Credential Access
T1552	Unsecured Credentials	Credential Access

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 implement this detection, the process begins by ingesting auditd data, that consists of SYSCALL, TYPE, EXECVE and PROCTITLE events, which captures command-line executions and process details on Unix/Linux systems. These logs should be ingested and processed using Splunk Add-on for Unix and Linux (https://splunkbase.splunk.com/app/833), which is essential for correctly parsing and categorizing the data. The next step involves normalizing the field names to match the field names set by the Splunk Common Information Model (CIM) to ensure consistency across different data sources and enhance the efficiency of data modeling. This approach enables effective monitoring and detection of linux endpoints where auditd is deployed

Known False Positives

Administrator or network operator can use this application for automation purposes. Please update the filter macros to remove false positives.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message:

A [$process_exec$] event occurred on host - [$dest$] to find SSH private keys.

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	`/var/log/audit/audit.log`	`linux:audit`
Integration	✅ Passing	Dataset	`/var/log/audit/audit.log`	`linux:audit`

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: 3