Detection: Linux Auditd Possible Access To Credential Files

Description

The following analytic detects attempts to access or dump the contents of /etc/passwd and /etc/shadow files on Linux systems. It leverages data from Linux Auditd, focusing on processes like 'cat', 'nano', 'vim', and 'vi' accessing these files. This activity is significant as it may indicate credential dumping, a technique used by adversaries to gain persistence or escalate privileges. If confirmed malicious, privileges. If confirmed malicious, attackers could obtain hashed passwords for offline cracking, leading to unauthorized access and potential system compromise.

Search

1`linux_auditd` `linux_auditd_normalized_proctitle_process` 
2| rename host as dest 
3| where (LIKE (process_exec, "%shadow%") OR LIKE (process_exec, "%passwd%")) AND (LIKE (process_exec, "%cat %") OR LIKE (process_exec, "%nano %")OR LIKE (process_exec, "%vim %") OR LIKE (process_exec, "%vi %")) 
4| stats count min(_time) as firstTime max(_time) as lastTime by process_exec proctitle normalized_proctitle_delimiter dest 
5| `security_content_ctime(firstTime)` 
6| `security_content_ctime(lastTime)`
7| `linux_auditd_possible_access_to_credential_files_filter`

Data Source

Name	Platform	Sourcetype	Source	Supported App
Linux Auditd Proctitle	Linux	'linux:audit'	'/var/log/audit/audit.log'	N/A

Macros Used

Annotations

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Implementation

To implement this detection, the process begins by ingesting auditd data, that consist 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 execute this command. Please update the filter macros to remove false positives.

Associated Analytic Story

• Compromised Linux Host

• Linux Persistence Techniques

• Linux Privilege Escalation

Risk Based Analytics (RBA)

References

• https://askubuntu.com/questions/445361/what-is-difference-between-etc-shadow-and-etc-passwd

• https://attack.mitre.org/techniques/T1003/008/

Detection Testing

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