Detection: Linux Auditd Possible Access To Sudoers File

Updated Date: 2025-11-27 ID: 8be88f46-f7e8-4ae6-b15e-cf1b13392834 Author: Teoderick Contreras, Nasreddine Bencherchali, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

The following analytic detects potential access or modification of the /etc/sudoers file on a Linux system. It leverages data from Linux Auditd, focusing on events of type PATH or CWD. This activity could be significant because the sudoers file controls user permissions for executing commands with elevated privileges. Correlate this with related EXECVE or PROCTITLE events to identify the process or user responsible for the access or modification. If confirmed malicious, an attacker could gain persistence or escalate privileges, compromising the security of the targeted host.

Search

 1`linux_auditd`
 2(type=PATH OR type=CWD)
 3
 4| rex "msg=audit\([^)]*:(?<audit_id>\d+)\)"
 5
 6
 7| stats
 8  values(type) as types
 9  values(name) as names
10  values(nametype) as nametype
11  values(cwd) as cwd_list
12  values(_time) as event_times
13  by audit_id, host
14
15
16| eval current_working_directory = coalesce(mvindex(cwd_list, 0), "N/A")
17
18| eval candidate_paths = mvmap(names, if(match(names, "^/"), names, current_working_directory + "/" + names))
19
20| eval matched_paths = mvfilter(match(candidate_paths, "/etc/sudoers.*"))
21
22| eval match_count = mvcount(matched_paths)
23
24| eval reconstructed_path = mvindex(matched_paths, 0)
25
26| eval e_time = mvindex(event_times, 0)
27
28| where match_count > 0
29
30| rename host as dest
31
32
33| stats count min(e_time) as firstTime max(e_time) as lastTime
34  values(nametype) as nametype
35  by current_working_directory
36     reconstructed_path
37     match_count
38     dest
39     audit_id
40
41
42| `security_content_ctime(firstTime)`
43
44| `security_content_ctime(lastTime)`
45
46| `linux_auditd_possible_access_to_sudoers_file_filter`

Data Source

Name	Platform	Sourcetype	Source
Linux Auditd Cwd	Linux	`'auditd'`	`'auditd'`
Linux Auditd Path	Linux	`'auditd'`	`'auditd'`

Macros Used

Name	Value
linux_auditd	`sourcetype="auditd"`
linux_auditd_possible_access_to_sudoers_file_filter	`search *`

linux_auditd_possible_access_to_sudoers_file_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
T1548.003	Sudo and Sudo Caching	Defense Evasion

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 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 and make sure the type=CWD record type is activate in your auditd configuration. 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

Risk Based Analytics (RBA)

Risk Message:

$reconstructed_path$ has been accessed for potential modification or deletion on host - [$dest$]

Risk Object	Risk Object Type	Risk Score	Threat Objects
dest	system	25	No Threat Objects

References

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	✅ Passing	N/A	N/A	N/A
Unit	✅ Passing	Dataset	`auditd`	`auditd`
Integration	✅ Passing	Dataset	`auditd`	`auditd`

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: 11