Detection: Linux Auditd Doas Conf File Creation

Updated Date: 2025-11-27 ID: 61059783-574b-40d2-ac2f-69b898afd6b4 Author: Teoderick Contreras, Nasreddine Bencherchali, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic detects the creation of the doas.conf file on a Linux host. This file is used by the doas utility to allow standard users to perform tasks as root, similar to sudo. The detection leverages Linux Auditd data, focusing on the creation of the doas.conf file. This activity is significant because it can indicate an attempt to gain elevated privileges, potentially by an adversary. If confirmed malicious, this could allow an attacker to execute commands with root commands with root privileges, leading to full system compromise.

Search

 1`linux_auditd`
 2(
 3  (type=PATH nametype="CREATE")
 4  OR
 5  type=CWD
 6)
 7
 8| rex "msg=audit\([^)]*:(?<audit_id>\d+)\)"
 9
10
11| stats
12  values(type) as types
13  values(name) as names
14  values(nametype) as nametype
15  values(cwd) as cwd_list
16  values(_time) as event_times
17  by audit_id host
18
19
20| eval current_working_directory = coalesce(mvindex(cwd_list, 0), "N/A")
21
22| eval candidate_paths = mvmap(names, if(match(names, "^/"), names, current_working_directory + "/" + names))
23
24| eval matched_paths = mvfilter(match(candidate_paths, "/etc/doas.conf.*"))
25
26| eval match_count = mvcount(matched_paths)
27
28| eval reconstructed_path = mvindex(matched_paths, 0)
29
30| eval e_time = mvindex(event_times, 0)
31
32| where match_count > 0
33
34| rename host as dest
35
36
37| stats count min(e_time) as firstTime max(e_time) as lastTime
38  values(nametype) as nametype
39  by current_working_directory
40     reconstructed_path
41     match_count
42     dest
43     audit_id
44
45
46| `security_content_ctime(firstTime)`
47
48| `security_content_ctime(lastTime)`
49
50| table nametype current_working_directory reconstructed_path dest audit_id match_count firstTime lastTime
51
52| `linux_auditd_doas_conf_file_creation_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_doas_conf_file_creation_filter	`search *`

linux_auditd_doas_conf_file_creation_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.CM

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 Notable	Yes
Rule Title	`%name%`
Rule Description	`%description%`
Notable Event Fields	user, dest
Creates Risk Event	True

This configuration file applies to all detections of type TTP. These detections will use Risk Based Alerting and generate Notable Events.

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:

A $reconstructed_path$ file was created on host - [$dest$]

Risk Object	Risk Object Type	Risk Score	Threat Objects
dest	system	64	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: 8