Detection: Linux Auditd Unix Shell Configuration Modification

Updated Date: 2025-11-27 ID: 66f737c6-3f7f-46ed-8e9b-cc0e5bf01f04 Author: Teoderick Contreras, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic detects suspicious access or modifications to Unix shell configuration files, which may indicate an attempt to alter system behavior or gain unauthorized access. Unix shell configuration files, such as .bashrc or .profile, control user environment settings and command execution. Unauthorized changes to these files can be used to execute malicious commands, escalate privileges, or hide malicious activities. By monitoring for unusual or unauthorized modifications to shell configuration files, this analytic helps identify potential security threats, allowing security teams to respond quickly and mitigate risks. Correlate this with related EXECVE or PROCTITLE events to identify the process or user responsible for the access or modification.

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/profile
21|/etc/shells
22|/etc/profile\\.d/.*
23|/etc/bash\\.bashrc.*
24|/etc/bashrc
25|.*/zsh/zprofile
26|.*/zsh/zshrc
27|.*/zsh/zlogin
28|.*/zsh/zlogout
29|/etc/csh\\.cshrc.*
30|/etc/csh\\.login.*
31|/root/\\.bashrc.*
32|/root/\\.bash_profile.*
33|/root/\\.profile.*
34|/root/\\.zshrc.*
35|/root/\\.zprofile.*
36|/home/.*/\\.bashrc.*
37|/home/.*/\\.zshrc.*
38|/home/.*/\\.bash_profile.*
39|/home/.*/\\.zprofile.*
40|/home/.*/\\.profile.*
41|/home/.*/\\.bash_login.*
42|/home/.*/\\.bash_logout.*
43|/home/.*/\\.zlogin.*
44|/home/.*/\\.zlogout.*"))
45
46| eval match_count = mvcount(matched_paths)
47
48| eval reconstructed_path = mvindex(matched_paths, 0)
49
50| eval e_time = mvindex(event_times, 0)
51
52| where match_count > 0
53
54| rename host as dest
55
56
57| stats count min(e_time) as firstTime max(e_time) as lastTime
58  values(nametype) as nametype
59  by current_working_directory
60     reconstructed_path
61     match_count
62     dest
63     audit_id
64
65
66| `security_content_ctime(firstTime)`
67
68| `security_content_ctime(lastTime)`
69
70| `linux_auditd_unix_shell_configuration_modification_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_unix_shell_configuration_modification_filter	`search *`

linux_auditd_unix_shell_configuration_modification_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
T1546.004	Unix Shell Configuration Modification	Persistence

Exploitation

Installation

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 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 [$nametype$] event occurred on host - [$dest$] to modify the unix shell configuration file.

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