Detection: Linux Auditd Preload Hijack Via Preload File

Description

The following analytic detects suspicious preload hijacking via the preload file, which may indicate an attacker's attempt to intercept or manipulate library loading processes. The preload file can be used to force the loading of specific libraries before others, potentially allowing malicious code to execute or alter application behavior. By monitoring for unusual or unauthorized modifications to the preload file, this analytic helps identify attempts to hijack preload mechanisms, enabling security teams to investigate and address potential threats to system integrity and security. 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/ld.so.preload.*"))
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_preload_hijack_via_preload_file_filter`

Data Source

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

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 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

• Compromised Linux Host

• Linux Living Off The Land

• Linux Persistence Techniques

• Linux Privilege Escalation

Risk Based Analytics (RBA)

Risk Message:

A [$nametype$] event has occurred on host - [$dest$] to modify the preload file.

References

• https://www.splunk.com/en_us/blog/security/deep-dive-on-persistence-privilege-escalation-technique-and-detection-in-linux-platform.html

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: 8