Detection: Linux Possible System Binary Backdoor

Description

The following analytic detects the creation or overwrite of commonly targeted Linux system binaries such as cat, ls, cp, ps, mv, netstat, ss, and lsof. Adversaries may replace these utilities with backdoored versions to hide malicious activity, harvest credentials, or maintain persistence while appearing to use legitimate system tools. This technique is associated with rootkit deployment and post-exploitation frameworks such as PANIX.

Search

 1
 2| tstats `security_content_summariesonly`
 3  count min(_time) as firstTime max(_time) as lastTime
 4
 5from datamodel=Endpoint.Filesystem where
 6
 7Filesystem.file_path IN (
 8    "/usr/bin/cat",
 9    "/usr/bin/cp",
10    "/usr/bin/ls",
11    "/usr/bin/lsof",
12    "/usr/bin/mv",
13    "/usr/bin/netstat",
14    "/usr/bin/ps",
15    "/usr/bin/ss"
16)
17
18by Filesystem.file_path Filesystem.file_name Filesystem.user Filesystem.dest
19   Filesystem.action Filesystem.process_guid Filesystem.process_id
20
21
22| `drop_dm_object_name(Filesystem)`
23
24| `security_content_ctime(firstTime)`
25
26| `security_content_ctime(lastTime)`
27
28| `linux_possible_system_binary_backdoor_filter`

Data Source

Name	Platform	Sourcetype	Source
Sysmon for Linux EventID 11	Linux	'sysmon:linux'	'Syslog:Linux-Sysmon/Operational'

Macros Used

Annotations

Default Configuration

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

Implementation

The detection is based on data that originates from Endpoint Detection and Response (EDR) agents. These agents are designed to provide security-related telemetry from the endpoints where the agent is installed. To implement this search, you must ingest logs that contain file creation events including the file path and user context. These logs must be processed using the appropriate Splunk Technology Add-ons that are specific to the EDR product. The logs must also be mapped to the Filesystem node of the Endpoint data model. Use the Splunk Common Information Model (CIM) to normalize the field names and speed up the data modeling process.

Known False Positives

Legitimate system updates or package managers may create or overwrite system binaries during normal operations. Filter for known update processes and package management activity to reduce noise.

Associated Analytic Story

• Linux Post-Exploitation

• Linux Privilege Escalation

• Linux Persistence Techniques

• Compromised Linux Host

Intermediate Findings

Threat Objects

References

• https://github.com/Aegrah/PANIX

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