Detection: Linux Binary Executed from Shared Memory Directory

Description

The following analytic identifies the execution of a binary by root from Linux shared memory directories (/dev/shm/ and /run/shm/). Threat actors place executables in these directories to persist on high-uptime servers as system backdoors. Both /dev/shm and /run/shm are tmpfs-backed directories that exist only in virtual memory with no persistent storage, making them attractive for staging fileless or semi-fileless malware while avoiding disk forensics.

Search

 1
 2| tstats `security_content_summariesonly`
 3  count min(_time) as firstTime
 4        max(_time) as lastTime
 5
 6from datamodel=Endpoint.Processes where
 7
 8Processes.process_path IN (
 9    "/dev/shm/*",
10    "/run/shm/*"
11)
12Processes.user=root
13
14by Processes.process Processes.process_path Processes.process_name Processes.user
15   Processes.user_id Processes.process_hash Processes.parent_process_name
16   Processes.parent_process_path Processes.parent_process Processes.parent_process_guid
17   Processes.parent_process_id Processes.process_guid Processes.process_id
18   Processes.vendor_product Processes.action Processes.dest
19   Processes.process_current_directory Processes.process_integrity_level
20   Processes.original_file_name
21
22
23| `drop_dm_object_name(Processes)`
24
25| `security_content_ctime(firstTime)`
26
27| `security_content_ctime(lastTime)`
28
29| `linux_binary_executed_from_shared_memory_directory_filter`

Data Source

Name	Platform	Sourcetype	Source
Sysmon for Linux EventID 1	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 the process GUID, process name, and parent process. Additionally, you must ingest complete command-line executions. 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 Processes 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 applications may use shared memory directories for temporary file storage or inter-process communication. Verify any flagged activity against known software behavior and filter accordingly.

Associated Analytic Story

• Linux Post-Exploitation

• Linux Privilege Escalation

• Linux Persistence Techniques

• Compromised Linux Host

Intermediate Findings

Threat Objects

References

• https://linuxsecurity.com/features/fileless-malware-on-linux

• https://twitter.com/GossiTheDog/status/1522964028284411907

• https://github.com/elastic/detection-rules/blob/main/rules/linux/execution_process_started_in_shared_memory_directory.toml

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