splunk-security_content/docs/_posts/2022-07-27-linux_decode_base64_to_shell.md

title, excerpt, categories, last_modified_at, toc, toc_label, tags

title	excerpt	categories	last_modified_at	toc	toc_label	tags
Linux Decode Base64 to Shell	Obfuscated Files or Information , Unix Shell	Endpoint	2022-07-27	true		Obfuscated Files or Information Unix Shell Defense Evasion Execution Splunk Enterprise Splunk Enterprise Security Splunk Cloud Endpoint

Try in Splunk Security Cloud{: .btn .btn--success}

Description

The following analytic identifies base64 being decoded and passed to a Linux shell.

• Type: TTP
• Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
• Datamodel: Endpoint
• Last Updated: 2022-07-27
• Author: Michael Haag, Splunk
• ID: 637b603e-1799-40fd-bf87-47ecbd551b66

Annotations

ATT&CK

ID	Technique	Tactic
T1027	Obfuscated Files or Information	Defense Evasion

| T1059.004 | Unix Shell | Execution |

Kill Chain Phase

• Delivery
• Exploitation

NIST

• DE.CM

CIS20

• CIS 3
• CIS 5
• CIS 16

CVE

Search

| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Endpoint.Processes where Processes.process IN ("*base64 -d*","*base64 --decode*") AND Processes.process="*
|*" `linux_shells` by Processes.dest Processes.user Processes.parent_process_name Processes.process_name Processes.process Processes.process_id Processes.parent_process_id 
| `drop_dm_object_name(Processes)` 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| `linux_decode_base64_to_shell_filter`

Macros

The SPL above uses the following Macros:

• security_content_ctime
• security_content_summariesonly
• linux_shells

ℹ️ linux_decode_base64_to_shell_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Required field

• _time
• Processes.dest
• Processes.user
• Processes.parent_process_name
• Processes.parent_process
• Processes.original_file_name
• Processes.process_name
• Processes.process
• Processes.process_id
• Processes.parent_process_path
• Processes.process_path
• Processes.parent_process_id

How To Implement

To successfully implement this search you need to be ingesting information on process that include the name of the process responsible for the changes from your endpoints into the Endpoint datamodel in the Processes node. In addition, confirm the latest CIM App 4.20 or higher is installed and the latest TA for the endpoint product.

Known False Positives

False positives may be present based on legitimate software being utilized. Filter as needed.

Associated Analytic story

• Linux Living Off The Land

RBA

Risk Score	Impact	Confidence	Message
25.0	50	50	An instance of parent_process_name spawning process_name was identified on endpoint dest by user user decoding base64 and passing it to a shell.

ℹ️ The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

Reference

• https://github.com/redcanaryco/atomic-red-team/blob/master/atomics/T1027/T1027.md#atomic-test-1---decode-base64-data-into-script
• https://redcanary.com/blog/lateral-movement-with-secure-shell/
• https://linux.die.net/man/1/base64

Test Dataset

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

• https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1027/atomic_red_team/linux-sysmon.log

source | version: 1