Detection: Detect SNICat SNI Exfiltration

EXPERIMENTAL DETECTION

This detection status is set to experimental. The Splunk Threat Research team has not yet fully tested, simulated, or built comprehensive datasets for this detection. As such, this analytic is not officially supported. If you have any questions or concerns, please reach out to us at research@splunk.com.

Updated Date: 2024-05-21 ID: 82d06410-134c-11eb-adc1-0242ac120002 Author: Shannon Davis, Splunk Type: TTP Product: Splunk Enterprise Security

Description

The following analytic identifies the use of SNICat tool commands within the TLS SNI field, indicating potential data exfiltration attempts. It leverages Zeek SSL data to detect specific SNICat commands such as LIST, LS, SIZE, LD, CB, EX, ALIVE, EXIT, WHERE, and finito in the server_name field. This activity is significant as SNICat is a known tool for covert data exfiltration using TLS. If confirmed malicious, this could allow attackers to exfiltrate sensitive data undetected, posing a severe threat to data confidentiality and integrity.

Search

 1`zeek_ssl` 
 2| rex field=server_name "(?<snicat>(LIST
 3|LS
 4|SIZE
 5|LD
 6|CB
 7|CD
 8|EX
 9|ALIVE
10|EXIT
11|WHERE
12|finito)-[A-Za-z0-9]{16}\.)" 
13| stats count by src_ip dest_ip server_name snicat 
14| where count>0 
15| table src_ip dest_ip server_name snicat 
16| `detect_snicat_sni_exfiltration_filter`

Data Source

Name	Platform	Sourcetype	Source	Supported App
N/A	N/A	N/A	N/A	N/A

Macros Used

Name	Value
zeek_ssl	`index=zeek sourcetype="zeek:ssl:json"`
detect_snicat_sni_exfiltration_filter	`search *`

detect_snicat_sni_exfiltration_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
T1041	Exfiltration Over C2 Channel	Exfiltration

KillChainPhase.ACTIONS_ON_OBJECTIVES

NistCategory.DE_CM

Cis18Value.CIS_13

APT3

APT32

APT39

Chimera

Confucius

GALLIUM

Gamaredon Group

Higaisa

Ke3chang

Kimsuky

Lazarus Group

Leviathan

LuminousMoth

MuddyWater

Sandworm Team

Stealth Falcon

Wizard Spider

ZIRCONIUM

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

You must be ingesting Zeek SSL data into Splunk. Zeek data should also be getting ingested in JSON format. We are detecting when any of the predefined SNICat commands are found within the server_name (SNI) field. These commands are LIST, LS, SIZE, LD, CB, EX, ALIVE, EXIT, WHERE, and finito. You can go further once this has been detected, and run other searches to decode the SNI data to prove or disprove if any data exfiltration has taken place.

Known False Positives

Unknown

Associated Analytic Story

Data Exfiltration

Risk Based Analytics (RBA)

Risk Message	Risk Score	Impact	Confidence
tbd	25	50	50

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

References

Detection Testing

Test Type	Status	Dataset	Source	Sourcetype
Validation	Not Applicable	N/A	N/A	N/A
Unit	❌ Failing	N/A	`N/A`	`N/A`
Integration	❌ Failing	N/A	`N/A`	`N/A`

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: 2