ID | Technique | Tactic |
---|---|---|
T1071.002 | File Transfer Protocols | Command And Control |
T1071 | Application Layer Protocol | Command And Control |
Detection: Detect Outbound SMB Traffic
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.
Description
The following analytic detects outbound SMB (Server Message Block) connections from internal hosts to external servers. It identifies this activity by monitoring network traffic for SMB requests directed towards the Internet, which are unusual for standard operations. This detection is significant for a SOC as it can indicate an attacker's attempt to retrieve credential hashes through compromised servers, a key step in lateral movement and privilege escalation. If confirmed malicious, this activity could lead to unauthorized access to sensitive data and potential full system compromise.
Search
1
2| tstats `security_content_summariesonly` earliest(_time) as start_time latest(_time) as end_time values(All_Traffic.action) as action values(All_Traffic.app) as app values(All_Traffic.dest_ip) as dest_ip values(All_Traffic.dest_port) as dest_port values(sourcetype) as sourcetype count from datamodel=Network_Traffic where (All_Traffic.action=allowed All_Traffic.direction=outbound All_Traffic.dest_port=139 OR All_Traffic.dest_port=445 OR All_Traffic.app="smb") by All_Traffic.src_ip
3| `drop_dm_object_name("All_Traffic")`
4| eval match=case( cidrmatch("10.0.0.0/8" ,dest_ip) ,"1", cidrmatch("172.16.0.0/12" ,dest_ip) ,"1", cidrmatch("192.168.0.0/16" ,dest_ip) ,"1", cidrmatch("100.64.0.0/10" ,dest_ip) ,"1", 1=1,"0")
5| search match=0
6| fields - match
7| `security_content_ctime(start_time)`
8| `security_content_ctime(end_time)`
9| `detect_outbound_smb_traffic_filter`
Data Source
Name | Platform | Sourcetype | Source | Supported App |
---|---|---|---|---|
N/A | N/A | N/A | N/A | N/A |
Macros Used
Name | Value |
---|---|
security_content_ctime | convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$) |
detect_outbound_smb_traffic_filter | search * |
detect_outbound_smb_traffic_filter
is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.
Annotations
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 |
Implementation
This search also requires you to be ingesting your network traffic and populating the Network_Traffic data model
Known False Positives
It is likely that the outbound Server Message Block (SMB) traffic is legitimate, if the company's internal networks are not well-defined in the Assets and Identity Framework. Categorize the internal CIDR blocks as internal
in the lookup file to avoid creating notable events for traffic destined to those CIDR blocks. Any other network connection that is going out to the Internet should be investigated and blocked. Best practices suggest preventing external communications of all SMB versions and related protocols at the network boundary.
Associated Analytic Story
Risk Based Analytics (RBA)
Risk Message | Risk Score | Impact | Confidence |
---|---|---|---|
An outbound SMB connection from $src_ip$ in your infrastructure connecting to dest ip $dest_ip$ | 25 | 50 | 50 |
Detection Testing
Test Type | Status | Dataset | Source | Sourcetype |
---|---|---|---|---|
Validation | Not Applicable | N/A | N/A | N/A |
Unit | ✅ Passing | Dataset | conn.log |
bro:conn:json |
Integration | ✅ Passing | Dataset | conn.log |
bro:conn:json |
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: 5