Detection: Detect Spike in blocked Outbound Traffic from your AWS

Description

The following analytic identifies spikes in blocked outbound network connections originating from within your AWS environment. It leverages VPC Flow Logs data from CloudWatch, focusing on blocked actions from internal IP ranges to external destinations. This detection is significant as it can indicate potential exfiltration attempts or misconfigurations leading to data leakage. If confirmed malicious, such activity could allow attackers to bypass network defenses, leading to unauthorized data transfer or communication with malicious external entities.

Search

 1`cloudwatchlogs_vpcflow` action=blocked (src_ip=10.0.0.0/8 OR src_ip=172.16.0.0/12 OR src_ip=192.168.0.0/16) ( dest_ip!=10.0.0.0/8 AND dest_ip!=172.16.0.0/12 AND dest_ip!=192.168.0.0/16)  [search  `cloudwatchlogs_vpcflow` action=blocked (src_ip=10.0.0.0/8 OR src_ip=172.16.0.0/12 OR src_ip=192.168.0.0/16) ( dest_ip!=10.0.0.0/8 AND dest_ip!=172.16.0.0/12 AND dest_ip!=192.168.0.0/16)  
 2| stats count as numberOfBlockedConnections by src_ip 
 3| inputlookup baseline_blocked_outbound_connections append=t 
 4| fields - latestCount 
 5| stats values(*) as * by src_ip 
 6| rename numberOfBlockedConnections as latestCount 
 7| eval newAvgBlockedConnections=avgBlockedConnections + (latestCount-avgBlockedConnections)/720 
 8| eval newStdevBlockedConnections=sqrt(((pow(stdevBlockedConnections, 2)*719 + (latestCount-newAvgBlockedConnections)*(latestCount-avgBlockedConnections))/720)) 
 9| eval avgBlockedConnections=coalesce(newAvgBlockedConnections, avgBlockedConnections), stdevBlockedConnections=coalesce(newStdevBlockedConnections, stdevBlockedConnections), numDataPoints=if(isnull(latestCount), numDataPoints, numDataPoints+1) 
10| table src_ip, latestCount, numDataPoints, avgBlockedConnections, stdevBlockedConnections 
11| outputlookup baseline_blocked_outbound_connections 
12| eval dataPointThreshold = 5, deviationThreshold = 3 
13| eval isSpike=if((latestCount > avgBlockedConnections+deviationThreshold*stdevBlockedConnections) AND numDataPoints > dataPointThreshold, 1, 0) 
14| where isSpike=1 
15| table src_ip] 
16| stats values(dest_ip) as dest_ip, values(interface_id) as "resourceId" count as numberOfBlockedConnections, dc(dest_ip) as uniqueDestConnections by src_ip 
17| `detect_spike_in_blocked_outbound_traffic_from_your_aws_filter`

Data Source

Macros Used

Annotations

Default Configuration

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

Implementation

You must install the AWS App for Splunk (version 5.1.0 or later) and Splunk Add-on for AWS (version 4.4.0 or later), then configure your VPC Flow logs. You can modify dataPointThreshold and deviationThreshold to better fit your environment. The dataPointThreshold variable is the number of data points required to meet the definition of "spike." The deviationThreshold variable is the number of standard deviations away from the mean that the value must be to be considered a spike. This search works best when you run the "Baseline of Blocked Outbound Connection" support search once to create a history of previously seen blocked outbound connections.

Known False Positives

The false-positive rate may vary based on the values ofdataPointThreshold and deviationThreshold. Additionally, false positives may result when AWS administrators roll out policies enforcing network blocks, causing sudden increases in the number of blocked outbound connections.

Associated Analytic Story

• AWS Network ACL Activity

• Command And Control

• Suspicious AWS Traffic

Risk Based Analytics (RBA)

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: 2