| ID | Technique | Tactic |
|---|
Detection: Detect Spike in blocked Outbound Traffic from your AWS
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 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
No data sources specified for this detection.
Macros Used
| Name | Value |
|---|---|
| cloudwatchlogs_vpcflow | sourcetype=aws:cloudwatchlogs:vpcflow |
| detect_spike_in_blocked_outbound_traffic_from_your_aws_filter | search * |
detect_spike_in_blocked_outbound_traffic_from_your_aws_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
NistCategory.DE_AE
Cis18Value.CIS_13
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 Risk Event | True |
This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.
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
Risk Based Analytics (RBA)
| Risk Message | Risk Score | Impact | Confidence |
|---|---|---|---|
| Blocked outbound traffic from your AWS | 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.
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: 3