AWS EC2 Multi-Region DescribeInstances API Calls

Identifies when a single AWS resource is making DescribeInstances API calls in more than 10 regions within a 30-second window. This could indicate a potential threat actor attempting to discover the AWS infrastructure across multiple regions using compromised credentials or a compromised instance. Adversaries may use this information to identify potential targets for further exploitation or to gain a better understanding of the target’s infrastructure.

Rule type: esql

Rule indices: None

Severity: low

Risk score: 21

Runs every: 5m

Searches indices from: now-9m (Date Math format, see also Additional look-back time)

Maximum alerts per execution: 100

References:

Tags:

Domain: Cloud
Data Source: AWS
Data Source: AWS EC2
Use Case: Threat Detection
Tactic: Discovery

Version: 2

Rule authors:

Elastic

Rule license: Elastic License v2

Rule query

edit

from logs-aws.cloudtrail-*

// filter for DescribeInstances API calls
| where event.dataset == "aws.cloudtrail" and event.provider == "ec2.amazonaws.com" and event.action == "DescribeInstances"

// truncate the timestamp to a 30-second window
| eval target_time_window = DATE_TRUNC(30 seconds, @timestamp)

// keep only the relevant fields
| keep target_time_window, aws.cloudtrail.user_identity.arn, cloud.region

// count the number of unique regions and total API calls within the 30-second window
| stats region_count = count_distinct(cloud.region), window_count = count(*) by target_time_window, aws.cloudtrail.user_identity.arn

// filter for resources making DescribeInstances API calls in more than 10 regions within the 30-second window
| where region_count >= 10 and window_count >= 10

// sort the results by time windows in descending order
| sort target_time_window desc

Framework: MITRE ATT&CK^TM

Tactic:
- Name: Discovery
- ID: TA0007
- Reference URL: https://attack.mitre.org/tactics/TA0007/
Technique:
- Name: Cloud Infrastructure Discovery
- ID: T1580
- Reference URL: https://attack.mitre.org/techniques/T1580/

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