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High Frequency of EC2 Multi-Region DescribeInstances API Calls

Metadata

  • Author: Elastic

  • Description: This hunting query identifies when a user makes multiple DescribeInstances API calls in multiple regions within a 30-second window. The DescribeInstances API call retrieves information about one or more EC2 instances in a region. High frequency of DescribeInstances API calls across multiple regions may indicate an adversary attempting to discover the EC2 instances in the account or perform reconnaissance on the EC2 environment.

  • UUID: e6e78858-6482-11ef-93bd-f661ea17fbcc

  • Integration: aws.cloudtrail

  • Language: [ES|QL]

  • Source File: High Frequency of EC2 Multi-Region DescribeInstances API Calls

Query

from logs-aws.cloudtrail-*
| where @timestamp > now() - 7 day

// 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)

// 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

Notes

  • Use the aws.cloudtrail.user_identity.arn field to identify the user making the requests and their role permissions
  • Use the cloud.region field to identify the regions where the DescribeInstances API calls were made
  • If leveraging SSM, query for StartSession API calls to determine if the user is attempting to establish a session with the EC2 instances
  • Filter for event.provider is ec2.amazonaws.com to pivot on unusual activity related to EC2 instances

MITRE ATT&CK Techniques

License

  • Elastic License v2