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Potential AWS S3 Bucket Ransomware Note Uploaded

Identifies potential ransomware note being uploaded to an AWS S3 bucket. This rule detects the PutObject S3 API call with a common ransomware note file extension such as .ransom, or .lock. Adversaries with access to a misconfigured S3 bucket may retrieve, delete, and replace objects with ransom notes to extort victims.

Rule type: esql
Rule indices:

Rule Severity: medium
Risk Score: 47
Runs every:
Searches indices from: now-9m
Maximum alerts per execution: ?
References:

Tags:

  • Domain: Cloud
  • Data Source: AWS
  • Data Source: Amazon Web Services
  • Data Source: AWS S3
  • Use Case: Threat Detection
  • Tactic: Impact
  • Resources: Investigation Guide

Version: ?
Rule authors:

  • Elastic

Rule license: Elastic License v2
AWS S3 data types need to be enabled in the CloudTrail trail configuration.

This rule detects the PutObject S3 API call with a common ransomware note file extension such as .ransom, or .lock. Adversaries with access to a misconfigured S3 bucket may retrieve, delete, and replace objects with ransom notes to extort victims.

  • Identify the Actor: Review the aws.cloudtrail.user_identity.arn and aws.cloudtrail.user_identity.access_key_id fields to identify who performed the action. Verify if this actor typically performs such actions and if they have the necessary permissions.
  • Review the Request Details: Examine the aws.cloudtrail.request_parameters to understand the specific details of the PutObject action. Look for any unusual parameters that could suggest unauthorized or malicious modifications.
  • Analyze the Source of the Request: Investigate the source.ip and source.geo fields to determine the geographical origin of the request. An external or unexpected location might indicate compromised credentials or unauthorized access.
  • Contextualize with Timestamp: Use the @timestamp field to check when the ransom note was uploaded. Changes during non-business hours or outside regular maintenance windows might require further scrutiny.
  • Inspect the Ransom Note: Review the aws.cloudtrail.request_parameters for the PutObject action to identify the characteristics of the uploaded ransom note. Look for common ransomware file extensions such as .txt, .note, .ransom, or .html.
  • Correlate with Other Activities: Search for related CloudTrail events before and after this action to see if the same actor or IP address engaged in other potentially suspicious activities.
  • Check for Object Deletion or Access: Look for DeleteObject, DeleteObjects, or GetObject API calls to the same S3 bucket that may indicate the adversary accessing and destroying objects before placing the ransom note.
  • Legitimate Administrative Actions: Confirm if the PutObject action aligns with scheduled updates, maintenance activities, or legitimate administrative tasks documented in change management systems.
  • Consistency Check: Compare the action against historical data of similar activities performed by the user or within the organization. If the action is consistent with past legitimate activities, it might indicate a false alarm.
  • Verify through Outcomes: Check the aws.cloudtrail.response_elements and the event.outcome to confirm if the upload was successful and intended according to policy.
  • Immediate Review and Reversal if Necessary: If the activity was unauthorized, remove the uploaded ransom notes from the S3 bucket and review the bucket's access logs for any suspicious activity.
  • Enhance Monitoring and Alerts: Adjust monitoring systems to alert on similar PutObject actions, especially those involving sensitive data or unusual file extensions.
  • Educate and Train: Provide additional training to users with administrative rights on the importance of security best practices concerning S3 bucket management and the risks of ransomware.
  • Audit S3 Bucket Policies and Permissions: Conduct a comprehensive audit of all S3 bucket policies and associated permissions to ensure they adhere to the principle of least privilege.
  • Incident Response: If there's an indication of malicious intent or a security breach, initiate the incident response protocol to mitigate any damage and prevent future occurrences.

For further guidance on managing S3 bucket security and protecting against ransomware, refer to the AWS S3 documentation and AWS best practices for security. Additionally, consult the following resources for specific details on S3 ransomware protection:

from logs-aws.cloudtrail-*

// any successful uploads via S3 API requests
| where
  event.dataset == "aws.cloudtrail"
  and event.provider == "s3.amazonaws.com"
  and event.action == "PutObject"
  and event.outcome == "success"

// extract object key from API request parameters
| dissect aws.cloudtrail.request_parameters "%{?ignore_values}key=%{Esql.aws_cloudtrail_request_parameters_object_key}}"

// regex match against common ransomware naming patterns
| where
  Esql.aws_cloudtrail_request_parameters_object_key rlike "(.*)(ransom|lock|crypt|enc|readme|how_to_decrypt|decrypt_instructions|recovery|datarescue)(.*)"
  and not Esql.aws_cloudtrail_request_parameters_object_key rlike "(.*)(AWSLogs|CloudTrail|access-logs)(.*)"

// keep relevant ECS and derived fields
| keep
  tls.client.server_name,
  aws.cloudtrail.user_identity.arn,
  Esql.aws_cloudtrail_request_parameters_object_key

// aggregate by server name, actor, and object key
| stats
    Esql.event_count = count(*)
  by
    tls.client.server_name,
    aws.cloudtrail.user_identity.arn,
    Esql.aws_cloudtrail_request_parameters_object_key

// filter for rare single uploads (likely test/detonation)
| where Esql.event_count == 1

Framework: MITRE ATT&CK