detection-rules
Loading

AWS WAF Access Control List Deletion

Identifies the deletion of an AWS Web Application Firewall (WAF) Web ACL. Web ACLs are the core enforcement objects in AWS WAF, defining which traffic is inspected, allowed, or blocked for protected applications. Deleting a Web ACL removes all associated rules, protections, and logging configurations. Adversaries who obtain sufficient privileges may delete a Web ACL to disable critical security controls, evade detection, or prepare for downstream attacks such as web-application compromise, data theft, or resource abuse. Because Web ACLs are rarely deleted outside of controlled maintenance or infrastructure updates, unexpected deletions may indicate potential defense evasion.

Rule type: query
Rule indices:

  • filebeat-*
  • logs-aws.cloudtrail-*

Rule Severity: medium
Risk Score: 47
Runs every:
Searches indices from: now-6m
Maximum alerts per execution: ?
References:

Tags:

  • Domain: Cloud
  • Data Source: AWS
  • Data Source: Amazon Web Services
  • Data Source: AWS WAF
  • Use Case: Network Security Monitoring
  • Tactic: Defense Evasion
  • Resources: Investigation Guide

Version: ?
Rule authors:

  • Elastic

Rule license: Elastic License v2

Disclaimer: This investigation guide was created using generative AI technology and has been reviewed to improve its accuracy and relevance. While every effort has been made to ensure its quality, validate and adapt it to suit your operational needs.

AWS Web Application Firewall (WAF) protects applications by inspecting HTTP/S traffic and applying rule groups, managed rule sets, and custom logic to block or allow requests. A Web ACL is the primary enforcement object that binds these protections to CloudFront distributions, Application Load Balancers, API Gateway stages, and AppSync APIs.

Deleting a Web ACL immediately removes all protections and logging associated with that application entry point. Because this action can expose applications to direct exploitation, adversaries may delete Web ACLs to disable defenses, evade detection, or prepare for lateral movement or data exfiltration.

This rule detects successful DeleteWebACL events across WAF Classic, WAF Regional, and WAFv2 APIs.

  • Identify the actor and access context

    • Review aws.cloudtrail.user_identity.arn and access_key_id for the identity that initiated deletion.
    • Determine whether this principal normally manages WAF resources.
    • Check if the call originated via IAM role assumption, federated identity, or long-lived IAM key.

  • Assess the deleted ACL

    • Check aws.cloudtrail.request_parameters for:
      • The Web ACL ID (WebACLId, Id, or ARN).
      • The scope (REGIONAL vs. CLOUDFRONT).
      • Associated resource ARNs that were protected.
    • Determine which applications or APIs depended on this Web ACL.
    • Evaluate the criticality and sensitivity of any exposed endpoints.

  • Correlate with related security-affecting activity

    • Use CloudTrail to pivot on:
      • The same identity (user_identity.arn or access key).
      • The same application load balancer, CloudFront distribution, or API Gateway stage.
    • Look for:
      • Prior rule updates (UpdateWebACL, DeleteRuleGroup, etc.).
      • IAM privilege escalation events.
      • Changes to logging or monitoring (e.g., disabling WAF logging).

  • Investigate request origin and tooling

    • Review source.ip, ASN, and geo-location for anomalies.
    • Analyze user_agent.original to identify automation, custom scripts, CLI usage, or console access.

  • Evaluate operational context

    • Determine whether the deletion aligns with:
      • Scheduled maintenance.
      • IaC-driven redeployments (Terraform, CDK, CloudFormation).
      • Known migrations between WAF Classic and WAFv2.
    • If deletion occurred outside expected time windows or without a corresponding change ticket, treat it as suspicious.

  • Expected infrastructure lifecycle events

    • IaC pipelines may destroy and recreate Web ACLs as part of environment rotation or blue/green deployments.
    • Confirm whether the deleting identity matches known automation roles.

  • Planned refactoring or migrations

    • Organizations transitioning to WAFv2 or moving resources across regions may intentionally delete legacy ACLs.

  • Testing and sandbox environments

    • Developers may frequently create and remove ACLs during experimentation.
    • Tune the rule to suppress events from non-production accounts or specific tags.

  • Automated cleanup

    • Certain CI/CD processes or teardown scripts remove WAF resources during ephemeral environment shutdowns.

If any deletion is inconsistent with normal operational patterns or performed by an unexpected principal, treat it as a potential defense-evasion attempt.

  • Containment

    • Immediately assess exposed applications. If feasible, apply temporary restrictive network controls (e.g., ALB security group tightening or CloudFront WAFv2 fallback rules).
    • Revoke session tokens or access keys associated with suspicious actors.

  • Restore protections

    • Recreate the deleted Web ACL using IaC definitions, backups, or previous configurations.
    • Validate that logging and monitoring (WAF logs, CloudWatch alarms, SIEM ingestion) are correctly restored.

  • Scope and impact analysis

    • Review CloudTrail for follow-on or preceding activity by the same actor:
      • Rule modifications.
      • IAM policy changes.
      • Application configuration updates.
      • API Gateway or ALB changes.
    • Review application access logs for unusual requests following ACL removal.

  • Hardening

    • Limit IAM permissions for waf:DeleteWebACL, wafv2:DeleteWebACL, and related actions to a small set of trusted roles.
    • Enforce MFA for administrative access.
    • Use AWS Config or Security Hub controls to detect unauthorized modifications to WAF resources.

  • Post-incident improvements

    • Update change-management workflows to include required approvals for WAF modifications.
    • Improve monitoring for other defense-evasion patterns such as disabling GuardDuty, CloudTrail, or logging.
event.dataset: aws.cloudtrail
    and event.provider: (waf.amazonaws.com or waf-regional.amazonaws.com or wafv2.amazonaws.com)
    and event.action: DeleteWebACL
    and event.outcome: success

Framework: MITRE ATT&CK