How will you restrict access of a user who has the private key of an EC2 server?

A compromised EC2 private key is a critical security incident that demands immediate action and long-term safeguards. This guide provides a deep dive into mitigating risks, hardening your environment, and adopting advanced strategies to prevent future breaches. We’ll cover technical steps, real-world examples, and AWS-native tools to secure your infrastructure.

Table of Contents

1. Immediate Response: Contain the Damage

   • Revoke the Key & Replace the Instance
   • Audit Active Sessions and Keys

2. Network Layer Restrictions

   • Security Groups: IP Whitelisting & Port Rules
   • NACLs: Subnet-Level Firewalls
   • VPNs, Bastion Hosts, and VPC Peering

3. IAM & Identity Hardening

   • Enforce MFA for SSH/RDP Access
   • Least Privilege IAM Policies
   • AWS Systems Manager (SSM) Session Manager

4. SSH/RDP Configuration Hardening

   • Disable Password Logins
   • Restrict Users & Commands
   • SSH Certificates vs. Static Keys

5. OS-Level Security

   • User Permissions & Sudoers File
   • File Integrity Monitoring (FIM)

6. Monitoring & Incident Response

   • AWS CloudTrail, GuardDuty, and CloudWatch
   • OS Logs and Fail2ban

7. Long-Term Strategies

   • Key Rotation & Automation
   • Zero-Trust Architectures
   • Third-Party Tools (HashiCorp Vault, Teleport)

8. Advanced Scenarios

• IMDSv2 for SSRF Protection
• Cross-Account Access Mitigation

Read more »