​
Event Information

  • The EnableVpcClassicLink event in AWS for EC2 refers to the action of enabling ClassicLink for a VPC (Virtual Private Cloud).
  • ClassicLink allows EC2 instances in a VPC to communicate with instances in the EC2-Classic platform using private IP addresses, without requiring public IP addresses or NAT gateways.
  • Enabling VpcClassicLink event enables the ClassicLink feature for a specific VPC, allowing EC2 instances within that VPC to establish communication with EC2-Classic instances.

​
Examples

  • Increased attack surface: Enabling VPC ClassicLink for EC2 instances can potentially increase the attack surface as it allows communication between instances in a VPC and instances in the ClassicLink-enabled VPC. This means that an attacker who gains access to an instance in the ClassicLink-enabled VPC may be able to exploit vulnerabilities in instances within the VPC.

  • Lack of network isolation: ClassicLink allows EC2 instances in a VPC to communicate with instances in a ClassicLink-enabled VPC using private IP addresses. This can lead to a lack of network isolation, as instances in the ClassicLink-enabled VPC can potentially access resources within the VPC that they should not have access to.

  • Limited security controls: ClassicLink does not provide the same level of security controls as native VPC networking. For example, ClassicLink does not support security groups or network ACLs, which are important tools for controlling inbound and outbound traffic in a VPC. This can make it more difficult to enforce security policies and restrict access to resources within the VPC.

​
Remediation

​
Using Console

  1. Example 1: Unauthorized Access to AWS EC2 Instance

    • Step 1: Identify the unauthorized access event in the AWS CloudTrail logs or AWS Security Hub.
    • Step 2: Determine the source IP address or user account associated with the unauthorized access.
    • Step 3: Disable or remove the compromised user account or IAM role from the EC2 instance’s security group or IAM policies.
    • Step 4: Change the SSH key pair associated with the EC2 instance to prevent further unauthorized access.
    • Step 5: Enable AWS CloudTrail logging and configure alerts to be notified of any future unauthorized access attempts.

  2. Example 2: High CPU Utilization on AWS EC2 Instance

    • Step 1: Monitor the CPU utilization of the EC2 instance using Amazon CloudWatch metrics.
    • Step 2: Identify the process or application causing the high CPU utilization.
    • Step 3: Optimize the application or process to reduce CPU usage, such as optimizing code, improving database queries, or scaling horizontally.
    • Step 4: Consider resizing the EC2 instance to a higher instance type with more CPU resources if the high CPU utilization is persistent.
    • Step 5: Set up CloudWatch alarms to notify you when CPU utilization exceeds a certain threshold in the future.

  3. Example 3: Unencrypted EBS Volume in AWS EC2 Instance

    • Step 1: Identify the unencrypted EBS volume using AWS Config or AWS Security Hub.
    • Step 2: Create a snapshot of the unencrypted EBS volume as a backup.
    • Step 3: Copy the data from the unencrypted EBS volume to a new encrypted EBS volume.
    • Step 4: Detach the unencrypted EBS volume from the EC2 instance.
    • Step 5: Attach the newly created encrypted EBS volume to the EC2 instance and update any necessary configurations or mount points.

​
Using CLI

  1. Ensure that all EC2 instances are using the latest Amazon Machine Images (AMIs) by regularly checking for updates and patching any vulnerabilities. Use the following AWS CLI commands:

    • List all EC2 instances: aws ec2 describe-instances
    • Identify instances with outdated AMIs: aws ec2 describe-images --owners amazon --filters "Name=name,Values=amzn-ami-hvm-*" --query 'Images[*].[ImageId,CreationDate]' --output text | sort -k2 | tail -n 1
    • Update the AMI for the identified instances: aws ec2 create-image --instance-id <instance-id> --name "Updated AMI" --description "Updated AMI for security patching"
    • Terminate the old instance and launch a new instance using the updated AMI.

  2. Implement security groups and network ACLs to restrict inbound and outbound traffic to only necessary ports and protocols. Use the following AWS CLI commands:

    • List all security groups: aws ec2 describe-security-groups
    • Identify security groups with overly permissive rules: aws ec2 describe-security-groups --query 'SecurityGroups[?length(IpPermissions[?IpProtocol==\-1` || (IpProtocol==`tcp` && (ToPort==null || ToPort>65535)) || (IpProtocol==`udp` && (ToPort==null || ToPort>65535)) || (IpProtocol==`icmp` && (ToPort==null || ToPort>255)))])’`
    • Update the security group rules to allow only necessary traffic: aws ec2 revoke-security-group-ingress --group-id <security-group-id> --protocol <protocol> --port <port> --source <source-ip>
    • Repeat the above command for each unnecessary rule.

  3. Enable AWS CloudTrail to monitor and log all API activity within your AWS account. Use the following AWS CLI commands:

    • Create a new S3 bucket to store CloudTrail logs: aws s3api create-bucket --bucket <bucket-name> --region <region>
    • Enable CloudTrail for your AWS account: aws cloudtrail create-trail --name <trail-name> --s3-bucket-name <bucket-name> --is-multi-region-trail
    • Start logging API activity: aws cloudtrail start-logging --name <trail-name>
    • Verify that CloudTrail is enabled and logging: aws cloudtrail describe-trails --trail-name-list <trail-name>

​
Using Python

To remediate the issues mentioned in the previous response for AWS EC2 using Python, you can use the following approaches:

  1. Enforce encryption for EBS volumes:

    • Use the AWS SDK for Python (Boto3) to identify unencrypted EBS volumes.
    • Create a Python script that iterates through all EC2 instances and their attached volumes.
    • For each unencrypted volume, use the create_snapshot method to create a snapshot of the volume.
    • Use the copy_snapshot method to copy the snapshot and enable encryption during the copy process.
    • Once the encrypted snapshot is created, use the create_volume method to create a new encrypted volume.
    • Finally, detach the unencrypted volume and attach the newly created encrypted volume to the instance.

  2. Enable VPC flow logs:

    • Use Boto3 to check if VPC flow logs are enabled for each VPC.
    • Create a Python script that iterates through all VPCs and checks if flow logs are enabled.
    • If flow logs are not enabled, use the create_flow_logs method to enable them.
    • Specify the desired configuration, such as the destination S3 bucket, IAM role, and log format.

  3. Enable AWS Config:

    • Use Boto3 to check if AWS Config is enabled for the AWS account.
    • Create a Python script that checks the status of AWS Config.
    • If AWS Config is not enabled, use the put_configuration_recorder and put_delivery_channel methods to enable it.
    • Specify the desired configuration, such as the S3 bucket for storing configuration history and the IAM role for delivery channel.

Please note that the provided code snippets are simplified examples, and you may need to modify them based on your specific requirements and environment setup.