Profile Applicability:

  • Level 1

Description:

This control ensures that no sensitive information such as passwords, API keys, access tokens, or private keys is stored in Amazon EC2 User Data. User Data scripts are commonly used to automate instance configuration during launch, but any plaintext secrets embedded in them are accessible to users with permissions to describe or view instance metadata, leading to potential data exposure and security breaches. 

Rationale:

EC2 User Data is stored in instance metadata and can be retrieved through the AWS Management Console, CLI, or API. If sensitive credentials or configurations are placed in plaintext within User Data, any compromised IAM user or EC2 role with read access can extract and misuse this data. Storing secrets securely in AWS Secrets Manager, AWS Systems Manager Parameter Store (with encryption), or similar secret management systems ensures that sensitive data is encrypted, controlled, and auditable. 

Impact:

  • Positive Impact: Improves data security by preventing unintentional exposure of sensitive information, ensuring compliance with least-privilege and data protection principles.

  • Negative Impact: Scripts requiring secret values must be refactored to fetch secrets securely at runtime using IAM roles and authorized secret management services. 

Default Value:

AWS does not automatically scan or prevent the inclusion of secrets in EC2 User Data; this must be implemented manually or through automated auditing tools. 

Pre-Requisite:

  • IAM permissions required: ec2:DescribeInstances, ec2:DescribeInstanceAttribute.
  • A defined list of sensitive patterns (e.g., “password=”, “AWS_ACCESS_KEY_ID”, “SECRET_KEY”, “token=”, “PRIVATE_KEY”).

Remediation:

Test Plan 

Using AWS Console:

  1. Sign in to the AWS Management Console.

  2. Navigate to EC2 → Instances.

  3. Select an instance → Actions → Instance settings → View/Change User Data.

  4. Review the displayed script for sensitive information such as credentials, tokens, or private keys.

  5. If secrets are present in plaintext, the instance is non-compliant.

Implementation Plan 

Using AWS Console:

  1. Identify all EC2 instances with non-compliant User Data.
  2. Copy and review their startup scripts.
  3. Remove any sensitive information such as passwords, access tokens, or keys.
  4. Store these secrets securely using:

    • AWS Secrets Manager (recommended for credentials and API keys).

    • AWS Systems Manager Parameter Store (with KMS encryption).

  5. Update User Data scripts to securely retrieve secrets at runtime via IAM roles. 
  6. Re-launch the instances with sanitized User Data.


Backout Plan:

Using AWS Console:

  1. If User Data removal disrupts startup processes, temporarily use environment variables or configuration files stored in encrypted EBS volumes while implementing a permanent secret management solution.
  2. Maintain versioned backups of sanitized scripts for rollback if required.

References: