Profile Applicability:

  • Level 1

Description:

Amazon Cognito User Pools manage user authentication and provide the infrastructure to sign up, sign in, and manage users for applications. A user existence error occurs when a sign-up or sign-in attempt is made with an email or username that already exists in the pool, causing a potential security issue. By default, Amazon Cognito may return an error that discloses the existence of a user, which could be used by an attacker to gather information about the user base. Enabling the Prevent User Existence Errors option ensures that Cognito pools do not leak user existence information, thereby enhancing security.

Rationale:

  • Security: Preventing user existence errors helps reduce the risk of attackers using brute force or enumeration techniques to discover valid user accounts.

  • Compliance: Many security frameworks require user authentication systems to protect user information and avoid unintentionally exposing account data.

  • Best Practices: Hiding existence errors is a security best practice, making it harder for attackers to determine valid usernames or email addresses.

Impact:

Pros:

  • Enhanced Security: Preventing user existence errors improves the security of user accounts by not revealing if an account exists or not.

  • Reduction in Brute-Force Attacks: Reduces the ability of attackers to use brute force or other methods to enumerate valid users.

  • Compliance: Helps meet security requirements for user privacy, especially in industries where data exposure is heavily regulated.

Cons:

  • User Experience: There may be minor UX impacts, as users will no longer receive immediate feedback on whether their email/username already exists. However, this should be balanced with the need for stronger security.

  • Troubleshooting: Diagnosing issues where a user can't sign in may become harder, as you won't be able to directly identify if the account exists or is just incorrect credentials.

Default Value:

By default, Cognito User Pools do not prevent user existence errors. The feature must be explicitly enabled to enhance security.

Pre-requisite:

  • AWS IAM Permissions:

    • cognito-idp:DescribeUserPool

    • cognito-idp:UpdateUserPool

  • AWS CLI installed and configured.

  • Cognito User Pool created and operational.

Test Plan:

Using AWS Console:

  1. Sign in to the AWS Management Console.

  2. Navigate to Amazon Cognito under Services.

  3. Select User Pools and choose the user pool to check.

  4. Under General settings, select User pool settings.

  5. Check the Prevent user existence errors option.

    • If enabled, it will prevent revealing user existence errors during sign-in and sign-up attempts.

  6. If the option is not enabled, follow the Implementation Steps below to enable it.

Using AWS CLI:

  1. To describe the Cognito user pool and check the Prevent user existence errors setting, run:

    aws cognito-idp describe-user-pool --user-pool-id <user-pool-id> --query 'UserPool.UserPoolAddOns.UserExistenceError'

  2. If the output shows true, the feature is enabled. If it shows false, the feature is disabled.

Implementation Steps:

Using AWS Console:

  1. Sign in to the AWS Management Console and navigate to Amazon Cognito.

  2. In the Cognito Console, select User Pools and choose the user pool you want to update.

  3. Under General settings, select User pool settings.

  4. Enable the Prevent user existence errors option.

  5. Save the changes to enforce the updated security setting.

Using AWS CLI:

  1. To enable Prevent User Existence Errors, run the following command:

    aws cognito-idp update-user-pool --user-pool-id <user-pool-id> --user-pool-add-ons '{"UserExistenceError": true}'

  2. Verify the change by running:

    aws cognito-idp describe-user-pool --user-pool-id <user-pool-id> --query 'UserPool.UserPoolAddOns.UserExistenceError'

Backout Plan:

Using AWS Console:

  1. If enabling user existence error prevention causes issues, sign in to the AWS Management Console.

  2. Navigate to Amazon Cognito and select the User Pool.

  3. Under General Settings, go to Policies.

  4. Disable the Prevent User Existence Errors option.

  5. Save the changes.

Using AWS CLI:

  1. To disable user existence error prevention for a User Pool, run the following command:

    aws cognito-idp update-user-pool --user-pool-id <USER_POOL_ID> --user-existence-prevention DISABLED --region <REGION>

  2. Verify that the setting has been reverted by describing the User Pool again:

    aws cognito-idp describe-user-pool --user-pool-id <USER_POOL_ID> --region <REGION>

References:

CIS Controls Mapping:

Version

Control ID

Control Description

IG1

IG2

IG3

v8

3.4

Encrypt Data on End-User Devices – Ensure data encryption during file system access.

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●

●

v8

6.7

Implement Application Layer Filtering and Content Control – Ensure appropriate content filtering is applied to sensitive files.

●

●

●

v8

6.8

Define and Maintain Role-Based Access Control – Implement and manage role-based access for file systems.

●

●

●

v8

14.6

Protect Information Through Access Control Lists – Apply strict access control to file systems.

●

●

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