Cis AWS Compute 3.5

Ensure 'readonlyRootFilesystem' is set to 'true' for Amazon ECS task definitions

Description

Ensure the readonlyRootFilesystem parameter is enabled in Amazon ECS task definitions to restrict write access to the filesystem.

Note: This recommendation assumes that only the latest active revision of a task definition is in use. If older revisions are in use, apply the audit and remediation procedures to those revisions as needed.

Rationale

Enabling readonlyRootFilesystem minimizes security risks by ensuring the container's filesystem cannot be altered unless specific read-write permissions are granted.

Impact

There may be some administrative effort required to ensure Amazon ECS applications function as expected with a read-only root filesystem. Applications that need to write to the filesystem will require volume mounts or tmpfs mounts.

Audit Procedure

Using AWS Console

1. Login to the ECS console using https://console.aws.amazon.com/ecs/.
2. In the left panel, click Task definitions.
3. Click the name of a task definition.
4. Click on the latest active revision of the task definition.
5. Click JSON.
6. For each element under containerDefinitions, ensure readonlyRootFilesystem is set to true.
7. Repeat steps 1-6 for each task definition.

Using AWS CLI

Run the following command to list task definitions:

aws ecs list-task-definitions

For the latest revision of a task definition, run the following command:

aws ecs describe-task-definition --task-definition <task-definition-arn> --query 'taskDefinition.containerDefinitions[*].readonlyRootFilesystem'

Ensure that the command returns only true. Repeat for each task definition.

Expected Result

The readonlyRootFilesystem parameter should be set to true for all containers in all task definitions.

Remediation

Using AWS Console

1. Login to the ECS console using https://console.aws.amazon.com/ecs/.
2. In the left panel, click Task definitions.
3. Click the name of a task definition.
4. Click on the latest active revision of the task definition.
5. Click Create new revision.
6. Click Create new revision with JSON.
7. For each element under containerDefinitions, set readonlyRootFilesystem to true.
8. Click Create.
9. Repeat steps 1-8 for each task definition requiring remediation.

Note: When a task definition is updated, running tasks launched from the previous task definition remain unchanged. Updating a running task requires redeploying it with the new task definition.

Using AWS CLI

No specific CLI remediation provided. Register a new task definition revision with corrected readonlyRootFilesystem setting using aws ecs register-task-definition.

Default Value

By default, readonlyRootFilesystem is set to false.

References

1. https://docs.aws.amazon.com/AmazonECS/latest/developerguide/task_definition_parameters.html
2. https://awscli.amazonaws.com/v2/documentation/api/latest/reference/ecs/list-task-definitions.html
3. https://awscli.amazonaws.com/v2/documentation/api/latest/reference/ecs/describe-task-definition.html

CIS Controls

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Level 1 | Automated