Least privilege principle in AWS - Mini Project: Build & Apply

Implementing Least Privilege Principle with AWS IAM Policy

📖 Scenario: You are working as a cloud administrator for a company. Your task is to create an AWS IAM policy that follows the least privilege principle. This means the policy should grant only the minimum permissions necessary for a user to list objects in a specific S3 bucket.

🎯 Goal: Create an AWS IAM policy JSON that allows listing objects only in the bucket named example-bucket. The policy should not allow any other actions or access to other buckets.

📋 What You'll Learn

Create a JSON dictionary named policy with the version set to 2012-10-17.

Add a statement list with one statement object.

The statement must have Effect set to Allow.

The statement must allow the action s3:ListBucket.

The statement must restrict the resource to the ARN of example-bucket only.

💡 Why This Matters

🌍 Real World

IAM policies are used to control access to AWS resources securely. Following the least privilege principle helps protect resources from accidental or malicious misuse.

💼 Career

Cloud administrators and security engineers regularly create and audit IAM policies to ensure users and services have only the permissions they need.

1

Create the base policy dictionary

Create a dictionary called policy with the key Version set to the string "2012-10-17".

AWS

# Create the base policy dictionary with Version key
# Your code here

Hint

The policy dictionary must have a key named Version with value "2012-10-17".

2

Add the statement list with one statement

Add a key Statement to the policy dictionary. Set it to a list containing one dictionary.

AWS

policy = {
    "Version": "2012-10-17"
}
# Add Statement key with a list containing one dictionary
# Your code here

Hint

The Statement key must be a list with one empty dictionary inside.

3

Define the statement with Effect, Action, and Resource

Inside the first dictionary in the Statement list, add the keys Effect, Action, and Resource. Set Effect to "Allow", Action to "s3:ListBucket", and Resource to the ARN string "arn:aws:s3:::example-bucket".

AWS

policy = {
    "Version": "2012-10-17",
    "Statement": [
        {}
    ]
}
# Add Effect, Action, and Resource keys inside the statement dictionary
# Your code here

Hint

Make sure the statement dictionary has exactly these keys and values to grant minimal permission.

4

Complete the policy with least privilege principle

Ensure the policy dictionary is complete and correctly formatted as a valid AWS IAM policy JSON that grants only s3:ListBucket permission on example-bucket.

AWS

policy = {
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": "s3:ListBucket",
            "Resource": "arn:aws:s3:::example-bucket"
        }
    ]
}
# Finalize the policy dictionary
# Your code here

Hint

Review the entire policy dictionary to confirm it grants only the required permission.

Practice

1. What does the least privilege principle mean in AWS security?

easy

A. Users get only the permissions they need to do their job

B. Users get full access to all AWS services

C. Users share passwords to access resources

D. Users can access resources without authentication

Solution

1. Step 1: Understand the principle meaning

   The least privilege principle means giving users only the minimum permissions they need.

2. Step 2: Compare options to principle

   Only Users get only the permissions they need to do their job matches this by limiting permissions to what is needed.

3. Final Answer:

   Users get only the permissions they need to do their job -> Option A

4. Quick Check:

   Least privilege = minimal needed access [OK]

Hint: Least privilege means minimum permissions needed [OK]

Common Mistakes:

• Thinking least privilege means full access
• Confusing least privilege with no access
• Assuming password sharing is secure

2. Which IAM policy snippet follows the least privilege principle for allowing S3 read-only access to a specific bucket my-bucket?

easy

A. {\"Effect\": \"Allow\", \"Action\": [\"s3:DeleteObject\"], \"Resource\": \"arn:aws:s3:::my-bucket/*\"}

B. {\"Effect\": \"Allow\", \"Action\": \"s3:*\", \"Resource\": \"*\"}

C. {\"Effect\": \"Allow\", \"Action\": [\"s3:GetObject\"], \"Resource\": \"arn:aws:s3:::my-bucket/*\"}

D. {\"Effect\": \"Allow\", \"Action\": [\"ec2:StartInstances\"], \"Resource\": \"*\"}

Solution

1. Step 1: Identify required permissions for read-only S3 access

   Read-only means allowing only s3:GetObject on the specific bucket's objects.

2. Step 2: Match policy actions and resources

   {\"Effect\": \"Allow\", \"Action\": [\"s3:GetObject\"], \"Resource\": \"arn:aws:s3:::my-bucket/*\"} allows only s3:GetObject on my-bucket objects, following least privilege.

3. Final Answer:

   Policy allowing only s3:GetObject on my-bucket objects -> Option C

4. Quick Check:

   Least privilege = specific action + resource [OK]

Hint: Allow only needed actions on specific resources [OK]

Common Mistakes:

• Using wildcard * for all actions or resources
• Allowing delete or write actions unnecessarily
• Granting permissions for unrelated services

3. Given this IAM policy snippet, what is the effective permission granted?

{
  "Effect": "Allow",
  "Action": ["s3:PutObject", "s3:GetObject"],
  "Resource": "arn:aws:s3:::example-bucket/*"
}

medium

A. Denies all access to example-bucket

B. Allows uploading and downloading objects only in example-bucket

C. Allows full access to all S3 buckets

D. Allows deleting objects in example-bucket

Solution

1. Step 1: Analyze actions in the policy

   The policy allows s3:PutObject (upload) and s3:GetObject (download) actions.

2. Step 2: Check resource scope

   The resource is limited to objects inside example-bucket, so permissions apply only there.

3. Final Answer:

   Allows uploading and downloading objects only in example-bucket -> Option B

4. Quick Check:

   Actions + resource = upload/download in example-bucket [OK]

Hint: Check actions and resource ARN carefully [OK]

Common Mistakes:

• Assuming delete permission is included
• Thinking permissions apply to all buckets
• Confusing allow with deny

4. You created an IAM policy to allow only starting EC2 instances but users report they can also stop instances. What is the likely mistake?

medium

A. The users have an additional policy granting stop permissions

B. The policy includes both ec2:StartInstances and ec2:StopInstances actions

C. The policy is attached to the wrong user

D. The policy uses wildcard * for all EC2 actions

Solution

1. Step 1: Understand the reported behavior

   Users can stop instances, which is not intended by the new policy.

2. Step 2: Identify possible causes

   If the policy only allows starting, but users can stop, they likely have another policy granting stop permissions.

3. Final Answer:

   Users have an additional policy granting stop permissions -> Option A

4. Quick Check:

   Multiple policies combine permissions [OK]

Hint: Check all policies attached to users [OK]

Common Mistakes:

• Assuming one policy overrides others
• Not checking group or role policies
• Ignoring policy wildcards

5. You want to apply the least privilege principle for a developer who needs to manage Lambda functions but only in the dev-environment. Which approach is best?

hard

A. Give the developer admin access to manage Lambda

B. Create an IAM policy allowing all Lambda actions on all functions

C. Attach the AWS managed policy AWSLambdaFullAccess to the developer

D. Create an IAM policy allowing only Lambda actions on functions with resource ARN containing dev-environment

Solution

1. Step 1: Identify the scope of access needed

   The developer needs to manage Lambda functions only in the dev-environment.

2. Step 2: Apply least privilege by limiting actions and resources

   Create an IAM policy allowing only Lambda actions on functions with resource ARN containing dev-environment restricts Lambda actions to only functions in dev-environment, minimizing risk.

3. Step 3: Evaluate other options

   Options B, C, and D grant broader access than needed, violating least privilege.

4. Final Answer:

   Create an IAM policy allowing only Lambda actions on functions with resource ARN containing dev-environment -> Option D

5. Quick Check:

   Least privilege = limit actions + resource scope [OK]

Hint: Limit permissions by resource tags or names [OK]

Common Mistakes:

• Using broad AWS managed policies
• Granting admin or full access unnecessarily
• Ignoring resource-level restrictions