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Resolving AWS “Access Denied” Errors: A Simple Guide

Learn how to troubleshoot AWS “Access Denied” errors caused by insufficient permissions, misconfigured policies, or organizational restrictions. This guide covers identifying API call sources, verifying policies (identity-based, resource-based, SCPs, and session), and debugging error messages step-by-step. Ensure accurate permissions alignment to address common issues effectively. Use our free chatbot to help resolve technical challenges.

Key Takeaways

• AWS “Access Denied” errors occur due to inadequate permissions, misconfigured policies, or organizational restrictions.
• Verify user permissions, Service Control Policies (SCPs), resource-based policies, and session policies.
• Understand and leverage AWS policy evaluation logic for resolution.
• Debug the IAM error message to identify which specific permissions are missing or denied.

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Step-by-Step Guide: Resolving AWS “Access Denied” Errors

Step 1: Identify the Source of the API Call

To effectively resolve the issue, you need to determine whether the request is made by:

• An IAM user.
• An IAM role.
• An AWS service using a service-linked role.

Steps:

1. Log in to the AWS Management Console.
2. Open CloudTrail to monitor the API activity leading to the error.
3. Review the error message in the request response to identify the denied action and the principal making the call.

Expert Tip: If the request is coming from an EC2 instance, check the Instance IAM Role for necessary permissions.

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Step 2: Verify Identity-Based Policies

Identity-based IAM policies define the permissions a user or role has.

Steps:

1. Navigate to the IAM console → Policies.
2. Confirm whether the given user or role has permissions for the specific action. For example:
   • Actions for Amazon S3: s3:GetObject, s3:PutObject.
   • Actions for DynamoDB: dynamodb:PutItem, dynamodb:Query.

Example Policy:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "s3:GetObject",
        "s3:PutObject"
      ],
      "Resource": "arn:aws:s3:::example-bucket/*"
    }
  ]
}

3. Look for explicit Deny statements which override Allow actions.

Note: Use the IAM Policy Simulator to test and debug policies quickly.

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Step 3: Check Service Control Policies (SCPs)

If you’re using AWS Organizations, SCPs define permissions at the organizational level.

Steps:

1. Open the AWS Organizations console.
2. Verify the SCPs associated with the account. Confirm they allow the required action.
3. Update the SCP if necessary. An example SCP update:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": ["s3:*"],
      "Resource": "*"
    }
  ]
}

Common Issue: SCPs deny access to management services by default. Always review SCPs when troubleshooting Access Denied errors.

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Step 4: Evaluate Resource-Based Policies

Resource-based policies (e.g., for S3 buckets or DynamoDB tables) must also allow the action.

Steps:

1. Open the resource in question, like an S3 bucket or Lambda function.
2. Review its policy document through the console or AWS CLI:
   • For S3: Check the bucket policy via Amazon S3 console.
   • For Lambda: Check the policy in the function settings.
3. Ensure there’s an Allow statement for the principal making the request.

Example S3 Bucket Policy:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": "*",
      "Action": "s3:GetObject",
      "Resource": "arn:aws:s3:::example-bucket/*"
    }
  ]
}

Important: Over-permissive resource policies can lead to security vulnerabilities. Be specific when defining allowed principals and actions.

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Step 5: Check Permission Boundaries

Permission boundaries are advanced IAM controls that define maximum permissions for users or roles.

Steps:

1. Check if a permission boundary is set for the IAM user or role.
2. If an action is denied, update the boundary to include the required actions.

Permission Boundary Example:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [
        "ec2:StartInstances",
        "ec2:StopInstances"
      ],
      "Resource": "*"
    }
  ]
}

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Step 6: Debug Error Messages

Access denied errors often provide detailed context about the missing permissions.

Example Error Message:

User: arn:aws:iam::123456789012:user/JohnDoe is not authorized to perform: dynamodb:PutItem on resource: arn:aws:dynamodb:us-east-1:123456789012:table/MyTable

Steps to Debug:

1. Extract the missing action (e.g., dynamodb:PutItem).
2. Check the resource (e.g., arn:aws:dynamodb).
3. Update policies to allow the action on the resource.

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Recommended Tools

1. AWS Policy Simulator – Test custom IAM policies for troubleshooting.
2. Access Analyzer – Find overly permissive policies in your AWS environment.
3. CloudTrail – View API request logs to debug failed access attempts.

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Step 7: Leverage Session or Scoped Policies

If using AWS STS (Security Token Service) or temporary credentials, ensure session policies are not overly restrictive.

Troubleshooting:

• Session policies should align with identity-based and resource-based policies.
• Use tools like AWS CLI to test session permissions.

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Expert Advice: Avoiding “Access Denied” Errors

• Hierarchy of Policies: Remember, AWS evaluates permission hierarchically. Misalignment in any policy (SCP, identity-based, resource-based, session) will lead to denied access.
• Audit granted permissions regularly using IAM Access Advisor to review users’ last accessed services.
• Overlooked restraint? Permissions boundaries are often missed and cause confusion.

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Potential Affiliate Tools to Aid Debugging

• NordVPN: Establish secure connections when accessing AWS resources.
• EaseUS Backup Center: Securely back up IAM policy configurations before making changes.
• AdGuard Ad Blocker: Secure against unauthorized browser extensions that might tamper with your AWS session.

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FAQs: AWS Access Denied Errors

Q1: What is the primary cause of “Access Denied” errors in AWS?

A: Lack of required permissions in IAM policies or Service Control Policies (SCPs) is the primary cause.

Q2: How can I simulate permissions to debug errors?

A: Use the AWS Policy Simulator to test and troubleshoot IAM policies.

Q3: What happens if there’s a conflict between an Allow and a Deny statement in IAM?

A: An explicit Deny always overrides any Allow statement. AWS follows a default Deny first logic.

Q4: Can AWS Access Analyzer fix policies automatically?

A: No, AWS Access Analyzer identifies over-permissive policies but does not modify them. You must fix them manually.

Q5: How do cross-account access issues lead to access denied?

A: If roles in one account interact with resources in another, resource-based policies and trust relationships must explicitly authorize cross-account actions.

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