How to troubleshoot authorization issues (for example, by using CloudTrail, IAM Access Advisor, and IAM policy simulator)

What is AWS CloudTrail, and how is it useful in troubleshooting authorization issues?

AWS CloudTrail is a service that provides a record of actions taken by a user, role, or an AWS service in an AWS account. It is useful for troubleshooting authorization issues because it allows you to audit and track each API call, including who made the call, from where it was made, and what actions were requested. This data can help determine the root cause of access denials or unexpected behavior in AWS environments.

How can IAM Access Advisor help in resolving permission issues?

IAM Access Advisor is a feature that helps administrators understand and refine their IAM policies by showing the service permissions granted to a user and when those services were last accessed. It is useful for resolving permission issues by identifying unused permissions that can be safely removed, thereby reducing the risk of unauthorized access and improving the principle of least privilege.

Describe a scenario where you would use the IAM policy simulator to troubleshoot authorization issues?

The IAM policy simulator is a tool used to troubleshoot and understand the effects of IAM policies by simulating whether a particular set of permissions will allow or deny access to AWS resources. A scenario for using this tool could involve simulating whether a newly updated IAM policy correctly grants the necessary permissions for a user to access specific resources without overly broad access, thereby preventing potential authorization issues.

Can you give an example of how to identify a denied request using AWS CloudTrail and correlate it to a specific IAM policy statement?

Yes, by using AWS CloudTrail logs, you can look for “EventName” entries such as “PutObject” or “GetItem” that have an “ErrorCode” of “AccessDenied.” Then, you can examine the “userIdentity” element to identify the user or role that made the request, and the “requestParameters” to see what resource was being accessed. Correlate this information with the IAM policy statements applied to the user or role to pinpoint the specific statement or absence of a necessary statement causing the denial.

What steps would you follow to troubleshoot an instance where a user is unable to assume a role they have previously been able to assume?

I would start by auditing the CloudTrail logs to identify any changes to the trust policy or permission policy associated with the role in question. Then, I’d check if the IAM policy applied to the user was altered in a way that affects the user’s capability to assume the role. If there were no changes, I would use the IAM policy simulator to ensure that the user still has the `sts:AssumeRole` permission for the specific role.

How would you investigate an access denied issue related to a cross-account role access through CloudTrail logs?

In investigating cross-account role access issues with CloudTrail logs, I’d review the logs for the `AssumeRole` action and check for “AccessDenied” error codes. Ensure that the trust policy for the role permits the external account to assume it and that the IAM policies in the external account grant necessary permissions to assume the role. Verify external account ID and any conditions like multi-factor authentication (MFA) requirements or IP restrictions that may impact the access.

How might you use the IAM Access Advisor to enhance your security posture?

IAM Access Advisor can improve security posture by providing visibility into service access patterns. It shows which services are actually being used and when they were last accessed, enabling the administrator to revoke unnecessary permissions and tighten IAM policies, adhering to the principle of least privilege and thereby minimizing the attack surface.

What role do resource-based policies play in troubleshooting authorization issues, and how would you verify if a resource-based policy is causing an access problem?

Resource-based policies control access to resources rather than at the user or role level. If there’s an authorization issue with accessing a particular AWS resource, it’s important to check not only IAM user policies but also the resource-based policies attached to the resource itself. You can verify if a resource-based policy is causing an access problem by using the IAM policy simulator to simulate access or by reviewing the policy statements directly to ensure they allow the necessary actions.

How can you identify if a user has the necessary permissions to perform a service-specific action, like launching an EC2 instance, using the IAM policy simulator?

To identify if a user has the necessary permissions to perform an action like launching an EC2 instance, you would use the IAM policy simulator to simulate the `ec2:RunInstances` action for that user. If the user has the necessary permissions, the simulation will indicate the action is allowed. If it’s denied, the policy simulator will provide the reason, at which point you can adjust the IAM policy accordingly.

What is the potential impact of overly permissive IAM policies and how can tools like CloudTrail and IAM Access Advisor help mitigate this risk?

Overly permissive IAM policies pose a significant security risk as they can lead to unauthorized access or privilege escalation. CloudTrail can help mitigate this risk by providing logs that show which actions were taken by users or roles, highlighting potentially dangerous activity. IAM Access Advisor shows which permissions are used and can help identify excess permissions that haven’t been used recently, so you can limit IAM policies to only what’s necessary.

If a user is suddenly receiving “403 Forbidden” errors when accessing an S3 bucket, how would you use AWS CloudTrail and the IAM policy simulator to resolve the issue?

I would begin by checking CloudTrail to look for “AccessDenied” events related to the S3 bucket. Identifying the timestamp and associated user or role from these events is crucial. After identifying who is getting denied, I would use the IAM policy simulator to simulate the user’s or role’s permission to access the S3 bucket. By reviewing the policy simulation results, I could pinpoint required permissions that may be missing or explicitly denied. This may involve checking not only the IAM policies but also S3 bucket policies and ACLs.