Learn about the interaction between IAM policies and resource policies in AWS S3 access control. Get insights on how conflicting policies affect user access to S3 buckets.
Table of Contents
Question
An IAM policy that allows access to an Amazon S3 bucket is attached to an IAM user. The Amazon S3 bucket has a bucket policy that denies the IAM user access to the bucket.
Which statement is true about the conflicting IAM and resource policies?
A. A resource policy always overrides an IAM policy. The IAM user cannot access the bucket.
B. An IAM policy always overrides a resource policy. The IAM user can access the bucket.
C. A policy with a deny statement overrides an allow statement. The IAM user cannot access the bucket.
D. A policy with an allow statement overrides an allow statement. The IAM user can access the bucket.
Answer
C. A policy with a deny statement overrides an allow statement. The IAM user cannot access the bucket.
Explanation
A policy with a deny statement overrides an allow statement. The IAM user cannot access the bucket.
In this example the resource policy overrides the IAM policy. However, that is not always the case. The restrictive policy always overrides the least restrictive policy.
In AWS Identity and Access Management (IAM), when both IAM policies and resource policies (such as S3 bucket policies) are applied to a resource like an S3 bucket, they are evaluated together. If there is a conflict between an allow and a deny statement, the deny statement takes precedence.
This means that even if the IAM policy allows access to the IAM user, if there is a deny statement in the bucket policy that denies access to the same user, the user will be denied access to the bucket. This is a critical aspect of AWS security and access control, ensuring that the most restrictive access controls take precedence to prevent unauthorized access to resources.
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