Few AWS errors are more common than AccessDenied.

 

AWS S3 Error: AccessDenied 🚫

Few AWS errors are more common than:

An error occurred (AccessDenied) when calling the PutObject operation: Access Denied

The good news is that this error usually means AWS is protecting something.

The challenge is figuring out which protection mechanism is blocking you.

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📌 Key Term

AccessDenied

AWS received your request, understood it, and intentionally refused it.

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What AWS Is Telling You

When you see AccessDenied, AWS is saying:

"I know who you are, but you don't have permission to do this."

This is different from an authentication problem.

You successfully reached AWS.

AWS simply rejected the operation.

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The Three Most Common Causes

1. IAM Permissions

The user or role may not have permission to write to the bucket.

Check for permissions such as:

{
  "Effect": "Allow",
  "Action": "s3:PutObject",
  "Resource": "arn:aws:s3:::my-bucket/*"
}

Notice the trailing /*.

Without it, you may have access to the bucket itself but not the objects inside it.

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📌 Common Mistake

Granting access to:

arn:aws:s3:::my-bucket

but forgetting:

arn:aws:s3:::my-bucket/*

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2. Bucket Policies

Even if IAM permissions look correct, the bucket may contain a policy that blocks access.

Bucket policies can override what appears to be a valid IAM configuration.

Look for statements containing:

{
  "Effect": "Deny"
}

A single explicit deny can stop the request immediately.

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📌 Key Term

Explicit Deny

A deny rule that overrides all allow rules.

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3. Encryption Settings

Many organizations require uploads to use a specific KMS key.

If the upload is encrypted incorrectly, S3 may reject it.

Common examples include:

• Missing KMS permissions
• Wrong KMS key
• Missing encryption headers

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Quick Troubleshooting Commands

Verify who AWS thinks you are:

aws sts get-caller-identity

Check whether the bucket exists and is reachable:

aws s3api head-bucket --bucket my-bucket

Attempt a test upload:

aws s3 cp test.txt s3://my-bucket/

The resulting error often contains useful clues.

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📌 Remember

S3 permissions are often controlled by multiple layers:

IAM

Bucket Policy

KMS

Organizations SCPs

Check all of them before assuming the problem is IAM alone.

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The Fast Path

When troubleshooting AccessDenied, start with:

1. Confirm your identity with sts get-caller-identity
2. Verify s3:PutObject permissions
3. Check bucket policies for explicit denies
4. Review KMS encryption requirements
5. Check for organization-level restrictions

In many environments, the problem is not missing permissions.

It's a policy somewhere that is intentionally blocking the request.

Once you find that policy, the fix is usually straightforward.

Happy troubleshooting! ☁️