Error: 403 Forbidden — Why Your Amazon S3 Upload Works in One Region but Fails in Another

- October 08, 2025

Error: 403 Forbidden — Why Your Amazon S3 Upload Works in One Region but Fails in Another

How a simple region mix-up can trigger a 403 in S3

Problem

You’re pushing data to Amazon S3 using valid credentials — the same IAM user or role that’s worked flawlessly in another region. Suddenly, you hit:

Error: 403 Forbidden

You double-check your AWS keys, your bucket policy, even your VPC endpoints. Everything looks fine. So why does the exact same upload work in us-east-1 but fail in eu-west-1?

This 403 usually isn’t about authentication failure — it’s about region context. S3 is global, but your permissions and bucket endpoints are region-bound.

Clarifying the Issue

The 403 Forbidden response often appears when your SDK or CLI is targeting the wrong region, or when your bucket policy restricts access to a specific AWS region or principal.

Here’s what’s really going on:

S3 endpoints are region-specific. If you try to PUT or GET an object from the wrong endpoint, AWS sees it as a different resource.
IAM policies can contain region conditions. A policy like this will silently block access from elsewhere:

"Condition": { "StringEquals": { "aws:RequestedRegion": "us-east-1" } }

Replicated buckets aren’t write-symmetric. Cross-region replication copies objects from the source bucket, but not the other way around.
Temporary credentials (like STS tokens) can expire or become invalid in different regional sessions.

So even though your credentials are correct, your target context — region, endpoint, or policy scope — isn’t.

Why It Matters

This issue tends to surface when teams globalize workloads — adding edge locations, replicating data, or spinning up secondary regions for latency optimization.
If your automation or CI/CD pipeline assumes S3 is fully global, region misalignment will cause intermittent 403s that are hard to trace.

It also affects compliance-sensitive workloads where policies are bound to regional access control — like ensuring EU data stays in eu-west-1. A single region mismatch can trigger an outright block.

In short: S3 is global in name but regional in enforcement.

Key Terms

403 Forbidden: HTTP status indicating the request was valid, but the server refuses to authorize it.
Region Endpoint: The regional S3 service endpoint (e.g., s3.us-west-2.amazonaws.com).
aws:RequestedRegion: A policy context key that limits where actions may be performed.
Cross-Region Replication (CRR): Automatically copies objects between buckets in different AWS regions.
STS Token: Short-term credentials that may be region-specific when issued. Using an STS token generated in one region for actions in another can cause 403 errors even if the IAM permissions are valid.

Steps at a Glance

Verify your S3 bucket’s region.
Confirm your SDK or CLI target region matches the bucket.
Check for region restrictions in IAM or bucket policies.
Inspect your S3 endpoint configuration.
Test uploads with explicit regional endpoints.

Detailed Steps

Step 1 — Verify the bucket’s region
Use the CLI to check your bucket’s actual region:

aws s3api get-bucket-location --bucket my-bucket

Note the LocationConstraint — you must target that same region.

Step 2 — Confirm your AWS CLI or SDK configuration
Ensure your client is initialized for the right region:

aws configure get region

Or explicitly set it in your code:

s3 = boto3.client('s3', region_name='eu-west-1')

Step 3 — Check for region-bound IAM policies
Look for aws:RequestedRegion in your IAM or bucket policy conditions. Example:

{
  "Effect": "Deny",
  "Action": "s3:*",
  "Resource": "*",
  "Condition": { "StringNotEquals": { "aws:RequestedRegion": "us-east-1" } }
}

That will deny uploads from any region other than us-east-1.

Step 4 — Use regional endpoints explicitly
When using the AWS CLI or SDK, specify the bucket’s regional endpoint:

aws s3 cp file.txt s3://my-bucket/ --endpoint-url https://s3.eu-west-1.amazonaws.com

Step 5 — Avoid assumptions in cross-region scripts
In Terraform or Python automation, always inject region variables:

provider "aws" {
  region = var.region
}

Then, implement the same logic in Python to keep your application layer consistent with Terraform’s region configuration.

import boto3
s3 = boto3.client('s3', region_name='us-east-1')

Pro Tip: Bind Buckets and Clients Intentionally

When working across multiple regions, define explicit bucket-region pairs in your code or configuration. For example:

buckets = {
  'us-east-1': 'my-logs-us-east-1',
  'eu-west-1': 'my-logs-eu-west-1'
}

for region, bucket in buckets.items():
  s3 = boto3.client('s3', region_name=region)
  s3.put_object(Bucket=bucket, Key='heartbeat.txt', Body=b'OK')

This ensures your writes always land in-region and stay policy-compliant. It also improves scalability and compliance by guaranteeing data sovereignty — critical in multi-region, multi-account environments.

Bottom line: Region alignment is not optional in S3 — it’s structural.

Conclusion

A 403 Forbidden from S3 is often a sign of misalignment, not misconfiguration.
The credentials are fine — it’s your region, endpoint, or policy scope that’s off.

By being explicit about regions in every layer — SDKs, IAM policies, and IaC templates — you’ll eliminate one of the most persistent and confusing S3 failure modes.

In S3, clarity of region equals clarity of access.

Aaron Rose is a software engineer and technology writer at tech-reader.blog and the author of Think Like a Genius.

Search This Blog

Tech-Reader.blog