S3 AuthorizationHeaderMalformed: Correct the Request Signing Region

Problem

An S3 request fails with AuthorizationHeaderMalformed and an error detail saying the request used the wrong Region. This guide covers that specific diagnostic; malformed authorization can have other causes.

Check the Bucket Location

Using credentials allowed to inspect the bucket:

aws s3api get-bucket-location --bucket YOUR_BUCKET_NAME

For this API, a null location means us-east-1. The legacy EU value represents eu-west-1. Do not copy either value directly into a client Region setting.

Fix the Client Configuration

Set the SDK or CLI to the bucket's actual Region. A Python example:

import boto3
 
s3 = boto3.client("s3", region_name="eu-west-1")
response = s3.head_object(
    Bucket="YOUR_BUCKET_NAME",
    Key="existing-object.txt",
)
print(response["ResponseMetadata"]["HTTPStatusCode"])

Replace the Region, bucket, and key. Use the normal credential provider chain rather than embedding credentials in source code. Review explicit endpoint overrides and environment/profile settings if the application keeps selecting the wrong Region.

Verify

Retry the original operation with the corrected configuration. If the error changes to AccessDenied, investigate permissions separately; correcting signing does not grant access.

For manually signed requests, prefer a supported SDK and follow AWS Signature Version 4 requirements instead of editing an authorization header by hand.

Related Guide and Sources

• S3 403 permissions guide
• AWS S3 error definitions
• AWS GetBucketLocation