CORS. Presigned URL. S3 - amazon-s3

Question

I've generated a presigned S3 POST URL. Using the return parameters, I then pass it into my code, but I keep getting this error Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource..
Whereas on Postman, I'm able to submit the form-data with one attached file.
On PostMan, I manually entered the parameters
The same parameters are then entered into my code.

Answer 1

You must edit the CORS Configuration to be public , something like:
<?xml version="1.0" encoding="UTF-8"?>
<CORSConfiguration xmlns="http://s3.amazonaws.com/doc/2006-03-01/">
<CORSRule>
<AllowedOrigin>*</AllowedOrigin>
<AllowedMethod>POST</AllowedMethod>
<MaxAgeSeconds>3000</MaxAgeSeconds>
<AllowedHeader>*</AllowedHeader>
</CORSRule>
</CORSConfiguration>

Answer 2

Unable to comment so adding this here. Contains Harvey's answer, but in the form of a text to make it easy to copy.
[
{
"AllowedHeaders": [
"*"
],
"AllowedMethods": [
"GET",
"PUT",
"POST"
],
"AllowedOrigins": [
"*"
],
"ExposeHeaders": []
}
]

Answer 3

I encountered this issue as well. My CORs configuration on my bucket seemed correct yet my presigned URLs were hitting CORs problems. It turns out my AWS_REGION for my presigner was not set to the aws region of the bucket. After setting AWS_REGION to the correct region, it worked fine. I'm annoyed that the CORS issue was such a red herring to a simple problem and wasted several hours of my time.

Answer 4

On my case I fixed it by having allowedMethods, and origins in S3. The menu is under the Permissions tab
[
{
"AllowedHeaders": [
"*"
],
"AllowedMethods": [
"GET",
"PUT",
"POST"
],
"AllowedOrigins": [
"*"
],
"ExposeHeaders": []
}
]

Answer 5

In my case I specifically needed to allow the PUT method in the S3 Bucket's CORS Configuration to use the presigned URL, not the GET method as in the accepted answer:
<?xml version="1.0" encoding="UTF-8"?>
<CORSConfiguration xmlns="http://s3.amazonaws.com/doc/2006-03-01/">
<CORSRule>
<AllowedOrigin>*</AllowedOrigin>
<AllowedMethod>PUT</AllowedMethod>
<MaxAgeSeconds>3000</MaxAgeSeconds>
<AllowedHeader>*</AllowedHeader>
</CORSRule>
</CORSConfiguration>

Answer 6

My issue was that for some reason - getSignedUrl returned a url like so:
https://my-bucket.s3.us-west-2.amazonaws.com/bucket-folder/file.jpg
I've removed the region part - us-west-2 - and that fixed it 🤷🏼‍♂️
So instead it is now
https://my-bucket.s3.amazonaws.com/bucket-folder/file.jpg

Answer 7

My issue was I had a trailing slash (/) at the end of the domain in "AllowedOrigins". Once I removed the slash, requests worked.

Answer 8

I used boto3 to add the cors policy, and this is what worked for me. Used the logic by #Pranav Joglekar
cors_configuration = {
'CORSRules': [{
'AllowedHeaders': ['*'],
'AllowedMethods': ['GET', 'PUT', 'POST'],
'AllowedOrigins': ['*'],
'ExposeHeaders': [],
'MaxAgeSeconds': 3000
}]
}
s3_client = get_s3_client()
s3_client.put_bucket_cors(Bucket='my_bucket_name',
CORSConfiguration=cors_configuration)

Answer 9

For me,it was because my bucket name had a hyphen in it (e.g. my-bucket). The signed URL would replace the hyphen in the bucket name with an underscore and then sign it. So this meant two things:
CORS wouldn't work because the URL technically wasn't correct
I couldn't just change the underscore back to the hyphen because then the signature would be wrong when AWS validated the signed URL
I eventually had to rename my bucket to something without a hyphen (e.g. mybucket) and then it worked fine with the following configuration:
<?xml version="1.0" encoding="UTF-8"?>
<CORSConfiguration xmlns="http://s3.amazonaws.com/doc/2006-03-01/">
<CORSRule>
<AllowedOrigin>*</AllowedOrigin>
<AllowedMethod>GET</AllowedMethod>
<AllowedMethod>PUT</AllowedMethod>
<AllowedMethod>POST</AllowedMethod>
<AllowedMethod>DELETE</AllowedMethod>
<MaxAgeSeconds>3000</MaxAgeSeconds>
<AllowedHeader>*</AllowedHeader>
</CORSRule>
</CORSConfiguration>

Answer 10

We have to specify only the required HTTP method. we were using the POST method for Presigned URL so removed the "GET" and "PUT" methods from "AllowedMethods"
[
{
"AllowedHeaders": [
"*"
],
"AllowedMethods": [
"POST"
],
"AllowedOrigins": [
"*"
],
"ExposeHeaders": []
}
]

Answer 11

I was getting similar CORS errors even with things properly configured.
Thanks to this answer, I discovered my Lambda#Edge that presigns was using a region that wasn't the right one for this bucket. (which was on us-east-1 for some default stack reason).
So I had to be explicit about the region when generating the presignedPost
reference:
https://stackoverflow.com/a/13703595/11832970

Answer 12

Check the url encoding. I had a url encoded version of the pre-resigned URL and that failed until I decoded it.