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S3: fix Access-Control-Allow-Headers handling in S3 CORS #12841

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Merged
merged 1 commit into from
Jul 8, 2025
Merged

S3: fix Access-Control-Allow-Headers handling in S3 CORS #12841

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11 changes: 8 additions & 3 deletions localstack-core/localstack/services/s3/cors.py
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Original file line number Diff line number Diff line change
Expand Up @@ -205,7 +205,12 @@ def stop_options_chain():

if requested_headers := request.headers.get("Access-Control-Request-Headers"):
# if the rule matched, it means all Requested Headers are allowed
response.headers["Access-Control-Allow-Headers"] = requested_headers.lower()
requested_headers_formatted = [
header.strip().lower() for header in requested_headers.split(",")
]
response.headers["Access-Control-Allow-Headers"] = ", ".join(
requested_headers_formatted
)

if expose_headers := rule.get("ExposeHeaders"):
response.headers["Access-Control-Expose-Headers"] = ", ".join(expose_headers)
Expand Down Expand Up @@ -266,8 +271,8 @@ def _match_rule(rule: CORSRule, method: str, headers: Headers) -> Optional[CORSR

lower_case_allowed_headers = {header.lower() for header in allowed_headers}
if "*" not in allowed_headers and not all(
header in lower_case_allowed_headers
for header in request_headers.lower().split(", ")
header.strip() in lower_case_allowed_headers
for header in request_headers.lower().split(",")
):
return

Expand Down
12 changes: 12 additions & 0 deletions tests/aws/services/s3/test_s3_cors.py
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Original file line number Diff line number Diff line change
Expand Up @@ -551,6 +551,18 @@ def test_cors_match_headers(
match_headers("opt-get-allowed-diff-casing", opt_req)
assert opt_req.ok

# test with specific headers and no space after the comma
opt_req = requests.options(
key_url,
headers={
"Origin": origin,
"Access-Control-Request-Method": "GET",
"Access-Control-Request-Headers": "x-amz-expected-bucket-owner,x-amz-server-side-encryption",
},
)
match_headers("opt-get-allowed-no-space", opt_req)
assert opt_req.ok

# test GET with Access-Control-Request-Headers: should not happen in reality, AWS is considering it like an
# OPTIONS request
get_req = requests.get(
Expand Down
27 changes: 22 additions & 5 deletions tests/aws/services/s3/test_s3_cors.snapshot.json
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Original file line number Diff line number Diff line change
Expand Up @@ -340,7 +340,7 @@
}
},
"tests/aws/services/s3/test_s3_cors.py::TestS3Cors::test_cors_match_headers": {
"recorded-date": "02-01-2024, 16:08:41",
"recorded-date": "07-07-2025, 17:12:03",
"recorded-content": {
"opt-get": {
"Body": "",
Expand Down Expand Up @@ -474,6 +474,23 @@
},
"StatusCode": 200
},
"opt-get-allowed-no-space": {
"Body": "",
"Headers": {
"Access-Control-Allow-Credentials": "true",
"Access-Control-Allow-Headers": "x-amz-expected-bucket-owner, x-amz-server-side-encryption",
"Access-Control-Allow-Methods": "GET",
"Access-Control-Allow-Origin": "https://localhost:4200",
"Access-Control-Max-Age": "3000",
"Content-Length": "0",
"Vary": "Origin, Access-Control-Request-Headers, Access-Control-Request-Method",
"date": "date",
"server": "<server:1>",
"x-amz-id-2": "<x-amz-id-2:8>",
"x-amz-request-id": "<x-amz-request-id:8>"
},
"StatusCode": 200
},
"get-non-allowed-with-acl": {
"Body": "test-cors",
"Headers": {
Expand All @@ -484,8 +501,8 @@
"accept-ranges": "bytes",
"date": "date",
"server": "<server:1>",
"x-amz-id-2": "<x-amz-id-2:8>",
"x-amz-request-id": "<x-amz-request-id:8>",
"x-amz-id-2": "<x-amz-id-2:9>",
"x-amz-request-id": "<x-amz-request-id:9>",
"x-amz-server-side-encryption": "AES256"
},
"StatusCode": 200
Expand All @@ -505,8 +522,8 @@
"accept-ranges": "bytes",
"date": "date",
"server": "<server:1>",
"x-amz-id-2": "<x-amz-id-2:9>",
"x-amz-request-id": "<x-amz-request-id:9>",
"x-amz-id-2": "<x-amz-id-2:10>",
"x-amz-request-id": "<x-amz-request-id:10>",
"x-amz-server-side-encryption": "AES256"
},
"StatusCode": 200
Expand Down
8 changes: 7 additions & 1 deletion tests/aws/services/s3/test_s3_cors.validation.json
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Original file line number Diff line number Diff line change
Expand Up @@ -12,7 +12,13 @@
"last_validated_date": "2023-07-31T10:31:40+00:00"
},
"tests/aws/services/s3/test_s3_cors.py::TestS3Cors::test_cors_match_headers": {
"last_validated_date": "2024-01-02T16:08:41+00:00"
"last_validated_date": "2025-07-07T17:12:04+00:00",
"durations_in_seconds": {
"setup": 1.68,
"call": 4.08,
"teardown": 1.07,
"total": 6.83
}
},
"tests/aws/services/s3/test_s3_cors.py::TestS3Cors::test_cors_match_methods": {
"last_validated_date": "2025-03-17T20:18:58+00:00"
Expand Down
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