S3: Improve Cors AllowedOrigin behaviour (#6007)

moto/s3/exceptions.py

@@ -52,6 +52,13 @@ class InvalidArgumentError(S3ClientError):
         super().__init__("InvalidArgument", message, *args, **kwargs)
 
 
+class AccessForbidden(S3ClientError):
+    code = 403
+
+    def __init__(self, msg):
+        super().__init__("AccessForbidden", msg)
+
+
 class BucketError(S3ClientError):
     def __init__(self, *args, **kwargs):
         kwargs.setdefault("template", "bucket_error")

moto/s3/responses.py

@@ -50,6 +50,7 @@ from .exceptions import (
     PreconditionFailed,
     InvalidRange,
     LockNotEnabled,
+    AccessForbidden,
 )
 from .models import s3_backends
 from .models import get_canned_acl, FakeGrantee, FakeGrant, FakeAcl, FakeKey
@@ -59,6 +60,7 @@ from .utils import (
     parse_region_from_url,
     compute_checksum,
     ARCHIVE_STORAGE_CLASSES,
+    cors_matches_origin,
 )
 from xml.dom import minidom
 
@@ -298,7 +300,7 @@ class S3Response(BaseResponse):
         elif method == "POST":
             return self._bucket_response_post(request, bucket_name)
         elif method == "OPTIONS":
-            return self._response_options(bucket_name)
+            return self._response_options(request.headers, bucket_name)
         else:
             raise NotImplementedError(
                 f"Method {method} has not been implemented in the S3 backend yet"
@@ -343,7 +345,7 @@ class S3Response(BaseResponse):
             return 404, {}, ""
         return 200, {}, ""
 
-    def _set_cors_headers(self, bucket):
+    def _set_cors_headers(self, headers, bucket):
         """
         TODO: smarter way of matching the right CORS rule:
         See https://docs.aws.amazon.com/AmazonS3/latest/userguide/cors.html
@@ -367,9 +369,13 @@ class S3Response(BaseResponse):
                     cors_rule.allowed_methods
                 )
             if cors_rule.allowed_origins is not None:
-                self.response_headers["Access-Control-Allow-Origin"] = _to_string(
-                    cors_rule.allowed_origins
-                )
+                origin = headers.get("Origin")
+                if cors_matches_origin(origin, cors_rule.allowed_origins):
+                    self.response_headers["Access-Control-Allow-Origin"] = origin
+                else:
+                    raise AccessForbidden(
+                        "CORSResponse: This CORS request is not allowed. This is usually because the evalution of Origin, request method / Access-Control-Request-Method or Access-Control-Request-Headers are not whitelisted by the resource's CORS spec."
+                    )
             if cors_rule.allowed_headers is not None:
                 self.response_headers["Access-Control-Allow-Headers"] = _to_string(
                     cors_rule.allowed_headers
@@ -383,7 +389,7 @@ class S3Response(BaseResponse):
                     cors_rule.max_age_seconds
                 )
 
-    def _response_options(self, bucket_name):
+    def _response_options(self, headers, bucket_name):
         # Return 200 with the headers from the bucket CORS configuration
         self._authenticate_and_authorize_s3_action()
         try:
@@ -395,7 +401,7 @@ class S3Response(BaseResponse):
                 "",
             )  # AWS S3 seems to return 403 on OPTIONS and 404 on GET/HEAD
 
-        self._set_cors_headers(bucket)
+        self._set_cors_headers(headers, bucket)
 
         return 200, self.response_headers, ""
 
@@ -1241,7 +1247,7 @@ class S3Response(BaseResponse):
             return self._key_response_post(request, body, bucket_name, query, key_name)
         elif method == "OPTIONS":
             # OPTIONS response doesn't depend on the key_name: always return 200 with CORS headers
-            return self._response_options(bucket_name)
+            return self._response_options(request.headers, bucket_name)
         else:
             raise NotImplementedError(
                 f"Method {method} has not been implemented in the S3 backend yet"

moto/s3/utils.py

@@ -5,7 +5,7 @@ import re
 import hashlib
 from urllib.parse import urlparse, unquote, quote
 from requests.structures import CaseInsensitiveDict
-from typing import Union, Tuple
+from typing import List, Union, Tuple
 import sys
 from moto.settings import S3_IGNORE_SUBDOMAIN_BUCKETNAME
 
@@ -212,3 +212,14 @@ def _hash(fn, args) -> bytes:
     except TypeError:
         # The usedforsecurity-parameter is only available as of Python 3.9
         return fn(*args).hexdigest().encode("utf-8")
+
+
+def cors_matches_origin(origin_header: str, allowed_origins: List[str]) -> bool:
+    if "*" in allowed_origins:
+        return True
+    if origin_header in allowed_origins:
+        return True
+    for allowed in allowed_origins:
+        if re.match(allowed.replace(".", "\\.").replace("*", ".*"), origin_header):
+            return True
+    return False

tests/test_s3/test_s3_utils.py

@@ -7,6 +7,7 @@ from moto.s3.utils import (
     clean_key_name,
     undo_clean_key_name,
     compute_checksum,
+    cors_matches_origin,
 )
 from unittest.mock import patch
 
@@ -141,3 +142,19 @@ def test_checksum_crc32():
 
 def test_checksum_crc32c():
     compute_checksum(b"somedata", "CRC32C").should.equal(b"MTM5MzM0Mzk1Mg==")
+
+
+def test_cors_utils():
+    "Fancy string matching"
+    assert cors_matches_origin("a", ["a"])
+    assert cors_matches_origin("b", ["a", "b"])
+    assert not cors_matches_origin("c", [])
+    assert not cors_matches_origin("c", ["a", "b"])
+
+    assert cors_matches_origin("http://www.google.com", ["http://*.google.com"])
+    assert cors_matches_origin("http://www.google.com", ["http://www.*.com"])
+    assert cors_matches_origin("http://www.google.com", ["http://*"])
+    assert cors_matches_origin("http://www.google.com", ["*"])
+
+    assert not cors_matches_origin("http://www.google.com", ["http://www.*.org"])
+    assert not cors_matches_origin("http://www.google.com", ["https://*"])

tests/test_s3/test_server.py

@@ -1,11 +1,13 @@
 import io
 from urllib.parse import urlparse, parse_qs
 import sure  # noqa # pylint: disable=unused-import
+import requests
 import pytest
 import xmltodict
 
 from flask.testing import FlaskClient
 import moto.server as server
+from moto.moto_server.threaded_moto_server import ThreadedMotoServer
 from unittest.mock import patch
 
 """
@@ -223,7 +225,7 @@ def test_s3_server_post_cors_exposed_header():
     preflight_headers = {
         "Access-Control-Request-Method": "POST",
         "Access-Control-Request-Headers": "origin, x-requested-with",
-        "Origin": "https://localhost:9000",
+        "Origin": "https://example.org",
     }
     # Returns 403 on non existing bucket
     preflight_response = test_client.options(
@@ -257,3 +259,91 @@ def test_s3_server_post_cors_exposed_header():
         for header_name, header_value in expected_cors_headers.items():
             assert header_name in preflight_response.headers
             assert preflight_response.headers[header_name] == header_value
+
+
+def test_s3_server_post_cors_multiple_origins():
+    """Test that Moto only responds with the Origin that we that hosts the server"""
+    # github.com/getmoto/moto/issues/6003
+
+    cors_config_payload = """<CORSConfiguration xmlns="http://s3.amazonaws.com/doc/2006-03-01/">
+  <CORSRule>
+    <AllowedOrigin>https://example.org</AllowedOrigin>
+    <AllowedOrigin>https://localhost:6789</AllowedOrigin>
+    <AllowedMethod>POST</AllowedMethod>
+  </CORSRule>
+</CORSConfiguration>
+    """
+
+    thread = ThreadedMotoServer(port="6789", verbose=False)
+    thread.start()
+
+    # Create the bucket
+    requests.put("http://testcors.localhost:6789/")
+    requests.put("http://testcors.localhost:6789/?cors", data=cors_config_payload)
+
+    # Test only our requested origin is returned
+    preflight_response = requests.options(
+        "http://testcors.localhost:6789/test",
+        headers={
+            "Access-Control-Request-Method": "POST",
+            "Origin": "https://localhost:6789",
+        },
+    )
+    assert preflight_response.status_code == 200
+    assert (
+        preflight_response.headers["Access-Control-Allow-Origin"]
+        == "https://localhost:6789"
+    )
+    assert preflight_response.content == b""
+
+    # Verify a request with unknown origin fails
+    preflight_response = requests.options(
+        "http://testcors.localhost:6789/test",
+        headers={
+            "Access-Control-Request-Method": "POST",
+            "Origin": "https://unknown.host",
+        },
+    )
+    assert preflight_response.status_code == 403
+    assert b"<Code>AccessForbidden</Code>" in preflight_response.content
+
+    # Verify we can use a wildcard anywhere in the origin
+    cors_config_payload = """<CORSConfiguration xmlns="http://s3.amazonaws.com/doc/2006-03-01/"><CORSRule>
+            <AllowedOrigin>https://*.google.com</AllowedOrigin>
+            <AllowedMethod>POST</AllowedMethod>
+          </CORSRule></CORSConfiguration>"""
+    requests.put("http://testcors.localhost:6789/?cors", data=cors_config_payload)
+    for origin in ["https://sth.google.com", "https://a.google.com"]:
+        preflight_response = requests.options(
+            "http://testcors.localhost:6789/test",
+            headers={"Access-Control-Request-Method": "POST", "Origin": origin},
+        )
+        assert preflight_response.status_code == 200
+        assert preflight_response.headers["Access-Control-Allow-Origin"] == origin
+
+    # Non-matching requests throw an error though - it does not act as a full wildcard
+    preflight_response = requests.options(
+        "http://testcors.localhost:6789/test",
+        headers={
+            "Access-Control-Request-Method": "POST",
+            "Origin": "sth.microsoft.com",
+        },
+    )
+    assert preflight_response.status_code == 403
+    assert b"<Code>AccessForbidden</Code>" in preflight_response.content
+
+    # Verify we can use a wildcard as the origin
+    cors_config_payload = """<CORSConfiguration xmlns="http://s3.amazonaws.com/doc/2006-03-01/"><CORSRule>
+                <AllowedOrigin>*</AllowedOrigin>
+                <AllowedMethod>POST</AllowedMethod>
+              </CORSRule></CORSConfiguration>"""
+    requests.put("http://testcors.localhost:6789/?cors", data=cors_config_payload)
+    for origin in ["https://a.google.com", "http://b.microsoft.com", "any"]:
+        preflight_response = requests.options(
+            "http://testcors.localhost:6789/test",
+            headers={"Access-Control-Request-Method": "POST", "Origin": origin},
+        )
+        assert preflight_response.status_code == 200
+        assert preflight_response.headers["Access-Control-Allow-Origin"] == origin
+
+    thread.stop()