Enforcement of secure and specific Cross-Origin Resource Sharing (CORS) policies
import 'package:shelf/shelf.dart' as shelf;
void main() {
var handler = const shelf.Pipeline().addMiddleware(shelf.middleware.addHeaders({
// This is the vulnerable part of the code
'Access-Control-Allow-Origin': '*',
'Access-Control-Allow-Headers': 'Origin, X-Requested-With, Content-Type, Accept',
})).addHandler(_echoRequest);
shelf.serve(handler, 'localhost', 8080);
}
shelf.Response _echoRequest(shelf.Request request) {
return shelf.Response.ok('Request for "${request.url}"');
}
In the code above, the server is set to respond to every request with the headers
Access-Control-Allow-Origin
set to
*
and
Access-Control-Allow-Headers
set to
'Origin, X-Requested-With, Content-Type, Accept'
.
The
Access-Control-Allow-Origin
header determines which domains are allowed to access the resources on the server. By setting this to
*
, the server is allowing any domain to access its resources. This is a security vulnerability as it allows Cross-Origin Resource Sharing (CORS) from any origin, potentially exposing sensitive data to malicious sites.
The
Access-Control-Allow-Headers
header is used in response to a preflight request to indicate which HTTP headers can be used when making the actual request. This header is not directly a security vulnerability, but when combined with a wildcard
Access-Control-Allow-Origin
, it can contribute to potential security risks.
In conclusion, the vulnerability in the code lies in the indiscriminate use of the wildcard
*
in the
Access-Control-Allow-Origin
header, which opens up the server resources to be accessed from any origin.
import 'package:shelf/shelf.dart' as shelf;
void main() {
var handler = const shelf.Pipeline().addMiddleware(shelf.middleware.addHeaders({
// This is the fixed part of the code
'Access-Control-Allow-Origin': 'http://example.com', // replace with your specific domain
'Access-Control-Allow-Headers': 'Origin, X-Requested-With, Content-Type, Accept',
})).addHandler(_echoRequest);
shelf.serve(handler, 'localhost', 8080);
}
shelf.Response _echoRequest(shelf.Request request) {
return shelf.Response.ok('Request for "${request.url}"');
}
The original code had a vulnerability in the Cross-Origin Resource Sharing (CORS) configuration. The 'Access-Control-Allow-Origin' header was set to '*', which means that any domain can share resources with your application. This can lead to security issues as it allows any website to make a request to your server and read the response.
The fixed code replaces the wildcard '*' in the 'Access-Control-Allow-Origin' header with a specific domain ('http://example.com' in this case). This means that only this specific domain is allowed to share resources with your application.
If your application needs to share resources with multiple domains, you should implement a check in your server-side code to match the 'Origin' header of incoming requests against a list of allowed domains. If a match is found, set the 'Access-Control-Allow-Origin' header to the matched domain in the response.
Also, ensure that the 'Access-Control-Allow-Headers' only includes the specific headers that are necessary for your application. This can help to prevent potential security issues related to header injection.