Permissive Cross-Origin Resource Sharing (CORS) policy is security-sensitive. It has led in the past to the following vulnerabilities:
Same origin policy in browsers prevents, by default and for security-reasons, a javascript frontend to perform a cross-origin HTTP request to a resource that has a different origin (domain, protocol, or port) from its own. The requested target can append additional HTTP headers in response, called CORS, that act like directives for the browser and change the access control policy / relax the same origin policy.
Access-Control-Allow-Origin: untrustedwebsite.com. Access-Control-Allow-Origin: * origin header. You are at risk if you answered yes to any of those questions.
Access-Control-Allow-Origin header should be set only for a trusted origin and for specific resources. nodejs http built-in module:
const http = require('http');
const srv = http.createServer((req, res) => {
res.writeHead(200, { 'Access-Control-Allow-Origin': '*' }); // Sensitive
res.end('ok');
});
srv.listen(3000);
Express.js framework with cors middleware:
const app = express();
app.use((req, res, next) => {
res.header('Access-Control-Allow-Origin', '*'); // Sensitive
next();
});
nodejs http built-in module:
const http = require('http');
const srv = http.createServer((req, res) => {
res.writeHead(200, { 'Access-Control-Allow-Origin': 'trustedwebsite.com' }); // Compliant
res.end('ok');
});
srv.listen(3000);
Express.js framework with cors middleware:
const app = express();
app.use((req, res, next) => {
res.header('Access-Control-Allow-Origin', 'trustedwebsite.com'); // Compliant
next();
});