koa-remove-trailing-slashes@2.0.1 vulnerabilities

koa-remove-trailing-slashes is a Koa middleware that makes sure all requests does not have trailing slashes

Affected versions of this package are vulnerable to Open Redirect via the use of trailing double slashes in the URL when accessing the vulnerable endpoint (such as https://example.com//attacker.example/). The vulnerable code is in index.js::removeTrailingSlashes(), as the web server uses relative URLs instead of absolute URLs.

PoC

// Run the code below to set up a vulnerable server instance
// Then access http://localhost:3000///example.com

const Koa = require('koa');
const removeTrailingSlashes = require('koa-remove-trailing-slashes');

const app = new Koa();

app.use(removeTrailingSlashes());

app.use(ctx => {
  ctx.body = 'Hello World';
});

app.listen(3000);

Upgrade koa-remove-trailing-slashes to version 2.0.2 or higher.