Summary In koa < 2.16.1 and < 3.0.0-alpha.5, passing untrusted user input to ctx.redirect() even after sanitizing it, may execute javascript code on the user who use the app.
Patches This issue is patched in 2.16.1 and 3.0.0-alpha.5.
PoC Coming soon...
Impact 1. Redirect user to another phishing site 2. Make request to another endpoint of the application based on user's cookie 3. Steal user's cookie