Package Instance

express vulnerable to XSS via response.redirect()
### Impact

In express <4.20.0, passing untrusted user input - even after sanitizing it - to `response.redirect()` may execute untrusted code

### Patches

this issue is patched in express 4.20.0

### Workarounds

users are encouraged to upgrade to the patched version of express, but otherwise can workaround this issue by making sure any untrusted inputs are safe, ideally by validating them against an explicit allowlist

### Details

successful exploitation of this vector requires the following:

1. The attacker MUST control the input to response.redirect()
1. express MUST NOT redirect before the template appears
1. the browser MUST NOT complete redirection before:
1. the user MUST click on the link in the template

Express.js Open Redirect in malformed URLs
### Impact

Versions of Express.js prior to 4.19.2 and pre-release alpha and beta versions before 5.0.0-beta.3 are affected by an open redirect vulnerability using malformed URLs.

When a user of Express performs a redirect using a user-provided URL Express performs an encode [using `encodeurl`](https://github.com/pillarjs/encodeurl) on the contents before passing it to the `location` header. This can cause malformed URLs to be evaluated in unexpected ways by common redirect allow list implementations in Express applications, leading to an Open Redirect via bypass of a properly implemented allow list.

The main method impacted is `res.location()` but this is also called from within `res.redirect()`.

### Patches

https://github.com/expressjs/express/commit/0867302ddbde0e9463d0564fea5861feb708c2dd
https://github.com/expressjs/express/commit/0b746953c4bd8e377123527db11f9cd866e39f94

An initial fix went out with `express@4.19.0`, we then patched a feature regression in `4.19.1` and added improved handling for the bypass in `4.19.2`.

### Workarounds

The fix for this involves pre-parsing the url string with either `require('node:url').parse` or `new URL`. These are steps you can take on your own before passing the user input string to `res.location` or `res.redirect`.

### Resources

https://github.com/expressjs/express/pull/5539
https://github.com/koajs/koa/issues/1800
https://expressjs.com/en/4x/api.html#res.location