Affected: psf requests

Requests is a HTTP library. Since Requests 2.3.0, Requests has been leaking Proxy-Authorization headers to destination servers when redirected to an HTTPS endpoint. This is a product of how we use `rebuild_proxies` to reattach the `Proxy-Authorization` header to requests. For HTTP connections sent through the tunnel, the proxy will identify the header in the request itself and remove it prior to forwarding to the destination server. However when sent over HTTPS, the `Proxy-Authorization` header must be sent in the CONNECT request as the proxy has no visibility into the tunneled request. This results in Requests forwarding proxy credentials to the destination server unintentionally, allowing a malicious actor to potentially exfiltrate sensitive information. This issue has been patched in version 2.31.0.

Affected: PyPI: requests

### Impact

Since Requests v2.3.0, Requests has been vulnerable to potentially leaking `Proxy-Authorization` headers to destination servers, specifically during redirects to an HTTPS origin. This is a product of how `rebuild_proxies` is used to recompute and [reattach the `Proxy-Authorization` header](https://github.com/psf/requests/blob/f2629e9e3c7ce3c3c8c025bcd8db551101cbc773/requests/sessions.py#L319-L328) to requests when redirected. Note this behavior has _only_ been observed to affect proxied requests when credentials are supplied in the URL user information component (e.g. `https://username:password@proxy:8080`).

**Current vulnerable behavior(s):**

1. HTTP → HTTPS: **leak** 2. HTTPS → HTTP: **no leak** 3. HTTPS → HTTPS: **leak** 4. HTTP → HTTP: **no leak**

For HTTP connections sent through the proxy, the proxy will identify the header in the request itself and remove it prior to forwarding to the destination server. However when sent over HTTPS, the `Proxy-Authorization` header must be sent in the CONNECT request as the proxy has no visibility into further tunneled requests. This results in Requests forwarding the header to the destination server unintentionally, allowing a malicious actor to potentially exfiltrate those credentials.

The reason this currently works for HTTPS connections in Requests is the `Proxy-Authorization` header is also handled by urllib3 with our usage of the ProxyManager in adapters.py with [`proxy_manager_for`](https://github.com/psf/reque…

Affected: PyPI: requests

Requests is a HTTP library. Since Requests 2.3.0, Requests has been leaking Proxy-Authorization headers to destination servers when redirected to an HTTPS endpoint. This is a product of how we use `rebuild_proxies` to reattach the `Proxy-Authorization` header to requests. For HTTP connections sent through the tunnel, the proxy will identify the header in the request itself and remove it prior to forwarding to the destination server. However when sent over HTTPS, the `Proxy-Authorization` header must be sent in the CONNECT request as the proxy has no visibility into the tunneled request. This results in Requests forwarding proxy credentials to the destination server unintentionally, allowing a malicious actor to potentially exfiltrate sensitive information. This issue has been patched in version 2.31.0.