urllib3 before version 1.23 does not remove the Authorization HTTP header when following a cross-origin redirect . This can allow for credentials in the Authorization header to be exposed to unintended hosts or transmitted in cleartext. In the urllib3 library through 1.24.1 for Python, CRLF injection is possible if the attacker controls the request parameter. A credentials-exposure flaw was found in python-requests, where if a request with authentication is redirected from an HTTPS endpoint to an HTTP endpoint on the same host, the Authorization header is not stripped and the credentials can be read in plain text. A man-in-the-middle attacker could exploit this flaw to obtain a user#039;s valid credentials