CVE-2026-44431: urllib3: Sensitive headers forwarded across origins in proxied low-level redirects

### Impact When following cross-origin redirects for requests made using urllib3’s high-level APIs, such as `urllib3.request()`, `PoolManager.request()`, and `ProxyManager.request()`, sensitive headers — `Authorization`, `Cookie`, and `Proxy-Authorization` (defined in `Retry.DEFAULT_REMOVE_HEADERS_ON_REDIRECT`) — are stripped by default, as expected. However, cross-origin redirects followed from the low-level API via `ProxyManager.connection_from_url().urlopen(..., assert_same_host=False)` still forward these sensitive headers. ### Affected usage Applications and libraries using urllib3 versions earlier than 2.7.0 may be affected if they allow cross-origin redirects while making requests through `HTTPConnection.urlopen()` instances created via `ProxyManager.connection_from_url()`. ### Remediation Upgrade to urllib3 version 2.7.0 or later, in which sensitive headers are stripped from redirects followed by `HTTPConnection`. If upgrading is not immediately possible, avoid using this low-level redirect flow for cross-origin redirects. If appropriate for your use case, switch to `ProxyManager.request()`.