CVE-2021-28363

The urllib3 library 1.26.x before 1.26.4 for Python omits SSL certificate validation in some cases involving HTTPS to HTTPS proxies. The initial connection to the HTTPS proxy (if an SSLContext isn't given via proxy_config) doesn't verify the hostname of the certificate. This means certificates for different servers that still validate properly with the default urllib3 SSLContext will be silently accepted.

The urllib3 library 1.26.x before 1.26.4 for Python omits SSL certificate validation in some cases involving HTTPS to HTTPS proxies. The initial connection to the HTTPS proxy (if an SSLContext isn't given via proxy_config) doesn't verify the hostname of the certificate. This means certificates for different servers that still validate properly with the default urllib3 SSLContext will be silently accepted.

The urllib3 library 1.26.x before 1.26.4 for Python omits SSL certificate validation in some cases involving HTTPS to HTTPS proxies. The initial connection to the HTTPS proxy (if an SSLContext isn't given via proxy_config) doesn't verify the hostname of the certificate. This means certificates for different servers that still validate properly with the default urllib3 SSLContext will be silently accepted.

### Impact Users who are using an HTTPS proxy to issue HTTPS requests and haven't configured their own SSLContext via `proxy_config`. Only the default SSLContext is impacted. ### Patches [urllib3 >=1.26.4 has the issue resolved](https://github.com/urllib3/urllib3/releases/tag/1.26.4). urllib3<1.26 is not impacted due to not supporting HTTPS requests via HTTPS proxies. ### Workarounds Upgrading is recommended as this is a minor release and not likely to break current usage. Configuring an `SSLContext` with `check_hostname=True` and passing via `proxy_config` instead of relying on the default `SSLContext` ### For more information If you have any questions or comments about this advisory: * Email us at [sethmichaellarson@gmail.com](mailto:sethmichaellarson@gmail.com)

La biblioteca urllib3 versiones 1.26.x anteriores a 1.26.4 para Python, omite una comprobación del certificado SSL en algunos casos que involucran HTTPS a proxies HTTPS.&#xa0;La conexión inicial al proxy HTTPS (si no se proporciona un SSLContext por medio de proxy_config) no verifica el nombre de host del certificado.&#xa0;Esto significa que los certificados para diferentes servidores que aún se comprueban apropiadamente con el urllib3 SSLContext predeterminado serán aceptados silenciosamente