Drupal uses the third-party Guzzle library for handling HTTP requests and responses to external services. Guzzle has released two security advisories:

Failure to strip the Cookie header on change in host or HTTP downgrade
Fix failure to strip Authorization header on HTTP downgrade

These do not affect Drupal core, but may affect some contributed projects or custom code on Drupal sites.

We are issuing this security advisory outside our regular Drupal security release window schedule since Guzzle has already published information about the vulnerabilities, and vulnerabilities might exist in contributed modules or custom modules that use Guzzle for outgoing requests. Guzzle has rated these vulnerabilities as high-risk.

This advisory is not covered by Drupal Steward.