A flaw was found in libsoup. When establishing HTTPS tunnels through a configured HTTP proxy, sensitive session cookies are transmitted in cleartext within the initial HTTP CONNECT request. A network-positioned attacker or a malicious HTTP proxy can intercept these cookies, leading to potential session hijacking or user impersonation.
To mitigate this issue, ensure that all HTTP proxies used for HTTPS tunnels are trusted and operate within a secure network. Avoid configuring applications to use untrusted HTTP proxies. If feasible, configure applications to bypass proxies for sensitive connections or utilize a secure proxy solution that encrypts the entire communication channel. A service restart or application reload may be required for changes to take effect.