HTTPS proxy connection (p_use_ssl/proxy_use_ssl) does not verify the proxy's certificate

Comienza en lib/net/http.rb#connect, específicamente en la rama @proxy_use_ssl que crea el SSLSocket del proxy. Compara su configuración con la conexión TLS al destino y determina cómo deben configurarse por separado la verificación del certificado del proxy y la comprobación del nombre de host. Se considera terminado cuando el certificado del proxy se verifica de forma predeterminada antes de enviar Proxy-Authorization, y se cubren todos los ajustes de verificación necesarios.

When connecting to a destination over TLS through a TLS proxy (an "HTTPS proxy"), enabling p_use_ssl encrypts the client→proxy hop but does not authenticate the proxy's certificate. The proxy TLS socket is built with no SSLContext and no post-connection check, so it defaults to VERIFY_NONE. This makes the proxy hop MITM-able, which matters because the Proxy-Authorization (Basic) credential is written over that socket in the CONNECT request.

Setup

Either of the documented ways to enable a TLS proxy:

  proxy = Net::HTTP.Proxy('proxy.example.com', 8080, 'user', 'pass', true)  # 5th arg -> @proxy_use_ssl
  http  = proxy.new('login.example.com', 443)
  http.use_ssl = true
  # ...or Net::HTTP.new(addr, port, p_addr, p_port, p_user, p_pass, p_no_proxy, true)
  http.get('/')

What happens

In Net::HTTP#connect, when @proxy_use_ssl is set, the proxy socket is wrapped as:

  proxy_sock = OpenSSL::SSL::SSLSocket.new(s)   # no SSLContext passed
  ssl_socket_connect(proxy_sock, @open_timeout)
  # ... then CONNECT + "Proxy-Authorization: Basic <creds>" is written to proxy_sock

SSLSocket.new(s) with no context uses a default context (verify_mode effectively VERIFY_NONE), and there is no post_connection_check on proxy_sock— the only post_connection_check in connect targets @address (the destination). So:

• The destination cert is verified (via @ssl_context + post_connection_check(@address)). ✅
• The proxy cert is neither verified nor hostname-checked. ❌

A MITM on the client→proxy path can therefore present any certificate, terminate the TLS, and read the Proxy-Authorization credential — the same credential exposure that enabling proxy TLS is meant to prevent.

Expected

The proxy TLS connection should verify the proxy certificate by default (use an SSLContext with VERIFY_PEER and run post_connection_check against the proxy host), consistent with how the destination connection is verified. At minimum there should be a way to supply verification settings (CA store, verify_mode, hostname) for the proxy connection distinct from the destination's.

Environment

• Ruby 4.0.5
• net-http 0.9.1
• Reproduced by reading lib/net/http.rb#connect (the if @proxy_use_ssl branch) — the proxy SSLSocket is built without a context and gets no post_connection_check.

Related

• jnunemaker/httparty#839 tracks a separate, complementary gap: HTTParty can't even set p_use_ssl (it passes only 6 of Net::HTTP.new's proxy args). This net-http issue is about the flag existing but not verifying the proxy cert.