Decrypting HTTPS tunnels constitutes a man-in-the-middle attack from the overall network security point of view. These features also illustrate why users should be careful with trusting HTTPS connections and why the weakest link in the chain of HTTPS protections is rather fragile. Squid decryption features described here and elsewhere are designed for deployment with user consent or, at the very least, in environments where decryption without consent is legal. Decrypting HTTPS tunnels without user consent or knowledge may violate ethical norms and may be illegal in your jurisdiction. WARNING: HTTPS was designed to give users an expectation of privacy and security.

TBD: Document what happens of Squid does intercept a CONNECT request, either because Squid was configured to intercept traffic destined to another proxy OR because a possibly malicious client sent a hand-crafted CONNECT request knowing that it is going to be intercepted. Thus, it should not be necessary to intercept a CONNECT request. This is why the Squid default ACLs start with deny CONNECT !SSL_Ports and why you must have a very good reason to place any type of allow rule above them.Ī browser sends CONNECT requests when it is configured to talk to a proxy. Quite literally anything that uses a two-way TCP connection can be passed through a CONNECT tunnel. It is important to notice that the protocols passed through CONNECT are not limited to the ones Squid normally handles. Other tunneled protocols may not even use HTTP messages and URLs (e.g., telnet). With HTTPS, the above parts are present in encapsulated HTTP requests that flow through the tunnel, but Squid does not have access to those encrypted messages.

The URL path (e.g., /index.html or /secure/images/), The URL scheme or protocol (e.g., ftp://, voip://, itunes://, or telnet://), For example, many common parts of the request URL do not exist in a CONNECT request: When a browser establishes a CONNECT tunnel through Squid, Access Controls are able to control CONNECT requests, but only limited information is available. For the gory details on tunneling and the CONNECT method, please see RFC 2817 and the expired Tunneling TCP based protocols through Web proxy servers draft. By default, the proxy establishes a TCP connection to the specified server, responds with an HTTP 200 (Connection Established) response, and then shovels packets back and forth between the client and the server, without understanding or interpreting the tunneled traffic. The CONNECT method is a way to tunnel any kind of connection through an HTTP proxy. Squid interaction with these traffic types is discussed below.

opens an TLS connection to a secure proxy.

Opens a tunnel through a proxy to the origin server using the CONNECT request method, or

opens an TLS connection directly to the origin server, or.

When a client comes across an URL, it can do one of three things:

Direct TLS connection to a reverse proxy.

Feature: HTTPS (HTTP Secure or HTTP over TLS).

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