Detect HTTPS interception (#1430)

* WIP: Implement HTTPS interception detection by Durumeric, et. al.

Special thanks to @FiloSottile for guidance with the custom listener.

* Add {{.IsMITM}} context action and {mitm} placeholder

* Improve MITM detection heuristics for Firefox and Edge

* Add tests for MITM detection heuristics

* Improve Safari heuristics for interception detection

* Read ClientHello during first Read() instead of during Accept()

As far as I can tell, reading the ClientHello during Accept() prevents
new connections from being accepted during the read. Since Read() should
be called in its own goroutine, this keeps Accept() non-blocking.

* Clean up MITM detection handler; make possible to close connection

* Use standard lib cipher suite values when possible

* Improve Edge heuristics and test cases

* Refactor MITM checking logic; add some debug statements for now

* Fix bug in MITM heuristic tests and actual heuristic code

* Fix gofmt

* Remove debug statements; preparing for merge

CONTRIBUTING.md

@@ -99,7 +99,9 @@ one collaborator who did not open the pull request before merging. This will
 help ensure high code quality as new collaborators are added to the project.
 
 Read [CodeReviewComments](https://github.com/golang/go/wiki/CodeReviewComments)
-on the Go wiki for an idea of what we look for in good, clean Go code.
+on the Go wiki for an idea of what we look for in good, clean Go code, and
+check out [what Linus suggests](https://gist.github.com/matthewhudson/1475276)
+for good commit messages.
 
 
 

caddy.go

@@ -5,6 +5,8 @@
 //   1. Set the AppName and AppVersion variables.
 //   2. Call LoadCaddyfile() to get the Caddyfile.
 //      Pass in the name of the server type (like "http").
+//      Make sure the server type's package is imported
+//      (import _ "github.com/mholt/caddy/caddyhttp").
 //   3. Call caddy.Start() to start Caddy. You get back
 //      an Instance, on which you can call Restart() to
 //      restart it or Stop() to stop it.

caddyhttp/httpserver/context.go

@@ -321,3 +321,14 @@ func (c Context) Files(name string) ([]string, error) {
 
 	return names, nil
 }
+
+// IsMITM returns true if it seems likely that the TLS connection
+// is being intercepted.
+func (c Context) IsMITM() bool {
+	if val, ok := c.Req.Context().Value(CtxKey("mitm")).(bool); ok {
+		return val
+	}
+	return false
+}
+
+type CtxKey string

caddyhttp/httpserver/replacer.go

@@ -298,6 +298,15 @@ func (r *replacer) getSubstitution(key string) string {
 			}
 		}
 		return requestReplacer.Replace(r.requestBody.String())
+	case "{mitm}":
+		if val, ok := r.request.Context().Value(CtxKey("mitm")).(bool); ok {
+			if val {
+				return "likely"
+			} else {
+				return "unlikely"
+			}
+		}
+		return "unknown"
 	case "{status}":
 		if r.responseRecorder == nil {
 			return r.emptyValue

caddyhttp/httpserver/server.go

@@ -47,6 +47,18 @@ func NewServer(addr string, group []*SiteConfig) (*Server, error) {
 	}
 
 	s.Server.Handler = s // this is weird, but whatever
+	tlsh := &tlsHandler{next: s.Server.Handler}
+	s.Server.ConnState = func(c net.Conn, cs http.ConnState) {
+		// when a connection closes or is hijacked, delete its entry
+		// in the map, because we are done with it.
+		if tlsh.listener != nil {
+			if cs == http.StateHijacked || cs == http.StateClosed {
+				tlsh.listener.helloInfosMu.Lock()
+				delete(tlsh.listener.helloInfos, c.RemoteAddr().String())
+				tlsh.listener.helloInfosMu.Unlock()
+			}
+		}
+	}
 
 	// Disable HTTP/2 if desired
 	if !HTTP2 {
@@ -75,6 +87,10 @@ func NewServer(addr string, group []*SiteConfig) (*Server, error) {
 		s.Server.TLSConfig.NextProtos = []string{"h2"}
 	}
 
+	if s.Server.TLSConfig != nil {
+		s.Server.Handler = tlsh
+	}
+
 	// Compile custom middleware for every site (enables virtual hosting)
 	for _, site := range group {
 		stack := Handler(staticfiles.FileServer{Root: http.Dir(site.Root), Hide: site.HiddenFiles})
@@ -156,7 +172,10 @@ func (s *Server) Serve(ln net.Listener) error {
 		// not implement the File() method we need for graceful restarts
 		// on POSIX systems.
 		// TODO: Is this ^ still relevant anymore? Maybe we can now that it's a net.Listener...
-		ln = tls.NewListener(ln, s.Server.TLSConfig)
+		ln = newTLSListener(ln, s.Server.TLSConfig, s.Server.ReadTimeout)
+		if handler, ok := s.Server.Handler.(*tlsHandler); ok {
+			handler.listener = ln.(*tlsHelloListener)
+		}
 
 		// Rotate TLS session ticket keys
 		s.tlsGovChan = caddytls.RotateSessionTicketKeys(s.Server.TLSConfig)