[BUGFIX] Set SNI on each redirect to avoid handshake failures / incor…

…rect server name (#306)

* Set SNI explicitly, in case it's a redirect (fix for #300)

* Fix the SNI issue correctly, using the host portion of addr, while respecting --server-name and --no-sni

* Clean up double error logging pointed out by dadrien

* Comply with RFC4366, do not set SNI server name for IP address

Co-authored-by: Adam Greene <copyright@mzpqnxow.com>
#306

modules/http/scanner.go

@@ -132,7 +132,7 @@ func (flags *Flags) Help() string {
 }
 
 // Protocol returns the protocol identifer for the scanner.
-func (s *Scanner) Protocol() string {
+func (scanner *Scanner) Protocol() string {
 	return "http"
 }
 
@@ -143,13 +143,13 @@ func (scanner *Scanner) Init(flags zgrab2.ScanFlags) error {
 
 	if fl.ComputeDecodedBodyHashAlgorithm == "sha1" {
 		scanner.decodedHashFn = func(body []byte) string {
-			raw_hash := sha1.Sum(body)
-			return fmt.Sprintf("sha1:%s", hex.EncodeToString(raw_hash[:]))
+			rawHash := sha1.Sum(body)
+			return fmt.Sprintf("sha1:%s", hex.EncodeToString(rawHash[:]))
 		}
 	} else if fl.ComputeDecodedBodyHashAlgorithm == "sha256" {
 		scanner.decodedHashFn = func(body []byte) string {
-			raw_hash := sha256.Sum256(body)
-			return fmt.Sprintf("sha256:%s", hex.EncodeToString(raw_hash[:]))
+			rawHash := sha256.Sum256(body)
+			return fmt.Sprintf("sha256:%s", hex.EncodeToString(rawHash[:]))
 		}
 	} else if fl.ComputeDecodedBodyHashAlgorithm != "" {
 		log.Panicf("Invalid ComputeDecodedBodyHashAlgorithm choice made it through zflags: %s", scanner.config.ComputeDecodedBodyHashAlgorithm)
@@ -239,18 +239,35 @@ func (scan *scan) dialContext(ctx context.Context, network string, addr string)
 
 // getTLSDialer returns a Dial function that connects using the
 // zgrab2.GetTLSConnection()
-func (scan *scan) getTLSDialer(t *zgrab2.ScanTarget) func(net, addr string) (net.Conn, error) {
-	return func(net, addr string) (net.Conn, error) {
-		outer, err := scan.dialContext(context.Background(), net, addr)
+func (scan *scan) getTLSDialer(t *zgrab2.ScanTarget) func(network, addr string) (net.Conn, error) {
+	return func(network, addr string) (net.Conn, error) {
+		outer, err := scan.dialContext(context.Background(), network, addr)
 		if err != nil {
 			return nil, err
 		}
-
 		cfg, err := scan.scanner.config.TLSFlags.GetTLSConfigForTarget(t)
 		if err != nil {
 			return nil, err
 		}
 
+		// Set SNI server name on redirects unless --server-name was used (issue #300)
+		//  - t.Domain is always set to the *original* Host so it's not useful for setting SNI
+		//  - host is the current target of the request in this context; this is true for the
+		//    initial request as well as subsequent requests caused by redirects
+		//  - scan.scanner.config.ServerName is the value from --server-name if one was specified
+
+		// If SNI is enabled and --server-name is not set, use the target host for the SNI server name
+		if !scan.scanner.config.NoSNI && scan.scanner.config.ServerName == "" {
+			host, _, err := net.SplitHostPort(addr)
+			if err != nil {
+				log.Errorf("getTLSDialer(): Something went wrong splitting host/port '%s': %s", addr, err)
+			}
+			// RFC4366: Literal IPv4 and IPv6 addresses are not permitted in "HostName"
+			if i := net.ParseIP(host); i == nil {
+				cfg.ServerName = host
+			}
+		}
+
 		if scan.scanner.config.OverrideSH {
 			cfg.SignatureAndHashes = []tls.SigAndHash{
 				{0x01, 0x04}, // rsa, sha256
@@ -262,7 +279,6 @@ func (scan *scan) getTLSDialer(t *zgrab2.ScanTarget) func(net, addr string) (net
 				{0x01, 0x06}, // rsa, sha512
 			}
 		}
-
 		tlsConn := scan.scanner.config.TLSFlags.GetWrappedConnection(outer, cfg)
 
 		// lib/http/transport.go fills in the TLSLog in the http.Request instance(s)
@@ -431,7 +447,7 @@ func (scan *scan) Grab() *zgrab2.ScanError {
 	bodyText := ""
 	decodedSuccessfully := false
 	decoder := encoder.NewDecoder()
-	
+
 	//"windows-1252" is the default value and will likely not decode correctly
 	if certain || encoding != "windows-1252" {
 		decoded, decErr := decoder.Bytes(buf.Bytes())