Protect against user injection for registration CLI page

CHANGELOG.md

@@ -15,6 +15,7 @@
 - Give a warning when running Headscale with reverse proxy improperly configured for WebSockets [#788](https://github.com/juanfont/headscale/pull/788)
 - Fix subnet routers with Primary Routes [#811](https://github.com/juanfont/headscale/pull/811)
 - Added support for JSON logs [#653](https://github.com/juanfont/headscale/issues/653)
+- Sanitise the node key passed to registration url [#823](https://github.com/juanfont/headscale/pull/823)
 - Add support for generating pre-auth keys with tags [#767](https://github.com/juanfont/headscale/pull/767)
 - Add support for evaluating `autoApprovers` ACL entries when a machine is registered [#763](https://github.com/juanfont/headscale/pull/763)
 - Add config flag to allow Headscale to start if OIDC provider is down [#829](https://github.com/juanfont/headscale/pull/829)

api.go

@@ -9,6 +9,7 @@ import (
 
 	"github.com/gorilla/mux"
 	"github.com/rs/zerolog/log"
+	"tailscale.com/types/key"
 )
 
 const (
@@ -93,7 +94,34 @@ func (h *Headscale) RegisterWebAPI(
 ) {
 	vars := mux.Vars(req)
 	nodeKeyStr, ok := vars["nkey"]
-	if !ok || nodeKeyStr == "" {
+
+	if !NodePublicKeyRegex.Match([]byte(nodeKeyStr)) {
+		log.Warn().Str("node_key", nodeKeyStr).Msg("Invalid node key passed to registration url")
+
+		writer.Header().Set("Content-Type", "text/plain; charset=utf-8")
+		writer.WriteHeader(http.StatusUnauthorized)
+		_, err := writer.Write([]byte("Unauthorized"))
+		if err != nil {
+			log.Error().
+				Caller().
+				Err(err).
+				Msg("Failed to write response")
+		}
+
+		return
+	}
+
+	// We need to make sure we dont open for XSS style injections, if the parameter that
+	// is passed as a key is not parsable/validated as a NodePublic key, then fail to render
+	// the template and log an error.
+	var nodeKey key.NodePublic
+	err := nodeKey.UnmarshalText(
+		[]byte(NodePublicKeyEnsurePrefix(nodeKeyStr)),
+	)
+
+	if !ok || nodeKeyStr == "" || err != nil {
+		log.Warn().Err(err).Msg("Failed to parse incoming nodekey")
+
 		writer.Header().Set("Content-Type", "text/plain; charset=utf-8")
 		writer.WriteHeader(http.StatusBadRequest)
 		_, err := writer.Write([]byte("Wrong params"))
@@ -130,7 +158,7 @@ func (h *Headscale) RegisterWebAPI(
 
 	writer.Header().Set("Content-Type", "text/html; charset=utf-8")
 	writer.WriteHeader(http.StatusOK)
-	_, err := writer.Write(content.Bytes())
+	_, err = writer.Write(content.Bytes())
 	if err != nil {
 		log.Error().
 			Caller().

utils.go

@@ -17,6 +17,7 @@ import (
 	"os"
 	"path/filepath"
 	"reflect"
+	"regexp"
 	"strconv"
 	"strings"
 
@@ -64,6 +65,8 @@ const (
 	ZstdCompression = "zstd"
 )
 
+var NodePublicKeyRegex = regexp.MustCompile("nodekey:[a-fA-F0-9]+")
+
 func MachinePublicKeyStripPrefix(machineKey key.MachinePublic) string {
 	return strings.TrimPrefix(machineKey.String(), machinePublicHexPrefix)
 }
@@ -325,7 +328,9 @@ func GenerateRandomStringDNSSafe(size int) (string, error) {
 		if err != nil {
 			return "", err
 		}
-		str = strings.ToLower(strings.ReplaceAll(strings.ReplaceAll(str, "_", ""), "-", ""))
+		str = strings.ToLower(
+			strings.ReplaceAll(strings.ReplaceAll(str, "_", ""), "-", ""),
+		)
 	}
 
 	return str[:size], nil