Add support to restrict localserver response handling to specific origins

ee/localserver/krypto-ec-middleware.go

@@ -7,6 +7,7 @@ import (
 	"crypto/ecdsa"
 	"encoding/base64"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"log/slog"
@@ -20,7 +21,6 @@ import (
 	"github.com/kolide/launcher/pkg/log/multislogger"
 	"github.com/kolide/launcher/pkg/traces"
 	"go.opentelemetry.io/otel/attribute"
-	"go.opentelemetry.io/otel/codes"
 )
 
 const (
@@ -35,6 +35,7 @@ type v2CmdRequestType struct {
 	Body            []byte
 	CallbackUrl     string
 	CallbackHeaders map[string][]string
+	AllowedOrigins  []string
 }
 
 func (cmdReq v2CmdRequestType) CallbackReq() (*http.Request, error) {
@@ -79,8 +80,9 @@ func newKryptoEcMiddleware(slogger *slog.Logger, localDbSigner, hardwareSigner c
 type callbackErrors string
 
 const (
-	timeOutOfRangeErr  callbackErrors = "time-out-of-range"
-	responseFailureErr callbackErrors = "response-failure"
+	timeOutOfRangeErr   callbackErrors = "time-out-of-range"
+	responseFailureErr  callbackErrors = "response-failure"
+	originDisallowedErr callbackErrors = "origin-disallowed"
 )
 
 type callbackDataStruct struct {
@@ -96,7 +98,7 @@ type callbackDataStruct struct {
 // Also, because the URL is the box, we cannot cleanly do this through middleware. It reqires a lot of passing data
 // around through context. Doing it here, as part of kryptoEcMiddleware, allows for a fairly succint defer.
 //
-// Note that this should be a goroutine.
+// Note that because this is a network call, it should be called in a goroutine.
 func (e *kryptoEcMiddleware) sendCallback(req *http.Request, data *callbackDataStruct) {
 	if req == nil {
 		return
@@ -216,12 +218,47 @@ func (e *kryptoEcMiddleware) Wrap(next http.Handler) http.Handler {
 			}()
 		}
 
+		// Check if the origin is in the allowed list. See https://github.com/kolide/k2/issues/9634
+		if len(cmdReq.AllowedOrigins) > 0 {
+			allowed := false
+			for _, ao := range cmdReq.AllowedOrigins {
+				if strings.EqualFold(ao, r.Header.Get("Origin")) {
+					allowed = true
+					break
+				}
+			}
+
+			if !allowed {
+				span.SetAttributes(attribute.String("origin", r.Header.Get("Origin")))
+				traces.SetError(span, fmt.Errorf("origin %s is not allowed", r.Header.Get("Origin")))
+				e.slogger.Log(r.Context(), slog.LevelError,
+					"origin is not allowed",
+					"allowlist", cmdReq.AllowedOrigins,
+					"origin", r.Header.Get("Origin"),
+				)
+
+				w.WriteHeader(http.StatusUnauthorized)
+				callbackData.Error = originDisallowedErr
+				return
+			}
+
+			e.slogger.Log(r.Context(), slog.LevelDebug,
+				"origin matches allowlist",
+				"origin", r.Header.Get("Origin"),
+			)
+		} else {
+			e.slogger.Log(r.Context(), slog.LevelDebug,
+				"origin is allowed by default, no allowlist",
+				"origin", r.Header.Get("Origin"),
+			)
+		}
+
 		// Check the timestamp, this prevents people from saving a challenge and then
 		// reusing it a bunch. However, it will fail if the clocks are too far out of sync.
 		timestampDelta := time.Now().Unix() - challengeBox.Timestamp()
 		if timestampDelta > timestampValidityRange || timestampDelta < -timestampValidityRange {
 			span.SetAttributes(attribute.Int64("timestamp_delta", timestampDelta))
-			span.SetStatus(codes.Error, "timestamp is out of range")
+			traces.SetError(span, errors.New("timestamp is out of range"))
 			e.slogger.Log(r.Context(), slog.LevelError,
 				"timestamp is out of range",
 				"delta", timestampDelta,
@@ -234,13 +271,16 @@ func (e *kryptoEcMiddleware) Wrap(next http.Handler) http.Handler {
 
 		newReq := &http.Request{
 			Method: http.MethodPost,
+			Header: make(http.Header),
 			URL: &url.URL{
 				Scheme: r.URL.Scheme,
 				Host:   r.Host,
 				Path:   cmdReq.Path,
 			},
 		}
 
+		newReq.Header.Set("Origin", r.Header.Get("Origin"))
+
 		// setting the newReq context to the current request context
 		// allows the trace to continue to the inner request,
 		// maintains the same lifetime as the original request,

ee/localserver/krypto-ec-middleware_test.go

@@ -209,6 +209,153 @@ func TestKryptoEcMiddleware(t *testing.T) {
 	}
 }
 
+func Test_AllowedOrigin(t *testing.T) {
+	t.Parallel()
+
+	counterpartyKey, err := echelper.GenerateEcdsaKey()
+	require.NoError(t, err)
+
+	challengeId := []byte(ulid.New())
+	challengeData := []byte(ulid.New())
+
+	var tests = []struct {
+		name           string
+		requestOrigin  string
+		allowedOrigins []string
+		logStr         string
+		expectedStatus int
+	}{
+		{
+			name:           "no allowed specified",
+			requestOrigin:  "https://auth.example.com",
+			expectedStatus: http.StatusOK,
+			logStr:         "origin is allowed by default",
+		},
+		{
+			name:           "no allowed specified missing origin",
+			expectedStatus: http.StatusOK,
+			logStr:         "origin is allowed by default",
+		},
+		{
+			name:           "allowed specified missing origin",
+			allowedOrigins: []string{"https://auth.example.com", "https://login.example.com"},
+			expectedStatus: http.StatusUnauthorized,
+			logStr:         "origin is not allowed",
+		},
+		{
+			name:           "allowed specified origin mismatch",
+			allowedOrigins: []string{"https://auth.example.com", "https://login.example.com"},
+			requestOrigin:  "https://not-it.example.com",
+			expectedStatus: http.StatusUnauthorized,
+			logStr:         "origin is not allowed",
+		},
+		{
+			name:           "scheme mismatch",
+			allowedOrigins: []string{"https://auth.example.com"},
+			requestOrigin:  "http://auth.example.com",
+			expectedStatus: http.StatusUnauthorized,
+			logStr:         "origin is not allowed",
+		},
+		{
+			name:           "allowed specified origin matches",
+			allowedOrigins: []string{"https://auth.example.com", "https://login.example.com"},
+			requestOrigin:  "https://auth.example.com",
+			expectedStatus: http.StatusOK,
+			logStr:         "origin matches allowlist",
+		},
+		{
+			name:           "allowed specified origin matches 2",
+			allowedOrigins: []string{"https://auth.example.com", "https://login.example.com"},
+			requestOrigin:  "https://login.example.com",
+			expectedStatus: http.StatusOK,
+			logStr:         "origin matches allowlist",
+		},
+		{
+			name:           "allowed specified origin matches casing",
+			allowedOrigins: []string{"https://auth.example.com", "https://login.example.com"},
+			requestOrigin:  "https://AuTh.ExAmPlE.cOm",
+			expectedStatus: http.StatusOK,
+			logStr:         "origin matches allowlist",
+		},
+	}
+
+	for _, tt := range tests {
+		tt := tt
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			cmdReqBody := []byte(randomStringWithSqlCharacters(t, 100000))
+
+			cmdReq := v2CmdRequestType{
+				Path:           "whatevs",
+				Body:           cmdReqBody,
+				AllowedOrigins: tt.allowedOrigins,
+			}
+
+			challengeBytes, privateEncryptionKey, err := challenge.Generate(counterpartyKey, challengeId, challengeData, mustMarshal(t, cmdReq))
+			require.NoError(t, err)
+			encodedChallenge := base64.StdEncoding.EncodeToString(challengeBytes)
+
+			responseData := []byte(ulid.New())
+
+			testHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				reqBodyRaw, err := io.ReadAll(r.Body)
+				require.NoError(t, err)
+				defer r.Body.Close()
+
+				require.Equal(t, cmdReqBody, reqBodyRaw)
+				w.Write(responseData)
+			})
+
+			var logBytes bytes.Buffer
+			slogger := multislogger.New(slog.NewTextHandler(&logBytes, &slog.HandlerOptions{
+				Level: slog.LevelDebug,
+			})).Logger
+
+			// set up middlewares
+			kryptoEcMiddleware := newKryptoEcMiddleware(slogger, ecdsaKey(t), nil, counterpartyKey.PublicKey)
+			require.NoError(t, err)
+
+			h := kryptoEcMiddleware.Wrap(testHandler)
+
+			req := makeGetRequest(t, encodedChallenge)
+			req.Header.Set("origin", tt.requestOrigin)
+
+			rr := httptest.NewRecorder()
+			h.ServeHTTP(rr, req)
+
+			// FIXME: add some log string tests
+			//spew.Dump(logBytes.String(), tt.logStr)
+
+			require.Equal(t, tt.expectedStatus, rr.Code)
+
+			if tt.logStr != "" {
+				assert.Contains(t, logBytes.String(), tt.logStr)
+			}
+
+			if tt.expectedStatus != http.StatusOK {
+				return
+			}
+
+			// try to open the response
+			returnedResponseBytes, err := base64.StdEncoding.DecodeString(rr.Body.String())
+			require.NoError(t, err)
+
+			responseUnmarshalled, err := challenge.UnmarshalResponse(returnedResponseBytes)
+			require.NoError(t, err)
+			require.Equal(t, challengeId, responseUnmarshalled.ChallengeId)
+
+			opened, err := responseUnmarshalled.Open(*privateEncryptionKey)
+			require.NoError(t, err)
+			require.Equal(t, challengeData, opened.ChallengeData)
+			require.Equal(t, responseData, opened.ResponseData)
+			require.WithinDuration(t, time.Now(), time.Unix(opened.Timestamp, 0), time.Second*5)
+
+		})
+	}
+
+}
+
 func ecdsaKey(t *testing.T) *ecdsa.PrivateKey {
 	key, err := echelper.GenerateEcdsaKey()
 	require.NoError(t, err)

ee/localserver/request-id.go

@@ -25,6 +25,7 @@ type (
 		Nonce     string
 		Timestamp time.Time
 		Status    status
+		Origin    string
 	}
 
 	status struct {
@@ -78,6 +79,7 @@ func (ls *localServer) requestIdHandlerFunc(w http.ResponseWriter, r *http.Reque
 	response := requestIdsResponse{
 		Nonce:     ulid.New(),
 		Timestamp: time.Now(),
+		Origin:    r.Header.Get("Origin"),
 		Status: status{
 			EnrollmentStatus: string(enrollmentStatus),
 		},

ee/localserver/server.go

@@ -353,8 +353,10 @@ func (ls *localServer) startListener() (net.Listener, error) {
 
 func (ls *localServer) preflightCorsHandler(next http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		// Think harder, maybe?
-		// https://stackoverflow.com/questions/12830095/setting-http-headers
+		// We don't believe we can meaningfully enforce a CORS style check here -- those are enforced by the browser.
+		// And we recognize there are some patterns that bypass the browsers CORS enforcement. However, we do implement
+		// origin enforcement as an allowlist inside kryptoEcMiddleware
+		// See https://github.com/kolide/k2/issues/9634
 		if origin := r.Header.Get("Origin"); origin != "" {
 			w.Header().Set("Access-Control-Allow-Origin", origin)
 		}