[FEATURE] Delay 1FA Authentication (#993)

* adaptively delay 1FA by the actual execution time of authentication
* should grow and shrink over time as successful attempts are made
* uses the average of the last 10 successful attempts to calculate
* starts at an average of 1000ms
* minimum is 250ms
* a random delay is added to the largest of avg or minimum
* the random delay is between 0ms and 85ms
* bump LDAP suite to 80s timeout
* bump regulation scenario to 45s
* add mutex locking
* amend logging
* add docs
* add tests

Co-authored-by: Clément Michaud <clement.michaud34@gmail.com>

docs/security/measures.md

@@ -28,6 +28,19 @@ that the attacker must also require the certificate to retrieve the cookies.
 Note that using [HSTS] has consequences. That's why you should read the blog
 post nginx has written on [HSTS].
 
+## Protection against username enumeration
+
+Authelia adaptively delays authentication attempts based on the mean (average) of the 
+previous 10 successful attempts, and a small random interval to make it even harder to 
+determine if the attempt was successful. On start it is assumed that the last 10 attempts 
+took 1000ms, this quickly grows or shrinks to the correct value over time regardless of the
+authentication backend. 
+
+The cost of this is low since in the instance of a user not existing it just sleeps to delay 
+the login. Lastly the absolute minimum time authentication can take is 250ms. Both of these measures
+also have the added effect of creating an additional delay for all authentication attempts reducing
+the likelihood a password can be brute-forced even if regulation settings are too permissive.
+ 
 ## Protections against password cracking (File authentication provider)
 
 Authelia implements a variety of measures to prevent an attacker cracking passwords if they

internal/handlers/const.go

@@ -39,3 +39,7 @@ const testInactivity = "10"
 const testRedirectionURL = "http://redirection.local"
 const testResultAllow = "allow"
 const testUsername = "john"
+
+const movingAverageWindow = 10
+const msMinimumDelay1FA = float64(250)
+const msMaximumRandomDelay = int64(85)

internal/handlers/handler_firstfactor.go

@@ -2,6 +2,9 @@ package handlers
 
 import (
 	"fmt"
+	"math"
+	"math/rand"
+	"sync"
 	"time"
 
 	"github.com/authelia/authelia/internal/authentication"
@@ -10,9 +13,63 @@ import (
 	"github.com/authelia/authelia/internal/session"
 )
 
+func movingAverageIteration(value time.Duration, successful bool, movingAverageCursor *int, execDurationMovingAverage *[]time.Duration, mutex sync.Locker) float64 {
+	mutex.Lock()
+	if successful {
+		(*execDurationMovingAverage)[*movingAverageCursor] = value
+		*movingAverageCursor = (*movingAverageCursor + 1) % movingAverageWindow
+	}
+
+	var sum int64
+
+	for _, v := range *execDurationMovingAverage {
+		sum += v.Milliseconds()
+	}
+	mutex.Unlock()
+
+	return float64(sum / movingAverageWindow)
+}
+
+func calculateActualDelay(ctx *middlewares.AutheliaCtx, execDuration time.Duration, avgExecDurationMs float64, successful *bool) float64 {
+	randomDelayMs := float64(rand.Int63n(msMaximumRandomDelay))
+	totalDelayMs := math.Max(avgExecDurationMs, msMinimumDelay1FA) + randomDelayMs
+	actualDelayMs := math.Max(totalDelayMs-float64(execDuration.Milliseconds()), 1.0)
+	ctx.Logger.Tracef("attempt successful: %t, exec duration: %d, avg execution duration: %d, random delay ms: %d, total delay ms: %d, actual delay ms: %d", *successful, execDuration.Milliseconds(), int64(avgExecDurationMs), int64(randomDelayMs), int64(totalDelayMs), int64(actualDelayMs))
+
+	return actualDelayMs
+}
+
+func delayToPreventTimingAttacks(ctx *middlewares.AutheliaCtx, requestTime time.Time, successful *bool, movingAverageCursor *int, execDurationMovingAverage *[]time.Duration, mutex sync.Locker) {
+	execDuration := time.Since(requestTime)
+	avgExecDurationMs := movingAverageIteration(execDuration, *successful, movingAverageCursor, execDurationMovingAverage, mutex)
+	actualDelayMs := calculateActualDelay(ctx, execDuration, avgExecDurationMs, successful)
+	time.Sleep(time.Duration(actualDelayMs) * time.Millisecond)
+}
+
 // FirstFactorPost is the handler performing the first factory.
 //nolint:gocyclo // TODO: Consider refactoring time permitting.
-func FirstFactorPost(ctx *middlewares.AutheliaCtx) {
+func FirstFactorPost(msInitialDelay time.Duration, delayEnabled bool) middlewares.RequestHandler {
+	var execDurationMovingAverage = make([]time.Duration, movingAverageWindow)
+
+	var movingAverageCursor = 0
+
+	var mutex = &sync.Mutex{}
+
+	for i := range execDurationMovingAverage {
+		execDurationMovingAverage[i] = msInitialDelay * time.Millisecond
+	}
+
+	rand.Seed(time.Now().UnixNano())
+
+	return func(ctx *middlewares.AutheliaCtx) {
+		var successful bool
+
+		requestTime := time.Now()
+
+		if delayEnabled {
+			defer delayToPreventTimingAttacks(ctx, requestTime, &successful, &movingAverageCursor, &execDurationMovingAverage, mutex)
+		}
+
 		bodyJSON := firstFactorRequestBody{}
 		err := ctx.ParseBody(&bodyJSON)
 
@@ -124,5 +181,8 @@ func FirstFactorPost(ctx *middlewares.AutheliaCtx) {
 			return
 		}
 
+		successful = true
+
 		Handle1FAResponse(ctx, bodyJSON.TargetURL, userSession.Username, userSession.Groups)
 	}
+}

internal/handlers/handler_firstfactor_test.go

@@ -2,7 +2,9 @@ package handlers
 
 import (
 	"fmt"
+	"sync"
 	"testing"
+	"time"
 
 	"github.com/golang/mock/gomock"
 	"github.com/stretchr/testify/assert"
@@ -30,7 +32,7 @@ func (s *FirstFactorSuite) TearDownTest() {
 }
 
 func (s *FirstFactorSuite) TestShouldFailIfBodyIsNil() {
-	FirstFactorPost(s.mock.Ctx)
+	FirstFactorPost(0, false)(s.mock.Ctx)
 
 	// No body
 	assert.Equal(s.T(), "Unable to parse body: unexpected end of JSON input", s.mock.Hook.LastEntry().Message)
@@ -42,7 +44,7 @@ func (s *FirstFactorSuite) TestShouldFailIfBodyIsInBadFormat() {
 	s.mock.Ctx.Request.SetBodyString(`{
 		"username": "test"
 	}`)
-	FirstFactorPost(s.mock.Ctx)
+	FirstFactorPost(0, false)(s.mock.Ctx)
 
 	assert.Equal(s.T(), "Unable to validate body: password: non zero value required", s.mock.Hook.LastEntry().Message)
 	s.mock.Assert401KO(s.T(), "Authentication failed. Check your credentials.")
@@ -67,7 +69,7 @@ func (s *FirstFactorSuite) TestShouldFailIfUserProviderCheckPasswordFail() {
 		"password": "hello",
 		"keepMeLoggedIn": true
 	}`)
-	FirstFactorPost(s.mock.Ctx)
+	FirstFactorPost(0, false)(s.mock.Ctx)
 
 	assert.Equal(s.T(), "Error while checking password for user test: Failed", s.mock.Hook.LastEntry().Message)
 	s.mock.Assert401KO(s.T(), "Authentication failed. Check your credentials.")
@@ -93,7 +95,7 @@ func (s *FirstFactorSuite) TestShouldCheckAuthenticationIsMarkedWhenInvalidCrede
 		"keepMeLoggedIn": true
 	}`)
 
-	FirstFactorPost(s.mock.Ctx)
+	FirstFactorPost(0, false)(s.mock.Ctx)
 }
 
 func (s *FirstFactorSuite) TestShouldFailIfUserProviderGetDetailsFail() {
@@ -117,7 +119,7 @@ func (s *FirstFactorSuite) TestShouldFailIfUserProviderGetDetailsFail() {
 		"password": "hello",
 		"keepMeLoggedIn": true
 	}`)
-	FirstFactorPost(s.mock.Ctx)
+	FirstFactorPost(0, false)(s.mock.Ctx)
 
 	assert.Equal(s.T(), "Error while retrieving details from user test: Failed", s.mock.Hook.LastEntry().Message)
 	s.mock.Assert401KO(s.T(), "Authentication failed. Check your credentials.")
@@ -139,7 +141,7 @@ func (s *FirstFactorSuite) TestShouldFailIfAuthenticationMarkFail() {
 		"password": "hello",
 		"keepMeLoggedIn": true
 	}`)
-	FirstFactorPost(s.mock.Ctx)
+	FirstFactorPost(0, false)(s.mock.Ctx)
 
 	assert.Equal(s.T(), "Unable to mark authentication: failed", s.mock.Hook.LastEntry().Message)
 	s.mock.Assert401KO(s.T(), "Authentication failed. Check your credentials.")
@@ -170,7 +172,7 @@ func (s *FirstFactorSuite) TestShouldAuthenticateUserWithRememberMeChecked() {
 		"password": "hello",
 		"keepMeLoggedIn": true
 	}`)
-	FirstFactorPost(s.mock.Ctx)
+	FirstFactorPost(0, false)(s.mock.Ctx)
 
 	// Respond with 200.
 	assert.Equal(s.T(), 200, s.mock.Ctx.Response.StatusCode())
@@ -210,7 +212,7 @@ func (s *FirstFactorSuite) TestShouldAuthenticateUserWithRememberMeUnchecked() {
 		"password": "hello",
 		"keepMeLoggedIn": false
 	}`)
-	FirstFactorPost(s.mock.Ctx)
+	FirstFactorPost(0, false)(s.mock.Ctx)
 
 	// Respond with 200.
 	assert.Equal(s.T(), 200, s.mock.Ctx.Response.StatusCode())
@@ -253,7 +255,7 @@ func (s *FirstFactorSuite) TestShouldSaveUsernameFromAuthenticationBackendInSess
 		"password": "hello",
 		"keepMeLoggedIn": true
 	}`)
-	FirstFactorPost(s.mock.Ctx)
+	FirstFactorPost(0, false)(s.mock.Ctx)
 
 	// Respond with 200.
 	assert.Equal(s.T(), 200, s.mock.Ctx.Response.StatusCode())
@@ -323,7 +325,7 @@ func (s *FirstFactorRedirectionSuite) TestShouldRedirectToDefaultURLWhenNoTarget
 		"password": "hello",
 		"keepMeLoggedIn": false
 	}`)
-	FirstFactorPost(s.mock.Ctx)
+	FirstFactorPost(0, false)(s.mock.Ctx)
 
 	// Respond with 200.
 	s.mock.Assert200OK(s.T(), redirectResponse{Redirect: "https://default.local"})
@@ -343,7 +345,7 @@ func (s *FirstFactorRedirectionSuite) TestShouldRedirectToDefaultURLWhenURLIsUns
 		"targetURL": "http://notsafe.local"
 	}`)
 
-	FirstFactorPost(s.mock.Ctx)
+	FirstFactorPost(0, false)(s.mock.Ctx)
 
 	// Respond with 200.
 	s.mock.Assert200OK(s.T(), redirectResponse{Redirect: "https://default.local"})
@@ -363,7 +365,7 @@ func (s *FirstFactorRedirectionSuite) TestShouldReply200WhenNoTargetURLProvidedA
 		"keepMeLoggedIn": false
 	}`)
 
-	FirstFactorPost(s.mock.Ctx)
+	FirstFactorPost(0, false)(s.mock.Ctx)
 
 	// Respond with 200.
 	s.mock.Assert200OK(s.T(), nil)
@@ -393,7 +395,7 @@ func (s *FirstFactorRedirectionSuite) TestShouldReply200WhenUnsafeTargetURLProvi
 		"keepMeLoggedIn": false
 	}`)
 
-	FirstFactorPost(s.mock.Ctx)
+	FirstFactorPost(0, false)(s.mock.Ctx)
 
 	// Respond with 200.
 	s.mock.Assert200OK(s.T(), nil)
@@ -403,3 +405,57 @@ func TestFirstFactorSuite(t *testing.T) {
 	suite.Run(t, new(FirstFactorSuite))
 	suite.Run(t, new(FirstFactorRedirectionSuite))
 }
+
+func TestFirstFactorDelayAverages(t *testing.T) {
+	execDuration := time.Millisecond * 500
+	oneSecond := time.Millisecond * 1000
+	durations := []time.Duration{oneSecond, oneSecond, oneSecond, oneSecond, oneSecond, oneSecond, oneSecond, oneSecond, oneSecond, oneSecond}
+	cursor := 0
+	mutex := &sync.Mutex{}
+	avgExecDuration := movingAverageIteration(execDuration, false, &cursor, &durations, mutex)
+	assert.Equal(t, avgExecDuration, float64(1000))
+
+	execDurations := []time.Duration{
+		time.Millisecond * 500, time.Millisecond * 500, time.Millisecond * 500, time.Millisecond * 500,
+		time.Millisecond * 500, time.Millisecond * 500, time.Millisecond * 500, time.Millisecond * 500,
+		time.Millisecond * 500, time.Millisecond * 500, time.Millisecond * 500, time.Millisecond * 500,
+	}
+
+	current := float64(1000)
+
+	// Execute at 500ms for 12 requests.
+	for _, execDuration = range execDurations {
+		// Should not dip below 500, and should decrease in value by 50 each iteration.
+		if current > 500 {
+			current -= 50
+		}
+
+		avgExecDuration := movingAverageIteration(execDuration, true, &cursor, &durations, mutex)
+		assert.Equal(t, avgExecDuration, current)
+	}
+}
+
+func TestFirstFactorDelayCalculations(t *testing.T) {
+	mock := mocks.NewMockAutheliaCtx(t)
+	successful := false
+
+	execDuration := 500 * time.Millisecond
+	avgExecDurationMs := 1000.0
+	expectedMinimumDelayMs := avgExecDurationMs - float64(execDuration.Milliseconds())
+
+	for i := 0; i < 100; i++ {
+		delay := calculateActualDelay(mock.Ctx, execDuration, avgExecDurationMs, &successful)
+		assert.True(t, delay >= expectedMinimumDelayMs)
+		assert.True(t, delay <= expectedMinimumDelayMs+float64(msMaximumRandomDelay))
+	}
+
+	execDuration = 5 * time.Millisecond
+	avgExecDurationMs = 5.0
+	expectedMinimumDelayMs = msMinimumDelay1FA - float64(execDuration.Milliseconds())
+
+	for i := 0; i < 100; i++ {
+		delay := calculateActualDelay(mock.Ctx, execDuration, avgExecDurationMs, &successful)
+		assert.True(t, delay >= expectedMinimumDelayMs)
+		assert.True(t, delay <= expectedMinimumDelayMs+float64(msMaximumRandomDelay))
+	}
+}

internal/server/server.go

@@ -47,7 +47,7 @@ func StartServer(configuration schema.Configuration, providers middlewares.Provi
 	router.GET("/api/verify", autheliaMiddleware(handlers.VerifyGet(configuration.AuthenticationBackend)))
 	router.HEAD("/api/verify", autheliaMiddleware(handlers.VerifyGet(configuration.AuthenticationBackend)))
 
-	router.POST("/api/firstfactor", autheliaMiddleware(handlers.FirstFactorPost))
+	router.POST("/api/firstfactor", autheliaMiddleware(handlers.FirstFactorPost(1000, true)))
 	router.POST("/api/logout", autheliaMiddleware(handlers.LogoutPost))
 
 	// Only register endpoints if forgot password is not disabled.

internal/suites/scenario_regulation_test.go

@@ -47,7 +47,7 @@ func (s *RegulationScenario) SetupTest() {
 }
 
 func (s *RegulationScenario) TestShouldBanUserAfterTooManyAttempt() {
-	ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
+	ctx, cancel := context.WithTimeout(context.Background(), 45*time.Second)
 	defer cancel()
 
 	s.doVisitLoginPage(ctx, s.T(), "")

internal/suites/suite_ldap.go

@@ -57,7 +57,7 @@ func init() {
 		SetUp:           setup,
 		SetUpTimeout:    5 * time.Minute,
 		OnSetupTimeout:  displayAutheliaLogs,
-		TestTimeout:     1 * time.Minute,
+		TestTimeout:     80 * time.Second,
 		TearDown:        teardown,
 		TearDownTimeout: 2 * time.Minute,
 		OnError:         displayAutheliaLogs,