[HOTFIX] Prevent Username Enumeration (#950)

* [HOTFIX] Prevent Username Enumeration

* thanks to TheHllm for identifying the bug: https://github.com/TheHllm
* temporarily prevents username enumeration with file auth
* proper calculated and very slightly random fix to come

* closely replicate behaviour

* allow error to bubble up

* Synchronize security documentation.

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

README.md

@@ -103,8 +103,9 @@ Authelia takes security very seriously. We follow the rule of
 [responsible disclosure](https://en.wikipedia.org/wiki/Responsible_disclosure), and we
 encourage the community to as well.
 
-Would you like to report any vulnerability discovered in Authelia, please first contact
-**clems4ever** on [Matrix](https://riot.im/app/#/room/#authelia:matrix.org) or by
+
+If you discover a vulnerability in Authelia, please first contact **clems4ever** on 
+[Matrix](https://riot.im/app/#/room/#authelia:matrix.org) or by
 [email](mailto:clement.michaud34@gmail.com).
 
 For details about security measures implemented in Authelia, please follow

SECURITY.md

@@ -4,8 +4,8 @@ Authelia takes security very seriously. We follow the rule of
 [responsible disclosure](https://en.wikipedia.org/wiki/Responsible_disclosure), and we
 encourage the community to as well.
 
-Would you like to report any vulnerability discovered in Authelia, please first contact
-**clems4ever** on [Matrix](https://riot.im/app/#/room/#authelia:matrix.org) or by
+If you discover a vulnerability in Authelia, please first contact **clems4ever** on 
+[Matrix](https://riot.im/app/#/room/#authelia:matrix.org) or by
 [email](mailto:clement.michaud34@gmail.com).
 
 For details about security measures implemented in Authelia, please follow

internal/authentication/file_user_provider.go

@@ -8,9 +8,11 @@ import (
 	"sync"
 
 	"github.com/asaskevich/govalidator"
+	"github.com/simia-tech/crypt"
 	"gopkg.in/yaml.v2"
 
 	"github.com/authelia/authelia/internal/configuration/schema"
+	"github.com/authelia/authelia/internal/utils"
 )
 
 // FileUserProvider is a provider reading details from a file.
@@ -18,6 +20,9 @@ type FileUserProvider struct {
 	configuration *schema.FileAuthenticationBackendConfiguration
 	database      *DatabaseModel
 	lock          *sync.Mutex
+
+	// TODO: Remove this. This is only here to temporarily fix the username enumeration security flaw in #949.
+	fakeHash string
 }
 
 // UserDetailsModel is the model of user details in the file database.
@@ -46,10 +51,23 @@ func NewFileUserProvider(configuration *schema.FileAuthenticationBackendConfigur
 		panic(err.Error())
 	}
 
+	// TODO: Remove this. This is only here to temporarily fix the username enumeration security flaw in #949.
+	// This generates a hash that should be usable to do a fake CheckUserPassword
+	algorithm := configuration.Password.Algorithm
+	if configuration.Password.Algorithm == "sha512" {
+		algorithm = HashingAlgorithmSHA512
+	}
+	settings := getCryptSettings(utils.RandomString(configuration.Password.SaltLength, HashingPossibleSaltCharacters),
+		algorithm, configuration.Password.Iterations, configuration.Password.Memory*1024, configuration.Password.Parallelism,
+		configuration.Password.KeyLength)
+	data := crypt.Base64Encoding.EncodeToString([]byte(utils.RandomString(configuration.Password.KeyLength, HashingPossibleSaltCharacters)))
+	fakeHash := fmt.Sprintf("%s$%s", settings, data)
+
 	return &FileUserProvider{
 		configuration: configuration,
 		database:      database,
 		lock:          &sync.Mutex{},
+		fakeHash:      fakeHash,
 	}
 }
 
@@ -95,7 +113,12 @@ func (p *FileUserProvider) CheckUserPassword(username string, password string) (
 		}
 		return ok, nil
 	}
-	return false, fmt.Errorf("User '%s' does not exist in database", username)
+
+	// TODO: Remove this. This is only here to temporarily fix the username enumeration security flaw in #949.
+	hashedPassword := strings.ReplaceAll(p.fakeHash, "{CRYPT}", "")
+	_, err := CheckPassword(password, hashedPassword)
+
+	return false, err
 }
 
 // GetDetails retrieve the groups a user belongs to.

internal/authentication/file_user_provider_test.go

@@ -68,14 +68,26 @@ func TestShouldCheckUserPasswordIsWrong(t *testing.T) {
 	})
 }
 
-func TestShouldCheckUserPasswordOfUnexistingUser(t *testing.T) {
+func TestShouldCheckUserPasswordIsWrongForEnumerationCompare(t *testing.T) {
 	WithDatabase(UserDatabaseContent, func(path string) {
 		config := DefaultFileAuthenticationBackendConfiguration
 		config.Path = path
 		provider := NewFileUserProvider(&config)
-		_, err := provider.CheckUserPassword("fake", "password")
-		assert.Error(t, err)
-		assert.Equal(t, "User 'fake' does not exist in database", err.Error())
+
+		ok, err := provider.CheckUserPassword("enumeration", "wrong_password")
+		assert.NoError(t, err)
+		assert.False(t, ok)
+	})
+}
+
+func TestShouldCheckUserPasswordOfUserThatDoesNotExist(t *testing.T) {
+	WithDatabase(UserDatabaseContent, func(path string) {
+		config := DefaultFileAuthenticationBackendConfiguration
+		config.Path = path
+		provider := NewFileUserProvider(&config)
+		ok, err := provider.CheckUserPassword("fake", "password")
+		assert.NoError(t, err)
+		assert.Equal(t, false, ok)
 	})
 }
 
@@ -257,6 +269,11 @@ users:
   james:
     password: "{CRYPT}$6$rounds=500000$jgiCMRyGXzoqpxS3$w2pJeZnnH8bwW3zzvoMWtTRfQYsHbWbD/hquuQ5vUeIyl9gdwBIt6RWk2S6afBA0DPakbeWgD/4SZPiS0hYtU/"
     email: james.dean@authelia.com
+
+
+  enumeration:
+    password: "$argon2id$v=19$m=131072,p=8$BpLnfgDsc2WD8F2q$O126GHPeZ5fwj7OLSs7PndXsTbje76R+QW9/EGfhkJg"
+    email: james.dean@authelia.com
 `)
 
 var MalformedUserDatabaseContent = []byte(`

internal/authentication/ldap_user_provider.go

@@ -48,7 +48,7 @@ func (p *LDAPUserProvider) connect(userDN string, password string) (LDAPConnecti
 	if url.Scheme == "ldaps" {
 		logging.Logger().Trace("LDAP client starts a TLS session")
 		conn, err := p.connectionFactory.DialTLS("tcp", url.Host, &tls.Config{
-			InsecureSkipVerify: p.configuration.SkipVerify,
+			InsecureSkipVerify: p.configuration.SkipVerify, //nolint:gosec
 		})
 		if err != nil {
 			return nil, err

internal/authentication/password_hash.go

@@ -127,11 +127,7 @@ func HashPassword(password, salt, algorithm string, iterations, memory, parallel
 	if salt == "" {
 		salt = utils.RandomString(saltLength, HashingPossibleSaltCharacters)
 	}
-	if algorithm == HashingAlgorithmArgon2id {
-		settings, _ = crypt.Argon2idSettings(memory, iterations, parallelism, keyLength, salt)
-	} else if algorithm == HashingAlgorithmSHA512 {
-		settings = fmt.Sprintf("$6$rounds=%d$%s", iterations, salt)
-	}
+	settings = getCryptSettings(salt, algorithm, iterations, memory, parallelism, keyLength)
 
 	// This error can be ignored because we check for it before a user gets here
 	hash, _ = crypt.Crypt(password, settings)
@@ -150,3 +146,14 @@ func CheckPassword(password, hash string) (ok bool, err error) {
 	}
 	return hash == expectedHash, nil
 }
+
+func getCryptSettings(salt, algorithm string, iterations, memory, parallelism, keyLength int) (settings string) {
+	if algorithm == HashingAlgorithmArgon2id {
+		settings, _ = crypt.Argon2idSettings(memory, iterations, parallelism, keyLength, salt)
+	} else if algorithm == HashingAlgorithmSHA512 {
+		settings = fmt.Sprintf("$6$rounds=%d$%s", iterations, salt)
+	} else {
+		panic("invalid password hashing algorithm provided")
+	}
+	return settings
+}