fix(session): use crypto/rand for session id generator (#2594)

This adjusts the session ID generator making it use it's own random function rather than using one from the utils lib. This allows us to utilize crypto/rand or math/rand interchangeably. Additionally refactor the utils.RandomString func.

internal/authentication/const.go

@@ -60,7 +60,7 @@ const (
 )
 
 // HashingPossibleSaltCharacters represents valid hashing runes.
-var HashingPossibleSaltCharacters = []rune("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789+/")
+var HashingPossibleSaltCharacters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789+/"
 
 // ErrUserNotFound indicates the user wasn't found in the authentication backend.
 var ErrUserNotFound = errors.New("user not found")

internal/authentication/password_hash.go

@@ -126,7 +126,7 @@ func HashPassword(password, salt string, algorithm CryptAlgo, iterations, memory
 	}
 
 	if salt == "" {
-		salt = crypt.Base64Encoding.EncodeToString([]byte(utils.RandomString(saltLength, HashingPossibleSaltCharacters)))
+		salt = crypt.Base64Encoding.EncodeToString(utils.RandomBytes(saltLength, HashingPossibleSaltCharacters, true))
 	}
 
 	settings = getCryptSettings(salt, algorithm, iterations, memory, parallelism, keyLength)

internal/authentication/password_hash_test.go

@@ -58,8 +58,7 @@ func TestArgon2idHashSaltValidValues(t *testing.T) {
 
 	var hash string
 
-	data := string(HashingPossibleSaltCharacters)
-	datas := utils.SliceString(data, 16)
+	datas := utils.SliceString(HashingPossibleSaltCharacters, 16)
 
 	for _, salt := range datas {
 		hash, err = HashPassword("password", salt, HashingAlgorithmArgon2id, 1, 8, 1, 32, 16)
@@ -74,8 +73,7 @@ func TestSHA512HashSaltValidValues(t *testing.T) {
 
 	var hash string
 
-	data := string(HashingPossibleSaltCharacters)
-	datas := utils.SliceString(data, 16)
+	datas := utils.SliceString(HashingPossibleSaltCharacters, 16)
 
 	for _, salt := range datas {
 		hash, err = HashPassword("password", salt, HashingAlgorithmSHA512, 1000, 0, 0, 0, 16)

internal/notification/smtp_notifier.go

@@ -133,7 +133,7 @@ func (n *SMTPNotifier) compose(recipient, subject, body, htmlBody string) error
 		return err
 	}
 
-	boundary := utils.RandomString(30, utils.AlphaNumericCharacters)
+	boundary := utils.RandomString(30, utils.AlphaNumericCharacters, true)
 
 	now := time.Now()
 

internal/server/template.go

@@ -13,8 +13,6 @@ import (
 	"github.com/authelia/authelia/v4/internal/utils"
 )
 
-var alphaNumericRunes = []rune("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789")
-
 // ServeTemplatedFile serves a templated version of a specified file,
 // this is utilised to pass information between the backend and frontend
 // and generate a nonce to support a restrictive CSP while using material-ui.
@@ -55,7 +53,7 @@ func ServeTemplatedFile(publicDir, file, rememberMe, resetPassword, session, the
 		}
 
 		baseURL := scheme + "://" + string(ctx.Request.Host()) + base + "/"
-		nonce := utils.RandomString(32, alphaNumericRunes)
+		nonce := utils.RandomString(32, utils.AlphaNumericCharacters, true)
 
 		switch extension := filepath.Ext(file); extension {
 		case ".html":

internal/session/const.go

@@ -1,8 +1,13 @@
 package session
 
-const userSessionStorerKey = "UserSession"
+const (
+	testDomain     = "example.com"
+	testExpiration = "40"
+	testName       = "my_session"
+	testUsername   = "john"
+)
 
-const testDomain = "example.com"
-const testExpiration = "40"
-const testName = "my_session"
-const testUsername = "john"
+const (
+	userSessionStorerKey = "UserSession"
+	randomSessionChars   = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-_!#$%^*"
+)

internal/session/provider_config.go

@@ -1,6 +1,7 @@
 package session
 
 import (
+	"crypto/rand"
 	"crypto/tls"
 	"crypto/x509"
 	"fmt"
@@ -20,7 +21,15 @@ func NewProviderConfig(configuration schema.SessionConfiguration, certPool *x509
 	config := session.NewDefaultConfig()
 
 	config.SessionIDGeneratorFunc = func() []byte {
-		return []byte(utils.RandomString(30, utils.AlphaNumericCharacters))
+		bytes := make([]byte, 32)
+
+		_, _ = rand.Read(bytes)
+
+		for i, b := range bytes {
+			bytes[i] = randomSessionChars[b%byte(len(randomSessionChars))]
+		}
+
+		return bytes
 	}
 
 	// Override the cookie name.
@@ -47,7 +56,6 @@ func NewProviderConfig(configuration schema.SessionConfiguration, certPool *x509
 	// Ignore the error as it will be handled by validator.
 	config.Expiration, _ = utils.ParseDurationString(configuration.Expiration)
 
-	// TODO(c.michaud): Make this configurable by giving the list of IPs that are trustable.
 	config.IsSecureFunc = func(*fasthttp.RequestCtx) bool {
 		return true
 	}

internal/utils/const.go

@@ -56,8 +56,10 @@ var (
 	reDuration = regexp.MustCompile(`^(?P<Duration>[1-9]\d*?)(?P<Unit>[smhdwMy])?$`)
 )
 
+var (
 	// AlphaNumericCharacters are literally just valid alphanumeric chars.
-var AlphaNumericCharacters = []rune("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789")
+	AlphaNumericCharacters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
+)
 
 var htmlEscaper = strings.NewReplacer(
 	"&", "&amp;",

internal/utils/hashing_test.go

@@ -23,7 +23,7 @@ func TestShouldHashString(t *testing.T) {
 	assert.Equal(t, "ae448ac86c4e8e4dec645729708ef41873ae79c6dff84eff73360989487f08e5", anotherSum)
 	assert.NotEqual(t, sum, anotherSum)
 
-	randomInput := RandomString(40, AlphaNumericCharacters)
+	randomInput := RandomString(40, AlphaNumericCharacters, false)
 	randomSum := HashSHA256FromString(randomInput)
 
 	assert.NotEqual(t, randomSum, sum)
@@ -40,7 +40,7 @@ func TestShouldHashPath(t *testing.T) {
 	err = os.WriteFile(filepath.Join(dir, "anotherfile"), []byte("another\n"), 0600)
 	assert.NoError(t, err)
 
-	err = os.WriteFile(filepath.Join(dir, "randomfile"), []byte(RandomString(40, AlphaNumericCharacters)+"\n"), 0600)
+	err = os.WriteFile(filepath.Join(dir, "randomfile"), []byte(RandomString(40, AlphaNumericCharacters, true)+"\n"), 0600)
 	assert.NoError(t, err)
 
 	sum, err := HashSHA256FromPath(filepath.Join(dir, "myfile"))

internal/utils/strings.go

@@ -1,6 +1,7 @@
 package utils
 
 import (
+	crand "crypto/rand"
 	"fmt"
 	"math/rand"
 	"net/url"
@@ -139,19 +140,37 @@ func StringSlicesDelta(before, after []string) (added, removed []string) {
 	return added, removed
 }
 
-// RandomString generate a random string of n characters.
-func RandomString(n int, characters []rune) (randomString string) {
-	rand.Seed(time.Now().UnixNano())
-
-	b := make([]rune, n)
-	for i := range b {
-		b[i] = characters[rand.Intn(len(characters))] //nolint:gosec // Likely isn't necessary to use the more expensive crypto/rand for this utility func.
+// RandomString returns a random string with a given length with values from the provided characters. When crypto is set
+// to false we use math/rand and when it's set to true we use crypto/rand. The crypto option should always be set to true
+// excluding when the task is time sensitive and would not benefit from extra randomness.
+func RandomString(n int, characters string, crypto bool) (randomString string) {
+	return string(RandomBytes(n, characters, crypto))
 }
 
-	return string(b)
+// RandomBytes returns a random []byte with a given length with values from the provided characters. When crypto is set
+// to false we use math/rand and when it's set to true we use crypto/rand. The crypto option should always be set to true
+// excluding when the task is time sensitive and would not benefit from extra randomness.
+func RandomBytes(n int, characters string, crypto bool) (bytes []byte) {
+	bytes = make([]byte, n)
+
+	if crypto {
+		_, _ = crand.Read(bytes)
+	} else {
+		_, _ = rand.Read(bytes) //nolint:gosec // As this is an option when using this function it's not necessary to be concerned about this.
+	}
+
+	for i, b := range bytes {
+		bytes[i] = characters[b%byte(len(characters))]
+	}
+
+	return bytes
 }
 
 // StringHTMLEscape escapes chars for a HTML body.
 func StringHTMLEscape(input string) (output string) {
 	return htmlEscaper.Replace(input)
 }
+
+func init() {
+	rand.Seed(time.Now().UnixNano())
+}

internal/utils/strings_test.go

@@ -7,6 +7,17 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
+func TestShouldNotGenerateSameRandomString(t *testing.T) {
+	randomStringOne := RandomString(10, AlphaNumericCharacters, false)
+	randomStringTwo := RandomString(10, AlphaNumericCharacters, false)
+
+	randomCryptoStringOne := RandomString(10, AlphaNumericCharacters, true)
+	randomCryptoStringTwo := RandomString(10, AlphaNumericCharacters, true)
+
+	assert.NotEqual(t, randomStringOne, randomStringTwo)
+	assert.NotEqual(t, randomCryptoStringOne, randomCryptoStringTwo)
+}
+
 func TestShouldDetectAlphaNumericString(t *testing.T) {
 	assert.True(t, IsStringAlphaNumeric("abc"))
 	assert.True(t, IsStringAlphaNumeric("abc123"))