diff --git a/data/web/inc/functions.inc.php b/data/web/inc/functions.inc.php
index 79bc97b24..ab149b60a 100644
--- a/data/web/inc/functions.inc.php
+++ b/data/web/inc/functions.inc.php
@@ -1857,6 +1857,40 @@ function get_tfa($username = null, $id = null) {
     }
 }
 function verify_tfa_login($username, $_data) {
+  global $redis;
+  global $TFA_MAX_FAILS;
+  global $TFA_FAIL_WINDOW;
+
+  if (empty($username)) {
+    return false;
+  }
+  // Count failed second factors per account, so codes cannot be guessed from many addresses
+  $fails_key = 'TFA_FAILS_' . $username;
+  if (intval($redis->get($fails_key)) >= $TFA_MAX_FAILS) {
+    $_SESSION['return'][] =  array(
+      'type' => 'danger',
+      'log' => array(__FUNCTION__, $username, '*'),
+      'msg' => 'tfa_login_locked'
+    );
+    $verified = false;
+  }
+  else {
+    $verified = verify_tfa_token($username, $_data);
+  }
+  if ($verified !== true) {
+    // The window starts with the first failure and is not extended by further attempts
+    if ($redis->incr($fails_key) == 1) {
+      $redis->expire($fails_key, $TFA_FAIL_WINDOW);
+    }
+    // Same message format as failed passwords, so the default fail2ban rule counts it
+    error_log("mailcow UI: Invalid password for " . $username . " (second factor) by " . $_SERVER['REMOTE_ADDR']);
+    $redis->publish("F2B_CHANNEL", "mailcow UI: Invalid password for " . $username . " (second factor) by " . $_SERVER['REMOTE_ADDR']);
+    return false;
+  }
+  $redis->del($fails_key);
+  return true;
+}
+function verify_tfa_token($username, $_data) {
   global $pdo;
   global $yubi;
   global $u2f;
diff --git a/data/web/inc/vars.inc.php b/data/web/inc/vars.inc.php
index 451704565..32f6f6645 100644
--- a/data/web/inc/vars.inc.php
+++ b/data/web/inc/vars.inc.php
@@ -169,6 +169,12 @@ $SESSION_NAME = "MCSESSID";
 // Label for OTP devices
 $OTP_LABEL = "mailcow UI";
 
+// Failed second factor logins (TOTP, Yubico OTP, WebAuthn) of an account before its second factor is locked
+$TFA_MAX_FAILS = 10;
+
+// Time (in s) from the first failed second factor login until the counter and the lock are reset
+$TFA_FAIL_WINDOW = 900;
+
 // How long to wait (in s) for cURL Docker requests
 $DOCKER_TIMEOUT = 60;
 
diff --git a/data/web/lang/lang.de-de.json b/data/web/lang/lang.de-de.json
index ca9a093b8..23dfd5c05 100644
--- a/data/web/lang/lang.de-de.json
+++ b/data/web/lang/lang.de-de.json
@@ -641,6 +641,7 @@
         "temp_error": "Temporärer Fehler",
         "text_empty": "Text darf nicht leer sein",
         "tfa_token_invalid": "TFA-Token ungültig",
+        "tfa_login_locked": "Zu viele fehlgeschlagene Zwei-Faktor-Anmeldungen, bitte später erneut versuchen",
         "tfa_removal_blocked": "Zwei-Faktor-Authentifizierung kann nicht entfernt werden, da sie für Ihr Konto erforderlich ist.",
         "tls_policy_map_dest_invalid": "Ziel ist ungültig",
         "tls_policy_map_entry_exists": "Eine TLS-Richtlinie \"%s\" existiert bereits",
diff --git a/data/web/lang/lang.en-gb.json b/data/web/lang/lang.en-gb.json
index 7ba74740f..dc13af0a6 100644
--- a/data/web/lang/lang.en-gb.json
+++ b/data/web/lang/lang.en-gb.json
@@ -517,6 +517,7 @@
         "group_send_as_invalid": "Send-as address %s is invalid or unknown",
         "iam_sync_mode_invalid": "Invalid sync mode",
         "iam_sync_unavailable": "The identity provider cannot be synced (Keycloak and LDAP only)",
+        "tfa_login_locked": "Too many failed two-factor logins, please try again later",
         "tfa_removal_blocked": "Two-factor authentication cannot be removed because it is required for your account.",
         "alias_domain_invalid": "Alias domain %s is invalid",
         "alias_empty": "Alias address must not be empty",