From 7ae7df0a110b978a2ddfe0a423569995a3902878 Mon Sep 17 00:00:00 2001
From: janis steiner <janis@jakach.ch>
Date: Wed, 6 May 2026 08:51:51 +0200
Subject: [PATCH] fixing some security issues and harderning service

---
 app-code/account/index.php                   |   4 +-
 app-code/api/account/get_user_data.php       |   7 +-
 app-code/api/account/update_2fa.php          |  17 ++-
 app-code/api/account/update_message.php      |  17 ++-
 app-code/api/account/update_passkey.php      |   5 +-
 app-code/api/account/update_pw.php           |  14 +-
 app-code/api/account/update_user_data.php    |  21 +--
 app-code/api/auth/check_auth_key.php         |   7 +-
 app-code/api/login/check_mfa.php             |   9 +-
 app-code/api/login/check_passkey.php         |   6 +-
 app-code/api/login/check_pw.php              |   9 +-
 app-code/api/login/delete_keepmeloggedin.php |   5 +-
 app-code/api/login/keepmeloggedin.php        |  16 ++-
 app-code/api/login/redirect.php              |  14 +-
 app-code/api/login/send_reset_link.php       |  23 +++-
 app-code/api/login/set_username.php          |   8 +-
 app-code/api/manage/delete_user.php          |   6 +-
 app-code/api/manage/fetch_users.php          |   5 +-
 app-code/api/register/register_user.php      |  30 ++++-
 app-code/api/utils/check_keepmeloggedin.php  |   8 +-
 app-code/api/utils/security.php              | 128 +++++++++++++++++++
 app-code/index.php                           |  32 ++---
 app-code/login/account_selector.php          |  10 +-
 app-code/login/keepmeloggedin.php            |   6 +-
 app-code/login/logout.php                    |   5 +-
 app-code/login/mfa.php                       |   6 +-
 app-code/login/passkey.php                   |   6 +-
 app-code/login/pw.php                        |   6 +-
 app-code/plugins/auth.php                    |  11 +-
 app-code/register/index.php                  |  11 +-
 30 files changed, 328 insertions(+), 124 deletions(-)
 create mode 100644 app-code/api/utils/security.php

diff --git a/app-code/account/index.php b/app-code/account/index.php
index cef2d9d..228669d 100644
--- a/app-code/account/index.php
+++ b/app-code/account/index.php
@@ -1,5 +1,6 @@
 <?php
-session_start();
+include "../api/utils/security.php";
+secure_session_start();
 
 // Check if the user is logged in
 if (!isset($_SESSION["logged_in"]) || $_SESSION["logged_in"] !== true) {
@@ -625,4 +626,3 @@ function generate2FAQRCode(issuer, accountName, secret) {
 
 </body>
 </html>
-
diff --git a/app-code/api/account/get_user_data.php b/app-code/api/account/get_user_data.php
index bc4d6e9..b5d0a1e 100644
--- a/app-code/api/account/get_user_data.php
+++ b/app-code/api/account/get_user_data.php
@@ -1,13 +1,14 @@
 <?php
 // Simulate fetching user data from a database
-session_start();
+include "../utils/security.php";
+secure_session_start();
 header('Content-Type: application/json');
-if($_SESSION["logged_in"]!==true){
+if(!isset($_SESSION["logged_in"]) || $_SESSION["logged_in"]!==true){
 	$data=[
 		'status' => 'error',
 		'message' => 'not logged in'
 	];
-	echo json_encode($user_data);
+	echo json_encode($data);
 	exit();
 }
 
diff --git a/app-code/api/account/update_2fa.php b/app-code/api/account/update_2fa.php
index a3b337e..288e85e 100644
--- a/app-code/api/account/update_2fa.php
+++ b/app-code/api/account/update_2fa.php
@@ -1,15 +1,11 @@
 <?php
-session_start();
+include "../utils/security.php";
+secure_session_start();
+require_same_origin_request();
 header('Content-Type: application/json');
 
 // Check if the user is logged in
-if (!isset($_SESSION["logged_in"]) || $_SESSION["logged_in"] !== true) {
-    echo json_encode([
-        'success' => false,
-        'message' => 'Not logged in'
-    ]);
-    exit();
-}
+require_logged_in();
 
 // Include database configuration
 include "../../config/config.php";
@@ -34,6 +30,10 @@ $username = $_SESSION["username"];
 
 // Get the raw POST data (JSON)
 $data = json_decode(file_get_contents("php://input"));
+if(!isset($data->enable_2fa) || !is_bool($data->enable_2fa)){
+	echo json_encode(['success' => false, 'message' => 'Missing required fields.']);
+	exit();
+}
 if($data->enable_2fa==true){
 	//create 2fa secret key
 	$twofa_secret=generateBase32Secret();
@@ -68,4 +68,3 @@ if($data->enable_2fa==false){
 }
 
 ?>
-
diff --git a/app-code/api/account/update_message.php b/app-code/api/account/update_message.php
index 31e2f0a..5f881a4 100644
--- a/app-code/api/account/update_message.php
+++ b/app-code/api/account/update_message.php
@@ -1,15 +1,11 @@
 <?php
-session_start();
+include "../utils/security.php";
+secure_session_start();
+require_same_origin_request();
 header('Content-Type: application/json');
 
 // Check if the user is logged in
-if (!isset($_SESSION["logged_in"]) || $_SESSION["logged_in"] !== true) {
-    echo json_encode([
-        'success' => false,
-        'message' => 'Not logged in'
-    ]);
-    exit();
-}
+require_logged_in();
 
 // Include database configuration
 include "../../config/config.php";
@@ -32,6 +28,10 @@ $username = $_SESSION["username"];
 
 // Get the raw POST data (JSON)
 $data = json_decode(file_get_contents("php://input"));
+if(!isset($data->enable_message) || !is_bool($data->enable_message)){
+	echo json_encode(['success' => false, 'message' => 'Missing required fields.']);
+	exit();
+}
 if($data->enable_message==true){
 	$sql="UPDATE users SET login_message=1 WHERE id = ?";
 	if ($update_stmt = $conn->prepare($sql)) {
@@ -64,4 +64,3 @@ if($data->enable_message==false){
 }
 
 ?>
-
diff --git a/app-code/api/account/update_passkey.php b/app-code/api/account/update_passkey.php
index bc3c6f0..cfdd109 100644
--- a/app-code/api/account/update_passkey.php
+++ b/app-code/api/account/update_passkey.php
@@ -3,6 +3,9 @@
 header('Content-Type: application/json');
 
 
+include "../utils/security.php";
+secure_session_start();
+require_same_origin_request();
 
 require_once 'WebAuthn.php';
 
@@ -15,7 +18,6 @@ if ($conn->connect_error) {
 }
 
 try {
-	session_start();
 	if (!isset($_SESSION["logged_in"]) || $_SESSION["logged_in"] !== true) {
     echo json_encode([
         'success' => false,
@@ -168,4 +170,3 @@ try {
     print(json_encode($return));
 }
 ?>
-
diff --git a/app-code/api/account/update_pw.php b/app-code/api/account/update_pw.php
index 1733244..c3e14f9 100644
--- a/app-code/api/account/update_pw.php
+++ b/app-code/api/account/update_pw.php
@@ -1,15 +1,11 @@
 <?php
-session_start();
+include "../utils/security.php";
+secure_session_start();
+require_same_origin_request();
 header('Content-Type: application/json');
 
 // Check if the user is logged in
-if (!isset($_SESSION["logged_in"]) || $_SESSION["logged_in"] !== true) {
-    echo json_encode([
-        'success' => false,
-        'message' => 'Not logged in'
-    ]);
-    exit();
-}
+require_logged_in();
 
 // Include database configuration
 include "../../config/config.php";
@@ -36,7 +32,6 @@ $data = json_decode(file_get_contents("php://input"));
 // Check if the required fields are present
 if (isset($data->old_password) && isset($data->new_password)) {
     // Get the user ID (this should be taken from the session or JWT token)
-    session_start();
     $user_id = $_SESSION['id']; // Assuming user_id is stored in session
 
     // Sanitize inputs
@@ -95,4 +90,3 @@ if (isset($data->old_password) && isset($data->new_password)) {
     echo json_encode(['success' => false, 'message' => 'Missing required fields.']);
 }
 ?>
-
diff --git a/app-code/api/account/update_user_data.php b/app-code/api/account/update_user_data.php
index aa26a6a..bcb782e 100644
--- a/app-code/api/account/update_user_data.php
+++ b/app-code/api/account/update_user_data.php
@@ -1,15 +1,11 @@
 <?php
-session_start();
+include "../utils/security.php";
+secure_session_start();
+require_same_origin_request();
 header('Content-Type: application/json');
 
 // Check if the user is logged in
-if (!isset($_SESSION["logged_in"]) || $_SESSION["logged_in"] !== true) {
-    echo json_encode([
-        'success' => false,
-        'message' => 'Not logged in'
-    ]);
-    exit();
-}
+require_logged_in();
 
 // Include database configuration
 include "../../config/config.php";
@@ -47,7 +43,14 @@ if ($_SERVER['REQUEST_METHOD'] === 'POST') {
 
     // Sanitize and validate the input
     $name = preg_replace("/[^a-zA-Z0-9_]/", "", $data['name']); // Allow only letters, numbers, and underscores
-    $email = filter_var($data['email'], FILTER_SANITIZE_EMAIL); // Sanitize email
+    $email = trim((string) $data['email']);
+    if ($email !== "" && !filter_var($email, FILTER_VALIDATE_EMAIL)) {
+        echo json_encode([
+            'success' => false,
+            'message' => 'Invalid email address'
+        ]);
+        exit();
+    }
     $telegram_id = htmlspecialchars($data['telegram_id'], ENT_QUOTES, 'UTF-8'); // Escape special characters
 
     //check if username is allready taken
diff --git a/app-code/api/auth/check_auth_key.php b/app-code/api/auth/check_auth_key.php
index de0d29f..1543958 100644
--- a/app-code/api/auth/check_auth_key.php
+++ b/app-code/api/auth/check_auth_key.php
@@ -2,14 +2,14 @@
 header('Content-Type: application/json');
 include "../../config/config.php";
 $conn = new mysqli($DB_SERVERNAME, $DB_USERNAME, $DB_PASSWORD, $DB_DATABASE);
+$now=time();
 $sql="DELETE FROM auth_tokens WHERE valid_until < ?;";
 $stmt = mysqli_prepare($conn, $sql);
 mysqli_stmt_bind_param($stmt, 'i',$now);
 mysqli_stmt_execute($stmt);
 mysqli_stmt_close($stmt);
 
-$auth_key=$_GET["auth_token"];
-$now=time();
+$auth_key=$_GET["auth_token"] ?? "";
 $sql="SELECT user_id FROM auth_tokens WHERE auth_token = ? AND valid_until > ?;";
 $stmt = mysqli_prepare($conn, $sql);
 mysqli_stmt_bind_param($stmt, 'si', $auth_key,$now);
@@ -54,8 +54,7 @@ if(mysqli_stmt_num_rows($stmt) == 1){
 }else{
 	$data=[
 		'status' => 'failure',
-		'msg'=>'invalid auth key',
-		'auth_key'=>$auth_key
+		'msg'=>'invalid auth key'
 	];
 	echo(json_encode($data));
 }
diff --git a/app-code/api/login/check_mfa.php b/app-code/api/login/check_mfa.php
index 3911fac..11d9c22 100644
--- a/app-code/api/login/check_mfa.php
+++ b/app-code/api/login/check_mfa.php
@@ -1,5 +1,7 @@
 <?php
-session_start();
+include "../utils/security.php";
+secure_session_start();
+require_same_origin_request();
 header('Content-Type: application/json');
 $send_to=$_SESSION["end_url"];
 
@@ -17,10 +19,11 @@ $twofa_secret="";
 mysqli_stmt_bind_result($stmt, $twofa_secret);
 mysqli_stmt_fetch($stmt);
 mysqli_stmt_close($stmt);
-$twofa_pin=$_POST["twofa_pin"];
+$twofa_pin=$_POST["twofa_pin"] ?? "";
 
-if(generateTOTP($twofa_secret)===$twofa_pin){
+if($twofa_secret !== "" && hash_equals(generateTOTP($twofa_secret), $twofa_pin)){
 	$_SESSION["mfa_authenticated"]=1;
+	session_regenerate_id(true);
 	$data = [
 		'status' => 'success'
 	];
diff --git a/app-code/api/login/check_passkey.php b/app-code/api/login/check_passkey.php
index 1f286f5..f2f2c8b 100644
--- a/app-code/api/login/check_passkey.php
+++ b/app-code/api/login/check_passkey.php
@@ -1,5 +1,8 @@
 <?php
 header('Content-Type: application/json');
+include "../utils/security.php";
+secure_session_start();
+require_same_origin_request();
 require_once 'WebAuthn.php';
 include "../../config/config.php";
 $conn = new mysqli($DB_SERVERNAME, $DB_USERNAME, $DB_PASSWORD,$DB_DATABASE);
@@ -9,8 +12,6 @@ if ($conn->connect_error) {
 }
 
 try {
-    session_start();
-
     // read get argument and post body
     $fn = filter_input(INPUT_GET, 'fn');
     $requireResidentKey = !!filter_input(INPUT_GET, 'requireResidentKey');
@@ -144,6 +145,7 @@ try {
 		$_SESSION["mfa_authenticated"]=1;
 		$_SESSION["pw_authenticated"]=1;
 		$_SESSION["passkey_authenticated"]=1;
+		session_regenerate_id(true);
 		$return = new stdClass();
 		$return->success = true;
 		
diff --git a/app-code/api/login/check_pw.php b/app-code/api/login/check_pw.php
index 45fe688..721cd2c 100644
--- a/app-code/api/login/check_pw.php
+++ b/app-code/api/login/check_pw.php
@@ -1,5 +1,7 @@
 <?php
-session_start();
+include "../utils/security.php";
+secure_session_start();
+require_same_origin_request();
 header('Content-Type: application/json');
 $send_to=$_SESSION["end_url"];
 
@@ -17,10 +19,11 @@ $pepper="";
 mysqli_stmt_bind_result($stmt, $pw,$pepper);
 mysqli_stmt_fetch($stmt);
 mysqli_stmt_close($stmt);
-$password=$_POST["password"];
+$password=$_POST["password"] ?? "";
 
-if(password_verify($password.$pepper,$pw)){
+if($pw !== "" && password_verify($password.$pepper,$pw)){
 	$_SESSION["pw_authenticated"]=1;
+	session_regenerate_id(true);
 	$data = [
 		'status' => 'success'
 	];
diff --git a/app-code/api/login/delete_keepmeloggedin.php b/app-code/api/login/delete_keepmeloggedin.php
index 800a08d..6c142bc 100644
--- a/app-code/api/login/delete_keepmeloggedin.php
+++ b/app-code/api/login/delete_keepmeloggedin.php
@@ -1,7 +1,10 @@
 <?php
-session_start();
+include "../utils/security.php";
+secure_session_start();
+require_same_origin_request();
 header('Content-Type: application/json');
 $send_to=$_SESSION["end_url"];
+require_logged_in();
 
 include "../../config/config.php";
 $conn = new mysqli($DB_SERVERNAME, $DB_USERNAME, $DB_PASSWORD, $DB_DATABASE);
diff --git a/app-code/api/login/keepmeloggedin.php b/app-code/api/login/keepmeloggedin.php
index c014627..49b3eed 100644
--- a/app-code/api/login/keepmeloggedin.php
+++ b/app-code/api/login/keepmeloggedin.php
@@ -1,24 +1,30 @@
 <?php
-session_start();
+include "../utils/security.php";
+secure_session_start();
+require_same_origin_request();
 header('Content-Type: application/json');
 $send_to=$_SESSION["end_url"];
 
 include "../../config/config.php";
 $conn = new mysqli($DB_SERVERNAME, $DB_USERNAME, $DB_PASSWORD, $DB_DATABASE);
-$keepmeloggedin=$_POST["keepmeloggedin"];
+$keepmeloggedin=$_POST["keepmeloggedin"] ?? "false";
 if($keepmeloggedin=="true"){
+	if (empty($_SESSION["id"]) || empty($_SESSION["pw_authenticated"]) || empty($_SESSION["mfa_authenticated"])) {
+		json_response(['status' => 'failure', 'message' => 'Not fully authenticated'], 401);
+	}
 	$_SESSION["keepmeloggedin_asked"]=true;
 	$user_id=$_SESSION["id"];
 	
 	//create a login token
 	$login_token=bin2hex(random_bytes(128));
-	$agent=$_SERVER['HTTP_USER_AGENT'];
+	$login_token_hash=remember_token_hash($login_token);
+	$agent=$_SERVER['HTTP_USER_AGENT'] ?? "";
 	$sql="INSERT INTO keepmeloggedin (auth_token,user_id,agent) VALUES (?,?,?);";
 	$stmt = mysqli_prepare($conn, $sql);
-	mysqli_stmt_bind_param($stmt, 'sis', $login_token,$user_id,$agent);
+	mysqli_stmt_bind_param($stmt, 'sis', $login_token_hash,$user_id,$agent);
 	mysqli_stmt_execute($stmt);
 	mysqli_stmt_close($stmt);
-	setcookie("auth_token", $login_token, time() + (30 * 24 * 60 * 60), "/", "", true, true);
+	set_secure_cookie("auth_token", $login_token, time() + (30 * 24 * 60 * 60));
 	$data = [
 		'status' => 'success'
 	];
diff --git a/app-code/api/login/redirect.php b/app-code/api/login/redirect.php
index 8795fe4..8ce7311 100644
--- a/app-code/api/login/redirect.php
+++ b/app-code/api/login/redirect.php
@@ -1,11 +1,12 @@
 <?php
-session_start();
+include "../utils/security.php";
+secure_session_start();
 header('Content-Type: application/json');
 
 include "../utils/get_location.php";
 
-$send_to=$_SESSION["end_url"];
-$send_to = htmlspecialchars(str_replace([';', 'script', 'java','(',')'],'',$send_to));
+$send_to=normalize_redirect_target($_SESSION["end_url"] ?? "/account/");
+$_SESSION["end_url"] = $send_to;
 include "../../config/config.php";
 $conn = new mysqli($DB_SERVERNAME, $DB_USERNAME, $DB_PASSWORD, $DB_DATABASE);
 
@@ -56,7 +57,7 @@ else if ($_SESSION["needs_auth"]===false && $_SESSION["mfa_authenticated"]==1 &&
 	if(!empty($send_to)){
 		$data=[
 		        'message' => 'done',
-		        'redirect' => $send_to."?auth=$auth_token"
+		        'redirect' => append_auth_token_to_redirect($send_to, $auth_token)
 		];
 	}else{
 		$data=[
@@ -65,7 +66,8 @@ else if ($_SESSION["needs_auth"]===false && $_SESSION["mfa_authenticated"]==1 &&
 		];
 	}
 	//update last login
-	$ip=trim(explode(",",$_SERVER["HTTP_X_FORWARDED_FOR"])[0]);
+	$forwarded_for = $_SERVER["HTTP_X_FORWARDED_FOR"] ?? $_SERVER["REMOTE_ADDR"] ?? "";
+	$ip=trim(explode(",",$forwarded_for)[0]);
 	$date=date('Y-m-d H:i:s');
 	$last_login_msg=$date." from ".$ip;
 	$sql="UPDATE users SET last_login = ? WHERE id = ?";
@@ -75,7 +77,7 @@ else if ($_SESSION["needs_auth"]===false && $_SESSION["mfa_authenticated"]==1 &&
 	mysqli_stmt_close($stmt);
 	//send login message
 	if($_SESSION["login_message"] && $_SESSION["logged_in"]!==true){
-		$device = $_SERVER['HTTP_USER_AGENT'];
+		$device = $_SERVER['HTTP_USER_AGENT'] ?? "";
 		$location=get_location_from_ip($ip);
 		$message = "⚠️ *Login Warning*\n\n"
 		    . "We noticed a login attempt with your account.\n\n"
diff --git a/app-code/api/login/send_reset_link.php b/app-code/api/login/send_reset_link.php
index 2f86735..746627d 100644
--- a/app-code/api/login/send_reset_link.php
+++ b/app-code/api/login/send_reset_link.php
@@ -1,9 +1,15 @@
 <?php
-session_start();
+include "../utils/security.php";
+secure_session_start();
+require_same_origin_request();
 header('Content-Type: application/json');
 include "../../config/config.php";
 include "../utils/get_location.php";
-$username=$_SESSION["username"];
+$username=$_SESSION["username"] ?? "";
+if ($username === "") {
+	echo json_encode(['success' => false, 'message' => 'Missing username.']);
+	exit;
+}
 $sql="SELECT id, email, telegram_id FROM users WHERE username = ?;";
 $conn = new mysqli($DB_SERVERNAME, $DB_USERNAME, $DB_PASSWORD, $DB_DATABASE);
 $mail="";
@@ -15,11 +21,17 @@ mysqli_stmt_execute($stmt);
 mysqli_stmt_store_result($stmt);
 mysqli_stmt_bind_result($stmt,$id, $mail,$telegram_id);
 mysqli_stmt_fetch($stmt);
+$user_found = mysqli_stmt_num_rows($stmt) === 1;
 mysqli_stmt_close($stmt);
+if (!$user_found) {
+	echo json_encode(['success' => true, 'message' => 'If the account has reset methods configured, a reset link has been sent.']);
+	exit;
+}
 //send telegram message
-$device = $_SERVER['HTTP_USER_AGENT'];
+$device = $_SERVER['HTTP_USER_AGENT'] ?? "";
 //$ip=$_SERVER["REMOTE_ADDR"];
-$ip=trim(explode(",",$_SERVER["HTTP_X_FORWARDED_FOR"])[0]);
+$forwarded_for = $_SERVER["HTTP_X_FORWARDED_FOR"] ?? $_SERVER["REMOTE_ADDR"] ?? "";
+$ip=trim(explode(",",$forwarded_for)[0]);
 $location=get_location_from_ip($ip);
 $date=date('Y-m-d H:i:s');
 $token=bin2hex(random_bytes(128));
@@ -628,11 +640,12 @@ if(!empty($mail)){
 
 
 //insert the token into our db
-$valid_until=time()+(8600/2);
+$valid_until=time()+(12 * 60 * 60);
 $sql="INSERT INTO reset_tokens (auth_token, user_id,valid_until) VALUES (?,?,?);";
 $stmt = mysqli_prepare($conn, $sql);
 mysqli_stmt_bind_param($stmt, 'sii', $token,$id,$valid_until);
 mysqli_stmt_execute($stmt);
 mysqli_stmt_close($stmt);
 
+echo json_encode(['success' => true, 'message' => 'If the account has reset methods configured, a reset link has been sent.']);
 ?>
diff --git a/app-code/api/login/set_username.php b/app-code/api/login/set_username.php
index 8db9a80..c3dcffa 100644
--- a/app-code/api/login/set_username.php
+++ b/app-code/api/login/set_username.php
@@ -1,6 +1,10 @@
 <?php
-session_start();
+include "../utils/security.php";
+secure_session_start();
+require_same_origin_request();
 $_SESSION["needs_auth"]=true;
 $_SESSION["logged_in"]=false;
-$_SESSION["username"]=preg_replace("/[^a-z0-9_]/","",$_POST["username"]);
+$username = strtolower((string) ($_POST["username"] ?? ""));
+$_SESSION["username"]=preg_replace("/[^a-z0-9_]/","",$username);
+session_regenerate_id(true);
 ?>
diff --git a/app-code/api/manage/delete_user.php b/app-code/api/manage/delete_user.php
index d918349..907aa84 100644
--- a/app-code/api/manage/delete_user.php
+++ b/app-code/api/manage/delete_user.php
@@ -1,8 +1,10 @@
 <?php
 header('Content-Type: application/json');
-session_start();
+include "../utils/security.php";
+secure_session_start();
+require_same_origin_request();
 //check for permisisons
-if (!isset($_SESSION["logged_in"]) || $_SESSION["logged_in"] !== true || $_SESSION["permissions"][0]!=="1" ) {
+if (!isset($_SESSION["logged_in"]) || $_SESSION["logged_in"] !== true || !is_admin_session() ) {
     echo(json_encode(['success' => false, 'message'=>'not authenticated']));
         exit();
 }
diff --git a/app-code/api/manage/fetch_users.php b/app-code/api/manage/fetch_users.php
index 75beec0..9376904 100644
--- a/app-code/api/manage/fetch_users.php
+++ b/app-code/api/manage/fetch_users.php
@@ -1,8 +1,9 @@
 <?php
 header('Content-Type: application/json');
-session_start();
+include "../utils/security.php";
+secure_session_start();
 //check for permisisons
-if (!isset($_SESSION["logged_in"]) || $_SESSION["logged_in"] !== true || $_SESSION["permissions"][0]!=="1" ) {
+if (!isset($_SESSION["logged_in"]) || $_SESSION["logged_in"] !== true || !is_admin_session() ) {
     echo(json_encode(['success' => false, 'message'=>'not authenticated']));
     exit();
 }
diff --git a/app-code/api/register/register_user.php b/app-code/api/register/register_user.php
index 5334e98..b6d073c 100644
--- a/app-code/api/register/register_user.php
+++ b/app-code/api/register/register_user.php
@@ -1,5 +1,8 @@
 <?php
 // Set response headers to return JSON
+include "../utils/security.php";
+secure_session_start();
+require_same_origin_request();
 header('Content-Type: application/json');
 
 include "../../config/config.php";
@@ -22,7 +25,7 @@ if ($_SERVER['REQUEST_METHOD'] === 'POST') {
     $data = json_decode($input, true);
 
     // Validate input
-    if (!isset($data['username']) ||  !isset($data['password'])) {
+    if (!is_array($data) || !isset($data['username']) || !isset($data['password'])) {
         echo json_encode([
             'success' => false,
             'message' => 'Invalid input. Username and password are required.'
@@ -30,10 +33,11 @@ if ($_SERVER['REQUEST_METHOD'] === 'POST') {
         exit;
     }
 
-    $username = trim($data['username']);
-    $email = trim($data['email']);
-    $password = trim($data['password']);
-    $telegram_id = trim($data['telegram']);
+    $username = strtolower(trim((string) $data['username']));
+    $username = preg_replace("/[^a-z0-9_]/", "", $username);
+    $email = trim((string) ($data['email'] ?? ""));
+    $password = (string) $data['password'];
+    $telegram_id = trim((string) ($data['telegram'] ?? ""));
 
     // Check for empty fields
     if (empty($username) || empty($password)) {
@@ -44,6 +48,22 @@ if ($_SERVER['REQUEST_METHOD'] === 'POST') {
         exit;
     }
 
+    if (strlen($password) < 12) {
+        echo json_encode([
+            'success' => false,
+            'message' => 'Password must be at least 12 characters.'
+        ]);
+        exit;
+    }
+
+    if ($email !== "" && !filter_var($email, FILTER_VALIDATE_EMAIL)) {
+        echo json_encode([
+            'success' => false,
+            'message' => 'Invalid email address.'
+        ]);
+        exit;
+    }
+
     // Check if the username already exists
     $sql = "SELECT id FROM users WHERE username = ?";
     $stmt = mysqli_prepare($conn, $sql);
diff --git a/app-code/api/utils/check_keepmeloggedin.php b/app-code/api/utils/check_keepmeloggedin.php
index 8e60d54..1347b27 100644
--- a/app-code/api/utils/check_keepmeloggedin.php
+++ b/app-code/api/utils/check_keepmeloggedin.php
@@ -5,17 +5,22 @@
 		$conn = new mysqli($DB_SERVERNAME, $DB_USERNAME, $DB_PASSWORD, $DB_DATABASE);
 		if (isset($_COOKIE['auth_token'])) {
 			$auth_token=$_COOKIE['auth_token'];
+			$auth_token_hash=remember_token_hash($auth_token);
 		    	$sql="SELECT user_id,agent FROM keepmeloggedin WHERE auth_token = ?";
 		    	$user_id=0;
 		    	$agent="";
 			$stmt = mysqli_prepare($conn, $sql);
-			mysqli_stmt_bind_param($stmt, 's',$auth_token);
+			mysqli_stmt_bind_param($stmt, 's',$auth_token_hash);
 			mysqli_stmt_execute($stmt);
 			mysqli_stmt_store_result($stmt);
 			if(mysqli_stmt_num_rows($stmt) == 1){
 				mysqli_stmt_bind_result($stmt, $user_id,$agent);
 				mysqli_stmt_fetch($stmt);
 				mysqli_stmt_close($stmt);
+				if (!hash_equals($agent, $_SERVER['HTTP_USER_AGENT'] ?? "")) {
+					delete_cookie("auth_token");
+					return $ret;
+				}
 				
 				//load user data
 				$sql="SELECT auth_method_required_pw, auth_method_required_2fa, auth_method_required_passkey, username, user_token,last_login, login_message,telegram_id, permissions FROM users WHERE id = ?";
@@ -52,6 +57,7 @@
 					$_SESSION["keepmeloggedin_asked"]=true;
 					$_SESSION["logged_in"]=true;
 					$_SESSION["needs_auth"]=false;
+					session_regenerate_id(true);
 					$ret="success";
 				}
 				mysqli_stmt_close($stmt);
diff --git a/app-code/api/utils/security.php b/app-code/api/utils/security.php
new file mode 100644
index 0000000..d98a5ad
--- /dev/null
+++ b/app-code/api/utils/security.php
@@ -0,0 +1,128 @@
+<?php
+
+function secure_session_start(): void
+{
+    if (session_status() === PHP_SESSION_ACTIVE) {
+        return;
+    }
+
+    $is_https = (!empty($_SERVER['HTTPS']) && $_SERVER['HTTPS'] !== 'off')
+        || (isset($_SERVER['SERVER_PORT']) && (int) $_SERVER['SERVER_PORT'] === 443);
+
+    session_set_cookie_params([
+        'lifetime' => 0,
+        'path' => '/',
+        'domain' => '',
+        'secure' => $is_https,
+        'httponly' => true,
+        'samesite' => 'Lax',
+    ]);
+
+    session_start();
+}
+
+function json_response(array $data, int $status_code = 200): void
+{
+    http_response_code($status_code);
+    header('Content-Type: application/json');
+    echo json_encode($data);
+    exit;
+}
+
+function require_same_origin_request(): void
+{
+    if (!in_array($_SERVER['REQUEST_METHOD'] ?? 'GET', ['POST', 'PUT', 'PATCH', 'DELETE'], true)) {
+        return;
+    }
+
+    $host = $_SERVER['HTTP_HOST'] ?? '';
+    $source = $_SERVER['HTTP_ORIGIN'] ?? $_SERVER['HTTP_REFERER'] ?? '';
+
+    if ($source === '') {
+        return;
+    }
+
+    $source_host = parse_url($source, PHP_URL_HOST);
+    $source_port = parse_url($source, PHP_URL_PORT);
+    if ($source_host && $source_port) {
+        $source_host .= ':' . $source_port;
+    }
+
+    if (!$source_host || !hash_equals(strtolower($host), strtolower($source_host))) {
+        json_response(['success' => false, 'message' => 'Invalid request origin.'], 403);
+    }
+}
+
+function require_logged_in(): void
+{
+    if (!isset($_SESSION['logged_in']) || $_SESSION['logged_in'] !== true || empty($_SESSION['id'])) {
+        json_response(['success' => false, 'message' => 'Not logged in'], 401);
+    }
+}
+
+function is_admin_session(): bool
+{
+    return !empty($_SESSION['permissions'])
+        && is_string($_SESSION['permissions'])
+        && isset($_SESSION['permissions'][0])
+        && $_SESSION['permissions'][0] === '1';
+}
+
+function remember_token_hash(string $token): string
+{
+    return hash('sha256', $token);
+}
+
+function set_secure_cookie(string $name, string $value, int $expires): void
+{
+    $is_https = (!empty($_SERVER['HTTPS']) && $_SERVER['HTTPS'] !== 'off')
+        || (isset($_SERVER['SERVER_PORT']) && (int) $_SERVER['SERVER_PORT'] === 443);
+
+    setcookie($name, $value, [
+        'expires' => $expires,
+        'path' => '/',
+        'secure' => $is_https,
+        'httponly' => true,
+        'samesite' => 'Lax',
+    ]);
+}
+
+function delete_cookie(string $name): void
+{
+    set_secure_cookie($name, '', time() - 3600);
+}
+
+function normalize_redirect_target(?string $target): string
+{
+    $target = trim((string) $target);
+    if ($target === '') {
+        return '/account/';
+    }
+
+    if (preg_match('/[\r\n]/', $target)) {
+        return '/account/';
+    }
+
+    if (str_starts_with($target, '/') && !str_starts_with($target, '//')) {
+        return $target;
+    }
+
+    $parts = parse_url($target);
+    if (!$parts || empty($parts['scheme']) || empty($parts['host'])) {
+        return '/account/';
+    }
+
+    if (!in_array(strtolower($parts['scheme']), ['http', 'https'], true)) {
+        return '/account/';
+    }
+
+    return $target;
+}
+
+function append_auth_token_to_redirect(string $redirect, string $auth_token): string
+{
+    $separator = str_contains($redirect, '?') ? '&' : '?';
+    return $redirect . $separator . 'auth=' . rawurlencode($auth_token);
+}
+
+?>
diff --git a/app-code/index.php b/app-code/index.php
index 522c3cd..d2f3118 100644
--- a/app-code/index.php
+++ b/app-code/index.php
@@ -1,3 +1,20 @@
+<?php
+include "api/utils/security.php";
+include "api/utils/check_keepmeloggedin.php";
+secure_session_start();
+$_SESSION["end_url"]=normalize_redirect_target($_GET["send_to"] ?? "/account/");
+if (isset($_SESSION["logged_in"]) && $_SESSION["logged_in"] === true && !isset($_GET["donotsend"]) /*also check for keepmeloggedin here*/) {
+    header("LOCATION:/login/account_selector.php");
+    exit();
+}
+if(isset($_GET["donotsend"])){
+    delete_cookie("auth_token");
+}
+if(logmein()==="success"){
+    header("LOCATION:/login/account_selector.php");
+    exit();
+}
+?>
 <!DOCTYPE html>
 <html lang="en" data-bs-theme="dark">
 <head>
@@ -8,20 +25,6 @@
   <title>Jakach Login</title>
   <?php
 	include "assets/components.php";
-	include "api/utils/check_keepmeloggedin.php";
-	session_start();
-	$_SESSION["end_url"]=$_GET["send_to"];
-	if (isset($_SESSION["logged_in"]) && $_SESSION["logged_in"] === true && !isset($_GET["donotsend"]) /*also check for keepmeloggedin here*/) {
-	    header("LOCATION:/login/account_selector.php");
-	    exit();
-	}
-	if(isset($_GET["donotsend"])){
-		setcookie("auth_token", "", time() - 3600, "/");
-	}
-	if(logmein()==="success"){
-		header("LOCATION:/login/account_selector.php");
-	    	exit();
-	}
   ?>
 </head>
 <body>
@@ -135,4 +138,3 @@
 ?>
 </body>
 </html>
-
diff --git a/app-code/login/account_selector.php b/app-code/login/account_selector.php
index e4442d0..4866155 100644
--- a/app-code/login/account_selector.php
+++ b/app-code/login/account_selector.php
@@ -1,3 +1,7 @@
+<?php
+include "../api/utils/security.php";
+secure_session_start();
+?>
 <!DOCTYPE html>
 <html lang="en" data-bs-theme="dark">
 <head>
@@ -6,7 +10,6 @@
   <title>Jakach Login</title>
   <?php
 	include "../assets/components.php";
-	session_start();
   ?>
 </head>
 <body>
@@ -22,8 +25,8 @@
               <!-- Submit Button -->
 		<div class="d-grid gap-2">
 		  <!-- Login Button -->
-		  <a href="/login/" class="btn btn-primary btn-lg" id="continueLink">Continue as <?php echo($_SESSION["username"]); ?></a>
-		  <a class="btn btn-outline-primary btn-lg" href="/?donotsend&send_to=<?php echo($_SESSION["end_url"]); ?>">Use another account</a>
+		  <a href="/login/" class="btn btn-primary btn-lg" id="continueLink">Continue as <?php echo(htmlspecialchars($_SESSION["username"] ?? "", ENT_QUOTES, "UTF-8")); ?></a>
+		  <a class="btn btn-outline-primary btn-lg" href="/?donotsend&send_to=<?php echo(rawurlencode($_SESSION["end_url"] ?? "/account/")); ?>">Use another account</a>
 		</div>
             </form>
           </div>
@@ -43,4 +46,3 @@ document.addEventListener("keydown", function(event) {
 </script>
 </body>
 </html>
-
diff --git a/app-code/login/keepmeloggedin.php b/app-code/login/keepmeloggedin.php
index 3d8bbbd..a74e4b1 100644
--- a/app-code/login/keepmeloggedin.php
+++ b/app-code/login/keepmeloggedin.php
@@ -1,3 +1,7 @@
+<?php
+include "../api/utils/security.php";
+secure_session_start();
+?>
 <!DOCTYPE html>
 <html lang="en" data-bs-theme="dark">
 <head>
@@ -6,7 +10,6 @@
   <title>Jakach Login</title>
   <?php
 	include "../assets/components.php";
-	session_start();
   ?>
 </head>
 <body>
@@ -66,4 +69,3 @@
 </script>
 </body>
 </html>
-
diff --git a/app-code/login/logout.php b/app-code/login/logout.php
index a3efd04..d606bd7 100644
--- a/app-code/login/logout.php
+++ b/app-code/login/logout.php
@@ -1,7 +1,8 @@
 <?php
-	session_start();
+	include "../api/utils/security.php";
+	secure_session_start();
 	session_unset();
 	session_destroy();
-	setcookie("auth_token", "", time() - 3600, "/");
+	delete_cookie("auth_token");
 	header("LOCATION:/");
 ?>
diff --git a/app-code/login/mfa.php b/app-code/login/mfa.php
index f23b3b8..9773f35 100644
--- a/app-code/login/mfa.php
+++ b/app-code/login/mfa.php
@@ -1,3 +1,7 @@
+<?php
+include "../api/utils/security.php";
+secure_session_start();
+?>
 <!DOCTYPE html>
 <html lang="en" data-bs-theme="dark">
 <head>
@@ -6,7 +10,6 @@
   <title>Jakach Login</title>
   <?php
 	include "../assets/components.php";
-	session_start();
   ?>
 </head>
 <body>
@@ -112,4 +115,3 @@
 </script>
 </body>
 </html>
-
diff --git a/app-code/login/passkey.php b/app-code/login/passkey.php
index d49c7ad..2d25e6a 100644
--- a/app-code/login/passkey.php
+++ b/app-code/login/passkey.php
@@ -1,3 +1,7 @@
+<?php
+include "../api/utils/security.php";
+secure_session_start();
+?>
 <!DOCTYPE html>
 <html lang="en" data-bs-theme="dark">
 <head>
@@ -6,7 +10,6 @@
   <title>Jakach Login</title>
   <?php
 	include "../assets/components.php";
-	session_start();
   ?>
 </head>
 <body>
@@ -256,4 +259,3 @@ async function checkRegistration() {
 </script>
 </body>
 </html>
-
diff --git a/app-code/login/pw.php b/app-code/login/pw.php
index 6ba6f83..0e63bd5 100644
--- a/app-code/login/pw.php
+++ b/app-code/login/pw.php
@@ -1,3 +1,7 @@
+<?php
+include "../api/utils/security.php";
+secure_session_start();
+?>
 <!DOCTYPE html>
 <html lang="en" data-bs-theme="dark">
 <head>
@@ -6,7 +10,6 @@
   <title>Jakach Login</title>
   <?php
 	include "../assets/components.php";
-	session_start();
   ?>
 </head>
 <body>
@@ -142,4 +145,3 @@
 </script>
 </body>
 </html>
-
diff --git a/app-code/plugins/auth.php b/app-code/plugins/auth.php
index d550bae..a082e7d 100644
--- a/app-code/plugins/auth.php
+++ b/app-code/plugins/auth.php
@@ -2,10 +2,16 @@
 /*
 This file can be installed in any service. If done so a user can authenticate with Jakach Auth. Jakach Auth will redirect the user here where their token gets validated, and then they can be logged in to your service.
 */
-$auth_token = $_GET["auth"];
+$auth_token = $_GET["auth"] ?? "";
+header('Content-Type: application/json');
+
+if ($auth_token === '') {
+    echo json_encode(['status' => 'failure', 'msg' => 'Missing auth token']);
+    exit;
+}
 
 // Check the auth token against Jakach login API
-$check_url = "https://auth.jakach.ch/api/auth/check_auth_key.php?auth_token=" . $auth_token;
+$check_url = "https://auth.jakach.ch/api/auth/check_auth_key.php?auth_token=" . rawurlencode($auth_token);
 
 // Initialize cURL
 $ch = curl_init();
@@ -47,4 +53,3 @@ if (isset($data['status'])) {
     echo json_encode(['status' => 'failure', 'msg' => 'Invalid response from authentication server']);
 }
 ?>
-
diff --git a/app-code/register/index.php b/app-code/register/index.php
index dd47f39..2ad6960 100644
--- a/app-code/register/index.php
+++ b/app-code/register/index.php
@@ -1,5 +1,6 @@
 <?php
-session_start();
+include "../api/utils/security.php";
+secure_session_start();
 ?>
 <!DOCTYPE html>
 <html lang="en" data-bs-theme="dark">
@@ -134,12 +135,8 @@ session_start();
             showModalMessage('Success', 'Registration successful!');
             // Redirect to a different page if needed after closing the modal
             setTimeout(() => {
-              <?php
-              	if(empty($_SESSION["end_url"]))
-              		echo("window.location.href = '/?send_to=/account/';");
-              	else
-              		echo("window.location.href = '/?send_to=".$_SESSION["end_url"]."';");
-              ?>
+              const endUrl = <?php echo json_encode($_SESSION["end_url"] ?? "/account/"); ?>;
+              window.location.href = '/?send_to=' + encodeURIComponent(endUrl);
             }, 2000);
           } else {
             showModalMessage('Error', result.message || 'Registration failed!');