diff --git a/EnvelopeGenerator.Web/Controllers/EnvelopeController.cs b/EnvelopeGenerator.Web/Controllers/EnvelopeController.cs
index 9cfe0335..e9eb97c5 100644
--- a/EnvelopeGenerator.Web/Controllers/EnvelopeController.cs
+++ b/EnvelopeGenerator.Web/Controllers/EnvelopeController.cs
@@ -1,10 +1,9 @@
-
-using EnvelopeGenerator.Application.Contracts;
-using EnvelopeGenerator.Application.Services;
+using EnvelopeGenerator.Application.Services;
 using EnvelopeGenerator.Common;
 using EnvelopeGenerator.Web.Services;
 using Microsoft.AspNetCore.Authorization;
 using Microsoft.AspNetCore.Mvc;
+using System.Text.Encodings.Web;
 
 namespace EnvelopeGenerator.Web.Controllers
 {
@@ -13,13 +12,13 @@ namespace EnvelopeGenerator.Web.Controllers
     {
         private readonly EnvelopeOldService envelopeService;
         private readonly ActionService? actionService;
-        private readonly IEnvelopeService _envelopeService;
+        private readonly UrlEncoder _urlEncoder;
 
-        public EnvelopeController(DatabaseService database, EnvelopeOldService envelope, ILogger<EnvelopeController> logger, IEnvelopeService envService) : base(database, logger)
+        public EnvelopeController(DatabaseService database, EnvelopeOldService envelope, ILogger<EnvelopeController> logger, UrlEncoder urlEncoder) : base(database, logger)
         {
             envelopeService = envelope;
             actionService = database?.Services?.actionService;
-            _envelopeService = envService;
+            _urlEncoder = urlEncoder;
         }
 
         [NonAction]
@@ -28,6 +27,8 @@ namespace EnvelopeGenerator.Web.Controllers
         {
             try
             {
+                envelopeKey = _urlEncoder.Encode(envelopeKey);
+
                 // Validate Envelope Key and load envelope
                 envelopeService.EnsureValidEnvelopeKey(envelopeKey);
             
@@ -52,6 +53,8 @@ namespace EnvelopeGenerator.Web.Controllers
         {
             try
             {
+                envelopeKey = _urlEncoder.Encode(envelopeKey);
+
                 var authSignature = this.GetAuthenticatedReceiverSignature();
 
                 if (authSignature != envelopeKey.GetReceiverSignature())
diff --git a/EnvelopeGenerator.Web/Controllers/HomeController.cs b/EnvelopeGenerator.Web/Controllers/HomeController.cs
index e60699a4..8ad913ed 100644
--- a/EnvelopeGenerator.Web/Controllers/HomeController.cs
+++ b/EnvelopeGenerator.Web/Controllers/HomeController.cs
@@ -16,6 +16,9 @@ using EnvelopeGenerator.Application.DTOs;
 using Microsoft.AspNetCore.Localization;
 using Newtonsoft.Json.Linq;
 using Microsoft.Extensions.Configuration;
+using Ganss.Xss;
+using System.Text.Encodings.Web;
+using EnvelopeGenerator.Domain.Entities;
 
 namespace EnvelopeGenerator.Web.Controllers
 {
@@ -26,22 +29,26 @@ namespace EnvelopeGenerator.Web.Controllers
         private readonly IEnvelopeHistoryService _historyService;
         private readonly IStringLocalizer<Resource> _localizer;
         private readonly IConfiguration _configuration;
+        private readonly UrlEncoder _urlEncoder;
 
-        public HomeController(DatabaseService databaseService, EnvelopeOldService envelopeOldService, ILogger<HomeController> logger, IEnvelopeReceiverService envelopeReceiverService, IEnvelopeHistoryService historyService, IStringLocalizer<Resource> localizer, IConfiguration configuration) : base(databaseService, logger)
+        public HomeController(DatabaseService databaseService, EnvelopeOldService envelopeOldService, ILogger<HomeController> logger, IEnvelopeReceiverService envelopeReceiverService, IEnvelopeHistoryService historyService, IStringLocalizer<Resource> localizer, IConfiguration configuration, UrlEncoder urlEncoder) : base(databaseService, logger)
         {
             this.envelopeOldService = envelopeOldService;
             _envRcvService = envelopeReceiverService;
             _historyService = historyService;
             _localizer = localizer;
             _configuration = configuration;
+            _urlEncoder = urlEncoder;
         }
         
         [HttpGet("/EnvelopeKey/{envelopeReceiverId}")]
         public async Task<IActionResult> SendAccessCode([FromRoute] string envelopeReceiverId)
         {
-            ViewData["EnvelopeKey"] = envelopeReceiverId;
             try
             {
+                envelopeReceiverId = _urlEncoder.Encode(envelopeReceiverId);
+                ViewData["EnvelopeKey"] = envelopeReceiverId;
+
                 return await _envRcvService.ReadByEnvelopeReceiverIdAsync(envelopeReceiverId: envelopeReceiverId).ThenAsync<EnvelopeReceiverDto, IActionResult>(
                     SuccessAsync: async er =>
                     {
@@ -77,6 +84,7 @@ namespace EnvelopeGenerator.Web.Controllers
         {
             try
             {
+                envelopeReceiverId = _urlEncoder.Encode(envelopeReceiverId);
                 ViewData["Languages"] = _configuration.GetSection("Languages").Get<string[]>()!;
                 ViewData["UserLanguage"] = UserLanguage;
 
@@ -100,6 +108,7 @@ namespace EnvelopeGenerator.Web.Controllers
         {
             try
             {
+                envelopeReceiverId = _urlEncoder.Encode(envelopeReceiverId);
                 (string? uuid, string? signature) = envelopeReceiverId.DecodeEnvelopeReceiverId();
 
                 if(uuid is null || signature is null)
@@ -187,6 +196,7 @@ namespace EnvelopeGenerator.Web.Controllers
         {
             try
             {
+                envelopeReceiverId = _urlEncoder.Encode(envelopeReceiverId);
                 return await _envRcvService.IsExisting(envelopeReceiverId: envelopeReceiverId).ThenAsync(
                     SuccessAsync: async isExisting =>
                     {
@@ -231,6 +241,7 @@ namespace EnvelopeGenerator.Web.Controllers
         {
             try
             {
+                language = _urlEncoder.Encode(language);
                 var cookieOptions = new CookieOptions()
                 {
                     Expires = DateTimeOffset.UtcNow.AddYears(1),
diff --git a/EnvelopeGenerator.Web/Controllers/Test/TestSanitizeController.cs b/EnvelopeGenerator.Web/Controllers/Test/TestSanitizeController.cs
new file mode 100644
index 00000000..5ea4e3be
--- /dev/null
+++ b/EnvelopeGenerator.Web/Controllers/Test/TestSanitizeController.cs
@@ -0,0 +1,37 @@
+using Ganss.Xss;
+using Microsoft.AspNetCore.Mvc;
+using System.Text.Encodings.Web;
+
+namespace EnvelopeGenerator.Web.Controllers.Test
+{
+    [ApiController]
+    [Route("api/test/[controller]")]
+    public class TestSanitizeController : ControllerBase
+    {
+        private readonly HtmlEncoder _htmlEncoder;
+        private readonly HtmlSanitizer _sanitizer;
+
+        public TestSanitizeController(HtmlEncoder htmlEncoder, HtmlSanitizer sanitizer)
+        {
+            _htmlEncoder = htmlEncoder;
+            _sanitizer = sanitizer;
+        }
+
+        [HttpGet("sanitize")]
+        public IActionResult Sanitize([FromQuery] string? input = null) => Ok(new
+        {
+            input,
+            Sanitized = _sanitizer.Sanitize(input),
+            SanitizedDocument = _sanitizer.SanitizeDocument(input),
+            SanitizedDom = _sanitizer.SanitizeDom(input)
+        });
+
+
+        [HttpGet("encode")]
+        public IActionResult Encoder([FromQuery] string? input = null) => Ok(new
+        {
+            input,
+            Encoded = _htmlEncoder.Encode(input)
+        });
+    }
+}
diff --git a/EnvelopeGenerator.Web/EnvelopeGenerator.Web.csproj b/EnvelopeGenerator.Web/EnvelopeGenerator.Web.csproj
index e2114c7b..6f4e9152 100644
--- a/EnvelopeGenerator.Web/EnvelopeGenerator.Web.csproj
+++ b/EnvelopeGenerator.Web/EnvelopeGenerator.Web.csproj
@@ -12,6 +12,7 @@
 
   <ItemGroup>
     <PackageReference Include="AutoMapper" Version="13.0.1" />
+    <PackageReference Include="HtmlSanitizer" Version="8.0.865" />
     <PackageReference Include="Microsoft.AspNetCore.OpenApi" Version="7.0.4" />
     <PackageReference Include="Microsoft.EntityFrameworkCore" Version="7.0.16" />
     <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="7.0.15">
diff --git a/EnvelopeGenerator.Web/Program.cs b/EnvelopeGenerator.Web/Program.cs
index c4286df3..52028ab2 100644
--- a/EnvelopeGenerator.Web/Program.cs
+++ b/EnvelopeGenerator.Web/Program.cs
@@ -14,6 +14,8 @@ using Microsoft.AspNetCore.Authentication.Cookies;
 using DigitalData.UserManager.Application.MappingProfiles;
 using EnvelopeGenerator.Web.Models;
 using DigitalData.Core.DTO;
+using System.Text.Encodings.Web;
+using Ganss.Xss;
 
 var logger = LogManager.Setup().LoadConfigurationFromAppSettings().GetCurrentClassLogger();
 logger.Info("Logging initialized!");
@@ -151,6 +153,15 @@ try
 
     builder.Services.AddCookieBasedLocalizer();
 
+    builder.Services.AddSingleton(HtmlEncoder.Default);
+    builder.Services.AddSingleton(UrlEncoder.Default);
+    builder.Services.AddSingleton(_ =>
+    {
+        var sanitizer = new HtmlSanitizer();
+        //configure sanitzer
+        return sanitizer;
+    });
+
     var app = builder.Build();
 
     // Configure the HTTP request pipeline.
@@ -166,6 +177,15 @@ try
 
     app.UseHttpsRedirection();
     app.UseStaticFiles();
+
+    var csp = builder.Configuration["Content-Security-Policy"];
+    if(csp is not null)
+        app.Use(async (context, next) =>
+        {
+            context.Response.Headers.Add("Content-Security-Policy", csp);
+            await next();
+        });
+
     app.UseCookiePolicy();
 
     app.UseRouting();
diff --git a/EnvelopeGenerator.Web/Views/Home/EnvelopeLocked.cshtml b/EnvelopeGenerator.Web/Views/Home/EnvelopeLocked.cshtml
index 8533e09b..02eb5038 100644
--- a/EnvelopeGenerator.Web/Views/Home/EnvelopeLocked.cshtml
+++ b/EnvelopeGenerator.Web/Views/Home/EnvelopeLocked.cshtml
@@ -1,25 +1,8 @@
 @{
     ViewData["Title"] = "Dokument geschützt";
-    string userLanguage = ViewData["UserLanguage"] as string;
-    string[] languages = ViewData["Languages"] as string[];
+    var userLanguage = ViewData["UserLanguage"] as string;
+    var languages = ViewData["Languages"] as string[];
 }
-@* @if(ViewData["UserLanguage"] == null){
-    <script>
-        fetch('/api/data', {  // Assuming the API endpoint is '/api/data' on the same origin
-            method: 'POST',
-            headers: {
-                'Content-Type': 'application/json'
-            },
-            body: JSON.stringify({
-                key: 'value'
-            })
-        })
-        .then(response => response.json())
-        .then(data => console.log(data))
-        .catch(error => console.error('Error:', error));
-    </script>
-} *@
-
 <div class="page container p-5">
     <header class="text-center">
         <div class="icon locked">
@@ -30,18 +13,15 @@
         </div>
         <h1>Dokument erfordert einen Zugriffscode</h1>
     </header>
-
     <section class="text-center">
         <p>Wir haben Ihnen gerade den Zugriffscode an die hinterlegte Email Adresse gesendet. Dies kann evtl. einige Minuten dauern.</p>
     </section>
-
     <section class="d-flex">
         <form id="form-access-code" class="form pl-0 ml-0" method="post">
             <div class="input">
                 <label class="visually-hidden" for="access_code">Zugriffscode</label>
                 <input type="password" id="access_code" class="form-control" name="access_code" placeholder="Zugriffscode" required="required">
             </div>
-
             <div class="button">
                 <button type="submit" class="btn btn-primary">Öffnen</button>
             </div>
@@ -49,15 +29,15 @@
         <form class="form pl-0 ml-0" method="post" action="/lang">
             <div class="dropdown">
                 <select class="form-select" name="language" onchange="this.form.submit()">
-                    @foreach(var lang in languages)
-                    {
-                        <option data-icon="flag-icon flag-icon-us" value="@lang">@_localizer[@lang]</option>
-                    }
+                    @if(languages is not null)
+                        foreach(var lang in languages)
+                        {
+                    <option data-icon="flag-icon flag-icon-us" value="@lang.TrySanitize(_sanitizer)">@_localizer[@lang].Value.TrySanitize(_sanitizer)</option>
+                        }
                 </select>
             </div>
         </form>
     </section>
-
     <section class="text-center">
         <details>
             <summary>Sie haben keinen Zugriffscode erhalten?</summary>
@@ -65,5 +45,4 @@
         </details>
     </section>
 </div>
-
 <footer class="container" id="page-footer">&copy; SignFlow 2023-2024 <a href="https://digitaldata.works">Digital Data GmbH</a></footer>
\ No newline at end of file
diff --git a/EnvelopeGenerator.Web/Views/Home/ShowEnvelope.cshtml b/EnvelopeGenerator.Web/Views/Home/ShowEnvelope.cshtml
index e9df6852..b603db80 100644
--- a/EnvelopeGenerator.Web/Views/Home/ShowEnvelope.cshtml
+++ b/EnvelopeGenerator.Web/Views/Home/ShowEnvelope.cshtml
@@ -18,7 +18,7 @@
         <button class="navbar-toggler" type="button" data-bs-toggle="collapse" data-bs-target="#navbarToggleExternalContent" aria-controls="navbarToggleExternalContent" aria-expanded="false" aria-label="Toggle navigation">
             <span class="navbar-toggler-icon"></span>
         </button>
-            <div class="navbar-brand me-auto ms-5 envelope-message">@($"Hallo {Model.Name}, {@envelope?.Message}")</div>
+            <div class="navbar-brand me-auto ms-5 envelope-message">@($"Hallo {Model.Name.TrySanitize(_sanitizer)}, {@envelope?.Message.TrySanitize(_sanitizer)}")</div>
         <div class="col-1  p-0 m-0 me-3 d-flex">
             <img src="~/img/digital_data.svg" alt="...">
         </div>
@@ -33,9 +33,9 @@
                 </div>
                 <div class="col p-0 m-0">
                     <div class="card-body p-0 m-0">
-                        <h5 class="card-title p-0 m-0">@($"{envelope?.Title}")</h5>
-                        <p class="card-text p-0 m-0">@($"Sie haben {(pages.Count())} Briefe zu unterschreiben. Bitte prüfen Sie die Seiten {stPageIndexes}.")</p>
-                            <p class="card-text p-0 m-0"><small class="text-body-secondary">Erstellt am @envelope?.AddedWhen von @sender?.Prename @sender?.Name. Sie können den Absender über <a href="mailto:@(sender?.Email)?subject=@(envelope?.Title)&body=Sehr%20geehrter%20@(sender?.Prename)%20@(sender?.Name),%0A%0A%0A">@sender?.Email</a> kontaktieren.</small></p>
+                        <h5 class="card-title p-0 m-0">@($"{envelope?.Title.TrySanitize(_sanitizer)}")</h5>
+                        <p class="card-text p-0 m-0">@($"Sie haben {(pages.Count())} Briefe zu unterschreiben. Bitte prüfen Sie die Seiten {stPageIndexes.TrySanitize(_sanitizer)}.")</p>
+                        <p class="card-text p-0 m-0"><small class="text-body-secondary">Erstellt am @envelope?.AddedWhen von @sender?.Prename.TrySanitize(_sanitizer) @sender?.Name.TrySanitize(_sanitizer). Sie können den Absender über <a href="mailto:@(sender?.Email.TryEncode(_encoder))?subject=@(envelope?.Title.TryEncode(_encoder))&body=Sehr%20geehrter%20@(sender?.Prename.TryEncode(_encoder))%20@(sender?.Name.TryEncode(_encoder)),%0A%0A%0A">@sender?.Email.TryEncode(_encoder)</a> kontaktieren.</small></p>
                     </div>
                 </div>
             </div>
@@ -66,8 +66,10 @@
 
     var documentBase64String = Convert.ToBase64String(documentBytes);
 
+    var envelopeKey = ViewData["EnvelopeKey"] as string;
+
     <script>
-        var base64String = "@Html.Raw(documentBase64String)";
+        var base64String = "@Html.Raw(documentBase64String.TrySanitize(_sanitizer))";
         var byteCharacters = atob(base64String);
         var byteNumbers = new Array(byteCharacters.length);
         for (var i = 0; i < byteCharacters.length; i++) {
@@ -76,9 +78,9 @@
         var byteArray = new Uint8Array(byteNumbers);
         var documentArrayBuffer = byteArray.buffer;
 
-        var envelopeResponse = @Html.Raw(envelopeResponseJson);
+        var envelopeResponse = @Html.Raw(envelopeResponseJson.TrySanitize(_sanitizer));
         document.addEventListener("DOMContentLoaded", async () => {
-            const app = new App("#app", "@ViewData["EnvelopeKey"]", envelopeResponse, documentArrayBuffer, "@ViewData["PSPDFKitLicenseKey"]");
+            const app = new App("#app", "@envelopeKey.TrySanitize(_sanitizer)", envelopeResponse, documentArrayBuffer, "@ViewData["PSPDFKitLicenseKey"]");
             await app.init();
         })
     </script>
diff --git a/EnvelopeGenerator.Web/Views/TestView/DebugEnvelopes.cshtml b/EnvelopeGenerator.Web/Views/TestView/DebugEnvelopes.cshtml
index 8c6179fc..ba6773b8 100644
--- a/EnvelopeGenerator.Web/Views/TestView/DebugEnvelopes.cshtml
+++ b/EnvelopeGenerator.Web/Views/TestView/DebugEnvelopes.cshtml
@@ -31,7 +31,7 @@
                         <section>
                             <article class="envelope">
                                 <strong><a href="/EnvelopeKey/@encodeEnvelopeKey(envelope)">@envelope.Title</a></strong>
-                                <div><strong>Ersteller</strong> @envelope.User.Email</div>
+                                <div><strong>Ersteller</strong> @envelope.User.Email.TrySanitize(_sanitizer)</div>
                                 <div><strong>Datum</strong> @envelope.AddedWhen</div>
                             </article>
                         </section>
diff --git a/EnvelopeGenerator.Web/Views/_ViewImports.cshtml b/EnvelopeGenerator.Web/Views/_ViewImports.cshtml
index b74b04e5..131d7f99 100644
--- a/EnvelopeGenerator.Web/Views/_ViewImports.cshtml
+++ b/EnvelopeGenerator.Web/Views/_ViewImports.cshtml
@@ -3,4 +3,6 @@
 @using Microsoft.Extensions.Localization;
 @using EnvelopeGenerator.Application.Resources;
 @inject IStringLocalizer<Resource> _localizer;
+@inject System.Text.Encodings.Web.UrlEncoder _encoder
+@inject Ganss.Xss.HtmlSanitizer _sanitizer
 @addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers
\ No newline at end of file
diff --git a/EnvelopeGenerator.Web/XSSExtensions.cs b/EnvelopeGenerator.Web/XSSExtensions.cs
new file mode 100644
index 00000000..9c019dc2
--- /dev/null
+++ b/EnvelopeGenerator.Web/XSSExtensions.cs
@@ -0,0 +1,12 @@
+using Ganss.Xss;
+using System.Text.Encodings.Web;
+
+namespace EnvelopeGenerator.Web
+{
+    public static class XSSExtensions
+    {
+        public static string? TryEncode(this string? value, UrlEncoder encoder) => value is null ? value : encoder.Encode(value);
+
+        public static string? TrySanitize(this string? html, HtmlSanitizer sanitizer) => html is null ? html : sanitizer.Sanitize(html);
+    }
+}
\ No newline at end of file
diff --git a/EnvelopeGenerator.Web/appsettings.json b/EnvelopeGenerator.Web/appsettings.json
index c0a2b657..2c82090f 100644
--- a/EnvelopeGenerator.Web/appsettings.json
+++ b/EnvelopeGenerator.Web/appsettings.json
@@ -9,6 +9,9 @@
     }
   },
   "PSPDFKitLicenseKey": null,
+  /*  recommended Content-Security-Policy for production:
+      "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'; img-src 'self';"  */
+  "Content-Security-Policy": null,
   "AdminPassword": "dd",
   "AllowedOrigins": [ "https://localhost:7202" ],
   "NLog": {
@@ -57,10 +60,10 @@
 
     ]
   },
-  "AddTestControllers": false,
+  "AddTestControllers": true,
   "Jwt": {
-    "Issuer": "https://localhost:7202",
-    "Audience": "https://localhost:7202",
+    "Issuer": null,
+    "Audience": null,
     "Key": "8RGnd7x0G2TYLOIW4m_qlIls7MfbAIGNrpQJzMAUIvULHOLiG723znRa_MG-Z4yw3SErusOU4hTui2rVBMcCaQ"
   },
   "AuthCookieConfig": {