diff --git a/templates/etc/nginx/sites-available/cryptpad.j2 b/templates/etc/nginx/sites-available/cryptpad.j2
index e55eeb7..589e44f 100644
--- a/templates/etc/nginx/sites-available/cryptpad.j2
+++ b/templates/etc/nginx/sites-available/cryptpad.j2
@@ -13,16 +13,27 @@
   set $main_domain "{{ item.ssl_name }}";
   set $sandbox_domain "sandbox.{{ item.ssl_name }}";
 
+  # By default CryptPad allows remote domains to embed CryptPad documents in iframes.
+  # This behaviour can be blocked by changing $allowed_origins from "*" to the
+  # sandbox domain, which must be permitted to load content from the main domain
+  # in order for CryptPad to work as expected.
+  #
+  # An example is given below which can be uncommented if you want to block
+  # remote sites from including content from your server
+  set $allowed_origins "*";
+  # set $allowed_origins "https://${sandbox_domain}";
+
   # CryptPad's dynamic content (websocket traffic and encrypted blobs)
   # can be served over separate domains. Using dedicated domains (or subdomains)
   # for these purposes allows you to move them to a separate machine at a later date
   # if you find that a single machine cannot handle all of your users.
   # If you don't use dedicated domains, this can be the same as $main_domain
-  # If you do, they'll be added as exceptions to any rules which block connections to remote domains.
+  # If you do, they can be added as exceptions to any rules which block connections to remote domains.
+  # You can find these variables referenced below in the relevant places.
   set $api_domain "{{ item.ssl_name }}";
   set $files_domain "{{ item.ssl_name }}";
 
-  add_header Access-Control-Allow-Origin "*";
+  add_header Access-Control-Allow-Origin "${allowed_origins}";
 
   #set $coop '';
  #if ($uri ~ ^\/(sheet|presentation|doc|convert)\/.*$) { set $coop 'same-origin'; }
@@ -33,7 +44,7 @@
   # Enable SharedArrayBuffer in Firefox (for .xlsx export)
   add_header Cross-Origin-Resource-Policy cross-origin;
   add_header Cross-Origin-Embedder-Policy require-corp;
-    
+
   # any static assets loaded with "ver=" in their URL will be cached for a year
   if ($args ~ ver=) {
     set $cacheControl max-age=31536000;
@@ -48,6 +59,8 @@
   set $styleSrc   "'unsafe-inline' 'self' https://${main_domain}";
 
   # connect-src restricts URLs which can be loaded using script interfaces
+  # if you have configured your instance to use a dedicated $files_domain or $api_domain
+  # you will need to add them below as: https://${files_domain} and https://${api_domain}
   set $connectSrc "'self' https://${main_domain} blob: wss://${api_domain} https://${sandbox_domain}";
 
   # fonts can be loaded from data-URLs or the main domain
@@ -75,6 +88,13 @@
   # script-src specifies valid sources for javascript, including inline handlers
   set $scriptSrc  "'self' resource: https://${main_domain}";
 
+  # frame-ancestors specifies which origins can embed your CryptPad instance
+  # this must include 'self' and your main domain (over HTTPS) in order for CryptPad to work
+  # if you have enabled remote embedding via the admin panel then this must be more permissive.
+  # note: cryptpad.fr permits web pages served via https: and vector: (element desktop app)
+  set $frameAncestors "'self' https://${main_domain}";
+  # set $frameAncestors "'self' https: vector:";
+
   set $unsafe 0;
   # the following assets are loaded via the sandbox domain
   # they unfortunately still require exceptions to the sandboxing to work correctly.
@@ -95,7 +115,7 @@
   }
 
   # Finally, set all the rules you composed above.
-  add_header Content-Security-Policy "default-src 'none'; child-src $childSrc; worker-src $workerSrc; media-src $mediaSrc; style-src $styleSrc; script-src $scriptSrc; connect-src $connectSrc; font-src $fontSrc; img-src $imgSrc; frame-src $frameSrc;";
+  add_header Content-Security-Policy "default-src 'none'; child-src $childSrc; worker-src $workerSrc; media-src $mediaSrc; style-src $styleSrc; script-src $scriptSrc; connect-src $connectSrc; font-src $fontSrc; img-src $imgSrc; frame-src $frameSrc; frame-ancestors $frameAncestors";
 {% endblock %}
 
 {% block root %}
@@ -152,7 +172,7 @@
   # encrypted blobs are immutable and are thus cached for a year
   location ^~ /blob/ {
     if ($request_method = 'OPTIONS') {
-        add_header 'Access-Control-Allow-Origin' '*';
+        add_header 'Access-Control-Allow-Origin' "${allowed_origins}";
         add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
         add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Content-Range,Range';
         add_header 'Access-Control-Max-Age' 1728000;
@@ -160,8 +180,9 @@
         add_header 'Content-Length' 0;
         return 204;
     }
+    add_header X-Content-Type-Options nosniff;
     add_header Cache-Control max-age=31536000;
-    add_header 'Access-Control-Allow-Origin' '*';
+    add_header 'Access-Control-Allow-Origin' "${allowed_origins}";
     add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS';
     add_header 'Access-Control-Allow-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Content-Range,Range,Content-Length';
     add_header 'Access-Control-Expose-Headers' 'DNT,X-CustomHeader,Keep-Alive,User-Agent,X-Requested-With,If-Modified-Since,Cache-Control,Content-Type,Content-Range,Range,Content-Length';
@@ -172,6 +193,7 @@
   # these payloads are unlocked via login credentials. They are mutable
   # and are thus never cached. They're small enough that it doesn't matter, in any case.
   location ^~ /block/ {
+    add_header X-Content-Type-Options nosniff;
     add_header Cache-Control max-age=0;
     try_files $uri =404;
   }