diff --git a/lib/Mojolicious/Controller.pm b/lib/Mojolicious/Controller.pm
index 1b92f5ea69..e385a2477e 100644
--- a/lib/Mojolicious/Controller.pm
+++ b/lib/Mojolicious/Controller.pm
@@ -59,6 +59,10 @@ sub encrypted_cookie {
   my $app     = $self->app;
   my $secret  = $app->secrets->[0];
   my $moniker = $app->moniker;
+
+  Carp::croak 'Your secret passphrase must be changed to set encrypted cookies (see FAQ for more)'
+    if !$ENV{MOJO_ALLOW_INSECURE_SECRET} and (!length $secret or $secret eq $moniker);
+
   return $self->cookie($name, Mojo::Util::encrypt_cookie($value, $secret, $moniker), $options);
 }
 
@@ -242,12 +246,24 @@ sub session {
   my $stash = $self->stash;
   $self->app->sessions->load($self) unless exists $stash->{'mojo.active_session'};
 
-  # Hash
   my $session = $stash->{'mojo.session'} //= {};
+
+  # Require changed secret if session data will be set
+  my $set_operation = !!(@_ > 1 || ref $_[0]);
+  if (!$ENV{MOJO_ALLOW_INSECURE_SECRET} and (keys %$session or $set_operation)) {
+    my $app     = $self->app;
+    my $secret  = $app->secrets->[0];
+    my $moniker = $app->moniker;
+
+    Carp::croak 'Your secret passphrase must be changed to set session data (see FAQ for more)'
+      if !length $secret or $secret eq $moniker;
+  }
+
+  # Hash
   return $session unless @_;
 
   # Get
-  return $session->{$_[0]} unless @_ > 1 || ref $_[0];
+  return $session->{$_[0]} unless $set_operation;
 
   # Set
   my $values = ref $_[0] ? $_[0] : {@_};
@@ -262,8 +278,15 @@ sub signed_cookie {
   # Request cookie
   return $self->every_signed_cookie($name)->[-1] unless defined $value;
 
+  my $app     = $self->app;
+  my $secret  = $app->secrets->[0];
+  my $moniker = $app->moniker;
+
+  Carp::croak 'Your secret passphrase must be changed to set signed cookies (see FAQ for more)'
+    if !$ENV{MOJO_ALLOW_INSECURE_SECRET} and (!length $secret or $secret eq $moniker);
+
   # Response cookie
-  my $sum = Digest::SHA::hmac_sha256_hex("$name=$value", $self->app->secrets->[0]);
+  my $sum = Digest::SHA::hmac_sha256_hex("$name=$value", $secret);
   return $self->cookie($name, "$value--$sum", $options);
 }
 
@@ -443,6 +466,9 @@ the same name, and you want to access more than just the last one, you can use L
 are encrypted with ChaCha20-Poly1305, to prevent tampering, and the ones failing decryption will be automatically
 discarded. Note that this method is B<EXPERIMENTAL> and might change without warning!
 
+The L<application secrets|Mojolicious/secrets> B<MUST> be changed from the default to a secure value to set
+encrypted cookies. This requirement can be bypassed by setting the C<MOJO_ALLOW_INSECURE_SECRET> environment variable.
+
 =head2 every_cookie
 
   my $values = $c->every_cookie('foo');
@@ -745,6 +771,10 @@ Persistent data storage for the next few requests, all session data gets seriali
 Base64 encoded in HMAC-SHA256 signed cookies, to prevent tampering. Note that cookies usually have a C<4096> byte
 (4KiB) limit, depending on browser.
 
+The L<application secrets|Mojolicious/secrets> B<MUST> be changed from the default to a secure value to set
+session data in a signed or encrypted cookie. This requirement can be bypassed by setting the
+C<MOJO_ALLOW_INSECURE_SECRET> environment variable.
+
   # Manipulate session
   $c->session->{foo} = 'bar';
   my $foo = $c->session->{foo};
@@ -770,6 +800,9 @@ same name, and you want to access more than just the last one, you can use L</"e
 cryptographically signed with HMAC-SHA256, to prevent tampering, and the ones failing signature verification will be
 automatically discarded.
 
+The L<application secrets|Mojolicious/secrets> B<MUST> be changed from the default to a secure value to set
+signed cookies. This requirement can be bypassed by setting the C<MOJO_ALLOW_INSECURE_SECRET> environment variable.
+
 =head2 stash
 
   my $hash = $c->stash;
diff --git a/t/mojolicious/app.t b/t/mojolicious/app.t
index eeabc1f31c..a7ed8e4d19 100644
--- a/t/mojolicious/app.t
+++ b/t/mojolicious/app.t
@@ -17,6 +17,7 @@ use Mojo::Date;
 use Mojo::File qw(path);
 use Mojo::Home;
 use Mojo::IOLoop;
+use Mojo::Util qw(generate_secret);
 use Mojolicious;
 use Mojolicious::Controller;
 
@@ -658,6 +659,7 @@ subtest 'Override deployment plugins' => sub {
 };
 
 $t = Test::Mojo->new('MojoliciousTest');
+$t->app->secrets([generate_secret]);
 
 # MojoliciousTestController::Foo::plugin_upper_case
 $t->get_ok('/plugin/upper_case')
diff --git a/t/mojolicious/embedded_lite_app.t b/t/mojolicious/embedded_lite_app.t
index 3451499313..ee5d7aac49 100644
--- a/t/mojolicious/embedded_lite_app.t
+++ b/t/mojolicious/embedded_lite_app.t
@@ -15,6 +15,9 @@ use Test::Mojo;
 
 package TestApp;
 use Mojolicious::Lite;
+use Mojo::Util qw(generate_secret);
+
+app->secrets([generate_secret]);
 
 get '/hello' => sub {
   my $c       = shift;
diff --git a/t/mojolicious/longpolling_lite_app.t b/t/mojolicious/longpolling_lite_app.t
index a05573b0d7..ade04b6a5f 100644
--- a/t/mojolicious/longpolling_lite_app.t
+++ b/t/mojolicious/longpolling_lite_app.t
@@ -5,6 +5,7 @@ BEGIN { $ENV{MOJO_REACTOR} = 'Mojo::Reactor::Poll' }
 use Test::Mojo;
 use Test::More;
 use Mojo::IOLoop;
+use Mojo::Util qw(generate_secret);
 use Mojolicious::Lite;
 
 package MyTestApp::Controller;
@@ -14,6 +15,8 @@ sub DESTROY { shift->stash->{destroyed} = 1 }
 
 package main;
 
+app->secrets([generate_secret]);
+
 app->controller_class('MyTestApp::Controller');
 
 get '/write' => sub {
diff --git a/t/mojolicious/rebased_lite_app.t b/t/mojolicious/rebased_lite_app.t
index 008b7e3535..1bf1240c00 100644
--- a/t/mojolicious/rebased_lite_app.t
+++ b/t/mojolicious/rebased_lite_app.t
@@ -5,8 +5,11 @@ BEGIN { $ENV{MOJO_REACTOR} = 'Mojo::Reactor::Poll' }
 use Test::Mojo;
 use Test::More;
 use Mojo::URL;
+use Mojo::Util qw(generate_secret);
 use Mojolicious::Lite;
 
+app->secrets([generate_secret]);
+
 # Rebase hook
 app->hook(
   before_dispatch => sub {
diff --git a/t/mojolicious/session_lite_app.t b/t/mojolicious/session_lite_app.t
index 5d329b07d2..d3a07cff08 100644
--- a/t/mojolicious/session_lite_app.t
+++ b/t/mojolicious/session_lite_app.t
@@ -91,4 +91,21 @@ subtest 'Rotating secrets' => sub {
   };
 };
 
+subtest 'Insecure secret' => sub {
+  subtest 'Insecure secret (signed cookie)' => sub {
+    $t->reset_session;
+    $t->app->secrets([app->moniker]);
+    $t->app->sessions->encrypted(0);
+    $t->get_ok('/login')->status_is(500);
+  };
+
+  subtest 'Insecure secret (encrypted cookie)' => sub {
+    plan skip_all => 'CryptX required!' unless Mojo::Util->CRYPTX;
+    $t->reset_session;
+    $t->app->secrets([app->moniker]);
+    $t->app->sessions->encrypted(1);
+    $t->get_ok('/login')->status_is(500);
+  };
+};
+
 done_testing();
diff --git a/t/mojolicious/validation_lite_app.t b/t/mojolicious/validation_lite_app.t
index fdf08e489b..27dd679b57 100644
--- a/t/mojolicious/validation_lite_app.t
+++ b/t/mojolicious/validation_lite_app.t
@@ -6,8 +6,11 @@ use Test::Mojo;
 use Test::More;
 use Mojo::Asset::Memory;
 use Mojo::Upload;
+use Mojo::Util qw(generate_secret);
 use Mojolicious::Lite;
 
+app->secrets([generate_secret]);
+
 # Custom check
 app->validator->add_check(two => sub { length $_[2] == 2 ? undef : "e:$_[1]" });