diff --git a/Gemfile b/Gemfile
index 90b4021f6..0f70db5a3 100644
--- a/Gemfile
+++ b/Gemfile
@@ -48,7 +48,7 @@ end
 gem 'mysql2'
 
 # Webserver - included in development and test and optionally in production
-gem 'puma'
+gem 'puma', '>= 6.4.3'
 
 gem 'bootsnap', require: false
 gem 'csv'
diff --git a/Gemfile.lock b/Gemfile.lock
index 6bb903f2a..8c2a326e1 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -592,7 +592,7 @@ DEPENDENCIES
   net-smtp
   oauth2
   pdf-reader
-  puma
+  puma (>= 6.4.3)
   rack-cors
   rails (~> 8.0)
   rails-latex
diff --git a/app/middleware/request_smuggling_protection.rb b/app/middleware/request_smuggling_protection.rb
new file mode 100644
index 000000000..46f4be7f8
--- /dev/null
+++ b/app/middleware/request_smuggling_protection.rb
@@ -0,0 +1,56 @@
+# frozen_string_literal: true
+
+require 'json'
+
+#
+# Rejects ambiguous HTTP framing headers to reduce request smuggling risk.
+#
+class RequestSmugglingProtection
+  BAD_REQUEST_RESPONSE = [
+    400,
+    { 'Content-Type' => 'application/json', 'Connection' => 'close' },
+    [{ error: 'Malformed request framing headers' }.to_json]
+  ].freeze
+
+  def initialize(app)
+    @app = app
+  end
+
+  def call(env)
+    return BAD_REQUEST_RESPONSE if malformed_framing_headers?(env)
+
+    @app.call(env)
+  end
+
+  private
+
+  def malformed_framing_headers?(env)
+    content_length = env['CONTENT_LENGTH']
+    transfer_encoding = env['HTTP_TRANSFER_ENCODING']
+
+    conflicting_content_length_and_transfer_encoding?(content_length, transfer_encoding) ||
+      invalid_content_length?(content_length) ||
+      invalid_transfer_encoding?(transfer_encoding)
+  end
+
+  def conflicting_content_length_and_transfer_encoding?(content_length, transfer_encoding)
+    header_present?(content_length) && header_present?(transfer_encoding)
+  end
+
+  def invalid_content_length?(content_length)
+    return false unless header_present?(content_length)
+
+    content_length.include?(',') || content_length !~ /\A\d+\z/
+  end
+
+  def invalid_transfer_encoding?(transfer_encoding)
+    return false unless header_present?(transfer_encoding)
+
+    normalized = transfer_encoding.split(',').map(&:strip).reject(&:empty?)
+    normalized != ['chunked']
+  end
+
+  def header_present?(value)
+    !value.nil? && !value.strip.empty?
+  end
+end
diff --git a/config/application.rb b/config/application.rb
index fe280a289..f81483010 100644
--- a/config/application.rb
+++ b/config/application.rb
@@ -5,6 +5,8 @@
 require 'csv'
 require 'yaml'
 require 'bunny-pub-sub/services_manager'
+require_relative '../app/middleware/request_smuggling_protection'
+
 
 # Precompile assets before deploying to production
 if defined?(Bundler)
@@ -250,6 +252,7 @@ def self.fetch_boolean_env(name)
         resource '*', headers: :any, methods: %i(get post put delete options)
       end
     end
+    config.middleware.insert_before Rack::Cors, RequestSmugglingProtection
 
     config.active_support.to_time_preserves_timezone = :zone
 
diff --git a/config/puma.rb b/config/puma.rb
index d9b3e836c..e6c509667 100644
--- a/config/puma.rb
+++ b/config/puma.rb
@@ -32,6 +32,22 @@
 #
 # workers ENV.fetch("WEB_CONCURRENCY") { 2 }
 
+workers ENV.fetch("WEB_CONCURRENCY", 2)
+threads_count = ENV.fetch("RAILS_MAX_THREADS", 5)
+threads threads_count, threads_count
+preload_app!
+port        ENV.fetch("PORT", 3000)
+environment ENV.fetch("RAILS_ENV", "development")
+
+# SECURITY FIX: Raise on SIGTERM to prevent request queue poisoning
+raise_exception_on_sigterm
+
+# SECURITY FIX: Reject malformed/early-hint requests
+# Forces Puma 6.x strict HTTP parsing mode
+lowlevel_error_handler do |err, env, status|
+  [400, { "Content-Type" => "text/plain" }, ["Bad Request"]]
+end
+
 # Use the `preload_app!` method when specifying a `workers` number.
 # This directive tells Puma to first boot the application and load code
 # before forking the application. This takes advantage of Copy On Write