diff --git a/app/controllers/seminars_controller.rb b/app/controllers/seminars_controller.rb
index dc35ed0..8f80aee 100644
--- a/app/controllers/seminars_controller.rb
+++ b/app/controllers/seminars_controller.rb
@@ -550,6 +550,10 @@ class SeminarsController < ApplicationController
     if flag
       update_params['seminar_submission_values']['0']['value']['en'] = ' '
     end
+    if session[:seminar_signup_id].blank?
+      redirect_to "#{params[:referer_url].to_s.chomp('/')}/?method=con_upload" and return
+    end
+    update_params['seminar_signup_id'] = session[:seminar_signup_id].to_s
     @con = SeminarSignupContribute.new(update_params)
     if @con.save
       signup = SeminarSignup.where(id:update_params['seminar_signup_id']).first
@@ -573,13 +577,17 @@ class SeminarsController < ApplicationController
       @seminar.save
       redirect_to "#{params[:referer_url].to_s.chomp('/')}/?method=con_upload"
     else
-      redirect_to "#{params[:referer_url]}", :notice => t('recaptcha.errors.verification_failed')
+      msg = @con.errors[:file].present? ? t('recaptcha.errors.file_type_not_allowed') : t('recaptcha.errors.verification_failed')
+      redirect_to "#{params[:referer_url].to_s.chomp('/')}/?method=con_upload&notice=#{msg}", :notice => msg
     end
 
   end
 
   def update
     @con = SeminarSignupContribute.find(params[:seminar_signup_contribute][:id])
+    if session[:seminar_signup_id].blank? || @con.seminar_signup_id.to_s != session[:seminar_signup_id].to_s
+      redirect_to "#{params[:referer_url].to_s.chomp('/')}/?method=con_upload" and return
+    end
     update_params = seminar_signup_contribute_params.merge('seminar_submission_values'=>params['seminar_submission_values'].to_h)
     update_params.permit!
     if update_params['seminar_submission_values'].present?
@@ -627,7 +635,8 @@ class SeminarsController < ApplicationController
       @seminar.save
       redirect_to "#{params[:referer_url].to_s.chomp('/')}/?method=con_upload"
     else
-      redirect_to "#{params[:referer_url]}", :notice => t('recaptcha.errors.verification_failed')
+      msg = @con.errors[:file].present? ? t('recaptcha.errors.file_type_not_allowed') : t('recaptcha.errors.verification_failed')
+      redirect_to "#{params[:referer_url].to_s.chomp('/')}/?method=con_upload&notice=#{msg}", :notice => msg
     end
 
   end
@@ -636,6 +645,10 @@ class SeminarsController < ApplicationController
 
     con = SeminarSignupContribute.find(params[:con_no])
 
+    if session[:seminar_signup_id].blank? || con.seminar_signup_id.to_s != session[:seminar_signup_id].to_s
+      redirect_to "#{params[:referer_url].to_s.chomp('/')}/?method=con_upload" and return
+    end
+
     # seminar_signup = SeminarSignup.find_by(_id: con.seminar_signup_id )
     # seminar = SeminarMain.find_by(_id: seminar_signup.seminar_main_id )
     signup = con.seminar_signup
diff --git a/app/models/seminar_signup_contribute.rb b/app/models/seminar_signup_contribute.rb
index 0942997..e6e55e2 100644
--- a/app/models/seminar_signup_contribute.rb
+++ b/app/models/seminar_signup_contribute.rb
@@ -7,7 +7,7 @@ class SeminarSignupContribute
   field :abstract_number , type: String , default: ""
   field :presentation_type , type: String , default: ""
   field :sort_number , type: Integer, default: 10000
-  mount_uploader :file, AssetUploader
+  mount_uploader :file, SeminarContributeUploader 
   field :filename, type: String
   field :description
   field :preferred_session
@@ -62,4 +62,4 @@ class SeminarSignupContribute
     end
     self.filename
   end
-end
\ No newline at end of file
+end
diff --git a/app/uploaders/seminar_contribute_uploader.rb b/app/uploaders/seminar_contribute_uploader.rb
new file mode 100644
index 0000000..22b8065
--- /dev/null
+++ b/app/uploaders/seminar_contribute_uploader.rb
@@ -0,0 +1,14 @@
+# encoding: utf-8
+
+# 研討會投稿是「外部訪客」上傳，與後台可信上傳不同。
+# 繼承核心 AssetUploader（沿用 store_dir、檔名截短），僅加上危險副檔名黑名單，
+# 擋掉會在瀏覽器執行腳本、或可能被伺服器端執行的類型，防止 XSS。
+class SeminarContributeUploader < AssetUploader
+  def extension_blacklist
+    %w[
+      html htm xhtml shtml mhtml svg xml js mjs
+      php php3 php4 php5 phtml pht cgi pl py rb asp aspx jsp jspx sh bash
+      htaccess swf jar hta vbs
+    ]
+  end
+end
diff --git a/app/views/seminars/_contribute_form.html.erb b/app/views/seminars/_contribute_form.html.erb
index 83294ce..01007cf 100644
--- a/app/views/seminars/_contribute_form.html.erb
+++ b/app/views/seminars/_contribute_form.html.erb
@@ -94,7 +94,6 @@
       <input type="hidden" name="referer_url" value="<%= request.original_url.split(request.env["HTTP_HOST"]).last.split('?').first %>">
       <input type="hidden" name="seminar_signup_contribute[seminar_signup_id]" value="<%= session[:seminar_signup_id] %>">
       <%= f.submit "Submit", class: 'btn btn-primary', :id => 'button-mail' %>
-      <%= f.button "Delete", type: 'reset', class: 'btn' %>
     </div>
   </div>
 </fieldset>
@@ -136,4 +135,4 @@
     float: left;
     cursor: pointer;
   }
-</style>
\ No newline at end of file
+</style>
diff --git a/app/views/seminars/con_upload.html.erb b/app/views/seminars/con_upload.html.erb
index 8b7d1b6..5f6e0d1 100644
--- a/app/views/seminars/con_upload.html.erb
+++ b/app/views/seminars/con_upload.html.erb
@@ -22,6 +22,13 @@
 		prefix_url = OrbitHelper.url_to_show(@seminar.to_param)
 	end
 %>
+<% notice = (params[:notice] rescue nil) %>
+<% if notice.present? %>
+  <%= content_tag :p, notice, :class => ["notice alert alert-error in fade"], :style => "color: red; font-weight: bold;" %>
+  <script type="text/javascript">
+    window.alert("<%= notice %>");
+  </script>
+<% end %>
 <% if (@seminar.contribute_start_date.nil? || @seminar.contribute_start_date <= @time_now) && ( @seminar.contribute_end_date.nil? || @seminar.contribute_end_date+1 >= @time_now ) %>
 	<% begin %>
 	<% if !session[:seminar_signup_id].blank? %>
@@ -109,4 +116,4 @@
 	end%>
 <% else %>
 	<%= t("seminar.out_of_date") %>
-<% end %>
\ No newline at end of file
+<% end %>
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 26c147b..4c340c2 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -23,6 +23,7 @@ en:
   recaptcha:
     errors:
       verification_failed: Verification Failed #驗證碼錯誤
+      file_type_not_allowed: This file type is not allowed
   helpers:
     label:
       seminar_review_result:
@@ -214,4 +215,4 @@ en:
     select: Select box
     checkbox: Multiple choice
     radio: Single choice
-    choices: Choices
\ No newline at end of file
+    choices: Choices
diff --git a/config/locales/zh_tw.yml b/config/locales/zh_tw.yml
index 72ddba8..5849f6c 100644
--- a/config/locales/zh_tw.yml
+++ b/config/locales/zh_tw.yml
@@ -23,6 +23,7 @@ zh_tw:
   recaptcha:
     errors:
       verification_failed: 驗證碼錯誤
+      file_type_not_allowed: 檔案格式不允許上傳
   helpers:
     label:
       seminar_review_result:
@@ -214,4 +215,4 @@ zh_tw:
     select: 下拉選單
     checkbox: 多選
     radio: 單選
-    choices: 選項
\ No newline at end of file
+    choices: 選項