dangerous extension error

app/controllers/api/attachments_controller.rb

@@ -34,6 +34,8 @@ module Api
       end
 
       render json: attachment.as_json(only: %i[uuid created_at], methods: %i[url filename content_type])
+    rescue Submitters::MaliciousFileExtension => e
+      render json: { error: e.message }, status: :unprocessable_entity
     end
 
     def build_new_cookie_signatures_json(submitter, attachment)

app/javascript/submission_form/dropzone.vue

@@ -163,12 +163,20 @@ export default {
             return fetch(this.baseUrl + '/api/attachments', {
               method: 'POST',
               body: formData
-            }).then(resp => resp.json()).then((data) => {
-              return data
+            }).then(async (resp) => {
+              const data = await resp.json()
+
+              if (resp.status === 422) {
+                alert(data.error)
+              } else {
+                return data
+              }
             })
           }
         })).then((result) => {
-        this.$emit('upload', result)
+        if (result && result[0]) {
+          this.$emit('upload', result)
+        }
       }).finally(() => {
         this.isLoading = false
       })

lib/submitters.rb

@@ -13,6 +13,17 @@ module Submitters
 
   UnableToSendCode = Class.new(StandardError)
   InvalidOtp = Class.new(StandardError)
+  MaliciousFileExtension = Class.new(StandardError)
+
+  DANGEROUS_EXTENSIONS = Set.new(%w[
+    exe com bat cmd scr pif vbs vbe js jse wsf wsh msi msp
+    hta cpl jar app deb rpm dmg pkg mpkg dll so dylib sys
+    inf reg ps1 psm1 psd1 ps1xml psc1 pssc bat cmd vb vba
+    sh bash zsh fish run out bin elf gadget workflow lnk scf
+    url desktop application action workflow apk ipa xap appx
+    appxbundle msix msixbundle diagcab diagpkg cpl msc ocx
+    drv scr ins isp mst paf prf shb shs slk ws wsc inf1 inf2
+  ].freeze)
 
   module_function
 
@@ -111,6 +122,12 @@ module Submitters
   def create_attachment!(submitter, params)
     blob =
       if (file = params[:file])
+        extension = File.extname(file.original_filename).delete_prefix('.').downcase
+
+        if DANGEROUS_EXTENSIONS.include?(extension)
+          raise MaliciousFileExtension, "File type '.#{extension}' is not allowed."
+        end
+
         ActiveStorage::Blob.create_and_upload!(io: file.open,
                                                filename: file.original_filename,
                                                content_type: file.content_type)