fix: Parse Server option fileExtensions default value rejects file extensions that are less than 3 or more than 4 characters long (#8699)

spec/ParseFile.spec.js

@@ -1364,6 +1364,18 @@ describe('Parse.File testing', () => {
       );
     });
 
+    it('default should allow common types', async () => {
+      await reconfigureServer({
+        fileUpload: {
+          enableForPublic: true,
+        },
+      });
+      for (const type of ['plain', 'txt', 'png', 'jpg', 'gif', 'doc']) {
+        const file = new Parse.File(`parse-server-logo.${type}`, { base64: 'ParseA==' });
+        await file.save();
+      }
+    });
+
     it('works with a period in the file name', async () => {
       await reconfigureServer({
         fileUpload: {

src/Options/Definitions.js

@@ -1022,9 +1022,9 @@ module.exports.FileUploadOptions = {
   fileExtensions: {
     env: 'PARSE_SERVER_FILE_UPLOAD_FILE_EXTENSIONS',
     help:
-      "Sets the allowed file extensions for uploading files. The extension is defined as an array of file extensions, or a regex pattern.<br><br>It is recommended to restrict the file upload extensions as much as possible. HTML files are especially problematic as they may be used by an attacker who uploads a HTML form to look legitimate under your app's domain name, or to compromise the session token of another user via accessing the browser's local storage.<br><br>Defaults to `^[^hH][^tT][^mM][^lL]?$` which allows any file extension except HTML files.",
+      "Sets the allowed file extensions for uploading files. The extension is defined as an array of file extensions, or a regex pattern.<br><br>It is recommended to restrict the file upload extensions as much as possible. HTML files are especially problematic as they may be used by an attacker who uploads a HTML form to look legitimate under your app's domain name, or to compromise the session token of another user via accessing the browser's local storage.<br><br>Defaults to `^(?!(h|H)(t|T)(m|M)(l|L)?$)` which allows any file extension except HTML files.",
     action: parsers.arrayParser,
-    default: ['^[^hH][^tT][^mM][^lL]?$'],
+    default: ['^(?!(h|H)(t|T)(m|M)(l|L)?$)'],
   },
 };
 module.exports.DatabaseOptions = {

src/Options/docs.js

@@ -229,7 +229,7 @@
  * @property {Boolean} enableForAnonymousUser Is true if file upload should be allowed for anonymous users.
  * @property {Boolean} enableForAuthenticatedUser Is true if file upload should be allowed for authenticated users.
  * @property {Boolean} enableForPublic Is true if file upload should be allowed for anyone, regardless of user authentication.
- * @property {String[]} fileExtensions Sets the allowed file extensions for uploading files. The extension is defined as an array of file extensions, or a regex pattern.<br><br>It is recommended to restrict the file upload extensions as much as possible. HTML files are especially problematic as they may be used by an attacker who uploads a HTML form to look legitimate under your app's domain name, or to compromise the session token of another user via accessing the browser's local storage.<br><br>Defaults to `^[^hH][^tT][^mM][^lL]?$` which allows any file extension except HTML files.
+ * @property {String[]} fileExtensions Sets the allowed file extensions for uploading files. The extension is defined as an array of file extensions, or a regex pattern.<br><br>It is recommended to restrict the file upload extensions as much as possible. HTML files are especially problematic as they may be used by an attacker who uploads a HTML form to look legitimate under your app's domain name, or to compromise the session token of another user via accessing the browser's local storage.<br><br>Defaults to `^(?!(h|H)(t|T)(m|M)(l|L)?$)` which allows any file extension except HTML files.
  */
 
 /**

src/Options/index.js

@@ -576,8 +576,8 @@ export interface PasswordPolicyOptions {
 }
 
 export interface FileUploadOptions {
-  /* Sets the allowed file extensions for uploading files. The extension is defined as an array of file extensions, or a regex pattern.<br><br>It is recommended to restrict the file upload extensions as much as possible. HTML files are especially problematic as they may be used by an attacker who uploads a HTML form to look legitimate under your app's domain name, or to compromise the session token of another user via accessing the browser's local storage.<br><br>Defaults to `^[^hH][^tT][^mM][^lL]?$` which allows any file extension except HTML files.
+  /* Sets the allowed file extensions for uploading files. The extension is defined as an array of file extensions, or a regex pattern.<br><br>It is recommended to restrict the file upload extensions as much as possible. HTML files are especially problematic as they may be used by an attacker who uploads a HTML form to look legitimate under your app's domain name, or to compromise the session token of another user via accessing the browser's local storage.<br><br>Defaults to `^(?!(h|H)(t|T)(m|M)(l|L)?$)` which allows any file extension except HTML files.
-  :DEFAULT: ["^[^hH][^tT][^mM][^lL]?$"] */
+  :DEFAULT: ["^(?!(h|H)(t|T)(m|M)(l|L)?$)"] */
   fileExtensions: ?(string[]);
   /*  Is true if file upload should be allowed for anonymous users.
   :DEFAULT: false */