Issue 4450 - Prevent ElemHide filters with empty domains

lib/filterClasses.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2016 Eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 906 matching lines @@
     }
 
     if (id)
       selector = tagName + "." + id + additional + "," + tagName + "#" + id + additional;
     else if (tagName || additional)
       selector = tagName + additional;
     else
       return new InvalidFilter(text, "filter_elemhide_nocriteria");
   }
 
+  // We don't allow ElemHide filters which have any empty domains.
+  // Note: The ElemHide.prototype.domainSeparator is duplicated here, if that
+  // changes this must be changed too.
+  if (domain && /(^|,)~?(,|$)/.test(domain))
+    return new InvalidFilter(text, "filter_invalid_domain");
+
   if (isException)
     return new ElemHideException(text, domain, selector);
 
   let match = Filter.csspropertyRegExp.exec(selector);
   if (match)
   {
     // CSS property filters are inefficient so we need to make sure that
     // they're only applied if they specify active domains
     if (!/,[^~][^,.]*\.[^,]/.test("," + domain))
       return new InvalidFilter(text, "filter_cssproperty_nodomain");
@@ skipping 97 matching lines @@
     // several times on Safari, due to WebKit bug 132872
     let prop = Object.getOwnPropertyDescriptor(this, "regexpString");
     if (prop)
       return prop.value;
 
     let regexp = Filter.toRegExp(this.regexpSource);
     Object.defineProperty(this, "regexpString", {value: regexp});
     return regexp;
   }
 });