[[ wiki ]] added new attack examples

domc_wiki/index.md

@@ -37,19 +37,19 @@ Accordingly, web browsers map HTML elements to JavaScript objects automatically
 
 
 
-## Attack Example
+## Attack Examples
 
-Consider the following code listing. 
+When an [undefined variable](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/undefined) and an HTML markup have the same name, the browser replaces the content of the variable with the DOM object mirroring the markup type. 
+
+**Example 1:** 
 
 ```js
 1. var s = document.createElement('script');
-2 let config = window.globalConfig || {href: 'script.js'};
-3 s.src = config.href;
-4 document.body.appendChild(s);
+2. let config = window.globalConfig || {href: 'script.js'};
+3. s.src = config.href;
+4. document.body.appendChild(s);
 ```
 
-When an [undefined variable](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/undefined) and an HTML markup have the same name, the browser replaces the content of the variable with the DOM object mirroring the markup type. 
-
 The snippet shows a vulnerable code, which loads a script whose URL is stored in a global configuration object, i.e., `window.globalConfig`. Specifically, the code first creates a `script` tag (line 1), and then, it retrieves the global configuration object and stores it in a local variable `config` (line 2). If the configuration object does not exist, it uses a minimal default configuration, i.e., `{href: script.js'}` (line 2). Then, the program sets the `src` attribute of the newly created script tag to the `href` property of the configuration object (line 3) and appends the new script to the DOM tree, resulting in the execution of the script (line 4). 
 
 The vulnerability originates in the assignment in line 2 because
@@ -61,6 +61,33 @@ When parsing such a markup code, the browser maps the anchor tag element to the
 **Note.** Attackers can abuse named property accesses in other ways, where instead of overwriting variables by HTML nodes, they can overshadow [browser APIs](https://developer.mozilla.org/en-US/docs/Web/API). For example, if the attacker inserts a markup with `id=getElementbyId` in DOM, then the API `document.getElementbyId` no longer refers to the built-in API for finding an element in the DOM tree, but rather mirrors the DOM element with id `getElementbyId` in the DOM tree. This behaviour is due to the so-called [named property visibility algorithm](https://webidl.spec.whatwg.org/#legacy-platform-object-abstract-ops).
 
 
+**Example 2:** 
+
+```js
+1. document.conf = {};
+2. const queryParams = new URLSearchParams(window.location.search);
+3. if(isTrustedOrigin(queryParams.get('next'))){
+4. 		document.conf.src = queryParams.get('next');
+5. }
+6. // [...]
+7. let next = document.conf.src || 'https://benign1.com/index.html';
+8. window.location.href = next;
+9. // [...]
+10. function isTrustedOrigin(url){ 
+11.	  let targetOrigin = new URL(url).origin;
+12.	  let trustedOrigins= [
+13.	    new URL('https://benign1.com').origin, 
+14.		new URL('https://benign2.com').origin
+15.	  ];
+16.	  if(trustedOrigins.indexOf(targetOrigin) !== -1) return true;
+17.	  return false;
+18. }
+```
+
+The snippet above reads the value of a query parameter `next`, and if it belongs to a trusted domain, it stores it globally in `document.conf.src` (lines 1-4). Then, it redirects the page to `document.conf.src` or a default value (line 6).
+
+This script is vulnerable because it ignores the fact that assignments to `document` are always overshadowed by DOM Clobbering. For example, if attackers inject `<img name="conf" src="javascript:alert(1)">`, the `document.conf` would point to the image tag, so `document.conf.src` is an attacker-controlled JavaScript payloa. Hence, this results in XSS when assigned to the top window location (line 8).
+
 
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