Xss Cheat Sheet Github

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Here we are going to see about most important XSS Cheat Sheet. What is XSS(Cross Site Scripting)? An attacker can inject untrusted snippets of JavaScript into your application without validation. This JavaScript is then executed by the victim who is visiting the target site. XSS classified into three types and these XSS Cheat Sheet will help to find the XSS vulnerabilities for Pentesters. Introduction This cheat sheet is focused on providing developer guidance on Clickjack/UI Redressattack prevention. The most popular way to defend against Clickjacking is to include some sort of 'frame-breaking' functionality which prevents other web pages from framing the site you wish to defend. XSS cheat sheet. Contribute to reeye/xss development by creating an account on GitHub.

  • XSS Filter Evasion Cheat Sheet GitHub. XSS Filter Evasion Cheat Sheet. Inject this string, and in most cases where a script is vulnerable with no special XSS vector requirements the word 'XSS' will pop up.
  • Cross-site Scripting (XSS). There is an Authentication Cheat Sheet. Insecure Direct Object Reference or Forceful Browsing. There are emerging tools that can be used to track security issues in dependency sets, like automated scanning from GitHub and GitLab.

Introduction

Froala WYSIWYG HTML Editor is a lightweight WYSIWYG HTML Editor written in JavaScript that enables rich text editing capabilities for web applications [1]. Froala sanitizes the user input in order to prevent cross-site scripting attacks [2].

During a web application penetration test at Compass, I found a DOM-based cross-site scripting (XSS) [3] in the Froala WYSIWYG HTML Editor. HTML code in the editor is not correctly sanitized when inserted into the DOM. This allows an attacker that can control the editor content to execute arbitrary JavaScript in the
context of the victim’s session.

0-Day

In June 2020, Michał Bentkowski [4] from Securitum [5] released some research about copy-paste XSS [6], which is definitively interesting to read! During his research, he identified an XSS issue in Froala. Froala could not tell Michał when they will fix the issue and so he published it after a while.

I discovered another XSS issue, informed Froala in December 2019 and they told me it will be fixed soon. However, it’s still not fixed at the moment. Froala told me the issue would be fixed in Q2 of 2020 but this was not the case. Now when Q2 has ended and after more than 200 days, I decided to also publish this finding.

Affected

  • All versions of the Froala WYSIWYG HTML Editor

The issue was found in December 2019 in version 3.0.6 and was still not fixed in July 2020 in version 3.1.1.

Technical Summary

It’s possible to perform DOM based XSS in the Froala editor by inserting the <iframe> tag and the srcdoc attribute into the editor:

This can be verified by inserting the payload into the “Code View” of the editor.

In this case, this is would be a self-XSS because the users would only attack themselves. However, it could be possible that untrusted data from a non-controlled source is loaded into the editor in order to exploit it. An example could be a web application where multiple users can edit the same content using this editor.

You can try it out online here: https://jsfiddle.net/xc4dem53/:

An attacker can use this to execute own JavaScript code in the session of the user. This can be abused to read the content of the victim’s account, use the session to make further requests to the web application or read the cookies or web storage.

Technical Details & PoC

Correct Behavior

According to the Froala tech support page “Why is the <script> tag being removed?”, the <script> tag is removed in order to prevent possible XSS attacks [2]:

Other XSS payloads that use other HTML tags and event handlers are also removed from the DOM before they are inserted.

This can be verified using a PoC hosted on poc.example.net that inserts potentially untrusted data with a <script> tag into the editor:

You can try it out online here: https://jsfiddle.net/62fczbao/:

The JavaScript console shows that legit HTML tags like <s> or <u> were inserted into the DOM but the <script> tag was correctly removed (as expected) and therefore the JavaScript was not executed:

This is usually where the game starts to find a working XSS, e.g. by inserting an <img> tag with an onerror event handler as an XSS vector:

You can try it out online here: https://jsfiddle.net/52pxqv1w/:

The JavaScript console again shows that the legit HTML tags were inserted and also the <img> tag, but without the used onerror event handler. Therefore, the JavaScript was not executed:

This shows that it’s not possible to load and execute common XSS payloads into the editor.

XSS Bypass

Xss Cheat Codes

I tried every event handler from the awesome PortSwigger XSS cheat sheet [7], but all of them were blocked. Thanks to the XSS cheat sheet, I found an HTML tag with an attribute that does not start with on, which can execute JavaScript in the origin of the website. This tag was not filtered. It’s the <iframe> tag with the srcdoc attribute. The srcdoc attribute specifies the HTML content of the page to show in the inline frame [8]. This can be used to embed JavaScript code. The code runs in the origin of the website where the iframe is embedded.

Working XSS payload:

You can try it out online here: https://jsfiddle.net/bu6ntxsj/:

The JavaScript console shows that the <iframe> tag with the srcdoc attribute was inserted into the DOM without sanitizing. Also the content of the iframe with the <img> tag and the onerror event handler was not sanitized. Further, the origin on which the PoC website is hosted is printed:

Therefore, this shows that the following XSS payload can be used in order to inject and execute JavaScript into the DOM, which results in a DOM-based XSS:

Note: The <img> tag with the onerror event handler is only the data content of the srcdoc attribute and no code for the browser. This is rendered into code later when the content of the iframe is built.

The injected JavaScript code runs in the origin of the website where the Froala editor is running. The next section explains why I mention this explicitly.

XSS with Undefined / Empty Origin

There are several issues marked as open and fixed in the Froala GitHub repository regarding XSS [9]. However, most of these XSS are running in another origin as the website where the editor is loaded.

Example #1

For example, the issue #3270 [10] that is marked as closed and uses an embedded object (<embed> tag) in order to execute JavaScript:

Example payload:

The base64 decoded payload is an SVG image containing JavaScript:

You can try it out online here: https://jsfiddle.net/txr6upgc/:

The JavaScript console shows that the code is executed but the origin is undefined:

Example #2

Another example is the issue #3039 [11] that is marked as closed uses the <object> tag to embed HTML / JavaScript code:

Example payload (it’s not necessarily needed to base64 encode the payload):

You can try it out online here: https://jsfiddle.net/br6dq8uf/:

The JavaScript console shows that the code is executed but the origin is empty:

Xss Cheat Sheet 2020

Exploiting XSS with Undefined / Empty Origins

Because the origin is not the same as where the PoC is hosted, it’s not a typical XSS where an attacker could read the content of the victim’s website, use the session to make further requests or access the cookies or web storage.

It is however still possible to perform arbitrary redirects to other websites using the reference to the window.top.location.

This does not work in JSFiddle for some reason, but you can create the following attack page and host it for yourself.

Redirect using the <object> tag:

Demo:

The same can be done using the <embed> tag:

Base64 payload (so you don’t have to escape everything in the attack page):

Demo:

This is not as nice and powerful as the “real” XSS attack from the beginning, but still something 😉.

Xss Cheat Sheet Github 2019

If you have other ideas of how such limited JavaScript injection can be exploited, let me know in the comments or ping me on Twitter (@mindfuckup)!

Remediation

This XSS issue is not fixed. The vendor can’t tell any exact release date for a fixed version.

Xss Attack Cheat Sheet

Therefore, only trusted data or data that is already sanitized should be loaded into the editor.

Update (2021-04-14)

This XSS was fixed in version 3.2.3:

Release: https://github.com/froala/wysiwyg-editor/releases/tag/v3.2.3

The XSS is not triggered anymore. You can try it out here: https://jsfiddle.net/bu6ntxsj/.

Xss Cheat Sheet Github

Xss Cheat Sheet Pdf

Advisory

Xss Payload Cheat Sheet Github

References

  • [1] https://froala.com/wysiwyg-editor/
  • [2] https://wysiwyg-editor.froala.help/hc/en-us/articles/115000428829-Why-is-the-script-tag-being-removed-
  • [3] https://portswigger.net/web-security/cross-site-scripting/dom-based
  • [4] https://twitter.com/securitymb
  • [5] https://securitum.pl/
  • [6] https://research.securitum.com/the-curious-case-of-copy-paste/
  • [7] https://portswigger.net/web-security/cross-site-scripting/cheat-sheet
  • [8] https://www.w3schools.com/tags/att_iframe_srcdoc.asp
  • [9] https://github.com/froala/wysiwyg-editor/issues?q=is%3Aissue+xss
  • [10] https://github.com/froala/wysiwyg-editor/issues/3270
  • [11] https://github.com/froala/wysiwyg-editor/issues/3039