> Cross-site scripting (XSS) is a type of computer security vulnerability typically found in web applications. XSS enables attackers to inject client-side scripts into web pages viewed by other users.
Cross-Site Scripting (XSS) is a type of computer security vulnerability typically found in web applications. XSS allows attackers to inject malicious code into a website, which is then executed in the browser of anyone who visits the site. This can allow attackers to steal sensitive information, such as user login credentials, or to perform other malicious actions.
There are 3 main types of XSS attacks:
* **Reflected XSS**: In a reflected XSS attack, the malicious code is embedded in a link that is sent to the victim. When the victim clicks on the link, the code is executed in their browser. For example, an attacker could create a link that contains malicious JavaScript, and send it to the victim in an email. When the victim clicks on the link, the JavaScript code is executed in their browser, allowing the attacker to perform various actions, such as stealing their login credentials.
* **Stored XSS**: In a stored XSS attack, the malicious code is stored on the server, and is executed every time the vulnerable page is accessed. For example, an attacker could inject malicious code into a comment on a blog post. When other users view the blog post, the malicious code is executed in their browsers, allowing the attacker to perform various actions.
* **DOM-based XSS**: is a type of XSS attack that occurs when a vulnerable web application modifies the DOM (Document Object Model) in the user's browser. This can happen, for example, when a user input is used to update the page's HTML or JavaScript code in some way. In a DOM-based XSS attack, the malicious code is not sent to the server, but is instead executed directly in the user's browser. This can make it difficult to detect and prevent these types of attacks, because the server does not have any record of the malicious code.
To prevent XSS attacks, it is important to properly validate and sanitize user input. This means ensuring that all input meets the necessary criteria, and removing any potentially dangerous characters or code. It is also important to escape special characters in user input before rendering it in the browser, to prevent the browser from interpreting it as code.
When exploiting an XSS vulnerability, it’s more effective to demonstrate a complete exploitation scenario that could lead to account takeover or sensitive data exfiltration. Instead of simply reporting an XSS with an alert payload, aim to capture valuable data, such as payment information, personal identifiable information (PII), session cookies, or credentials.
Modern applications with content hosting can use [sandbox domains][sandbox-domains]
> to safely host various types of user-generated content. Many of these sandboxes are specifically meant to isolate user-uploaded HTML, JavaScript, or Flash applets and make sure that they can't access any user data.
For this reason, it's better to use `alert(document.domain)` or `alert(window.origin)` rather than `alert(1)` as default XSS payload in order to know in which scope the XSS is actually executing.
While `alert()` is nice for reflected XSS it can quickly become a burden for stored XSS because it requires to close the popup for each execution, so `console.log()` can be used instead to display a message in the console of the developer console (doesn't require any interaction).
More comprehensive payload with svg tag attribute, desc script, foreignObject script, foreignObject iframe, title script, animatetransform event and simple script. Codename: red ligthning. Author: noraj.
Including a remote SVG fragment in a SVG works but won't trigger the XSS embedded in the remote SVG element because it's impossible to add vulnerable attribute on a polygon/rect/etc since the `style` attribute is no longer a vector on modern browsers. Author: noraj.
> XSS Hunter allows you to find all kinds of cross-site scripting vulnerabilities, including the often-missed blind XSS. The service works by hosting specialized XSS probes which, upon firing, scan the page and send information about the vulnerable page to the XSS Hunter service.
You can use a [Data grabber for XSS](#data-grabber-for-xss) and a one-line HTTP server to confirm the existence of a blind XSS before deploying a heavy blind-XSS testing tool.
Use browsers quirks to recreate some HTML tags when it is inside an `element.innerHTML`.
Mutated XSS from Masato Kinugawa, used against DOMPurify component on Google Search. Technical blogposts available at https://www.acunetix.com/blog/web-security-zone/mutation-xss-in-google-search/ and https://research.securitum.com/dompurify-bypass-using-mxss/.
- [Abusing XSS Filter: One ^ leads to XSS(CVE-2016-3212) - Masato Kinugawa's (@kinugawamasato) - July 15, 2016](http://mksben.l0.cm/2016/07/xxn-caret.html)
- [Account Recovery XSS - Gábor Molnár - April 13, 2016](https://sites.google.com/site/bughunteruniversity/best-reports/account-recovery-xss)
- [An XSS on Facebook via PNGs & Wonky Content Types - Jack Whitton (@fin1te) - January 27, 2016](https://whitton.io/articles/xss-on-facebook-via-png-content-types/)
- [Combination of techniques lead to DOM Based XSS in Google - Sasi Levi - September 19, 2016](http://sasi2103.blogspot.sg/2016/09/combination-of-techniques-lead-to-dom.html)
- [Frans Rosén on how he got Bug Bounty for Mega.co.nz XSS - Frans Rosén - February 14, 2013](https://labs.detectify.com/2013/02/14/how-i-got-the-bug-bounty-for-mega-co-nz-xss/)
- [Google XSS Turkey - Frans Rosén - June 6, 2015](https://labs.detectify.com/2015/06/06/google-xss-turkey/)
- [How I found a $5,000 Google Maps XSS (by fiddling with Protobuf) - Marin Moulinier - March 9, 2017](https://medium.com/@marin_m/how-i-found-a-5-000-google-maps-xss-by-fiddling-with-protobuf-963ee0d9caff#.cktt61q9g)
- [Killing a bounty program, Twice - Itzhak (Zuk) Avraham and Nir Goldshlager - May 2012](http://conference.hitb.org/hitbsecconf2012ams/materials/D1T2%20-%20Itzhak%20Zuk%20Avraham%20and%20Nir%20Goldshlager%20-%20Killing%20a%20Bug%20Bounty%20Program%20-%20Twice.pdf)
- [mXSS Attacks: Attacking well-secured Web-Applications by using innerHTML Mutations - Mario Heiderich, Jörg Schwenk, Tilman Frosch, Jonas Magazinius, Edward Z. Yang - September 26, 2013](https://cure53.de/fp170.pdf)
- [postMessage XSS on a million sites - Mathias Karlsson - December 15, 2016](https://labs.detectify.com/2016/12/15/postmessage-xss-on-a-million-sites/)
- [RPO that lead to information leakage in Google - @filedescriptor - July 3, 2016](https://web.archive.org/web/20220521125028/https://blog.innerht.ml/rpo-gadgets/)
- [Secret Web Hacking Knowledge: CTF Authors Hate These Simple Tricks - Philippe Dourassov - May 13, 2024](https://youtu.be/Sm4G6cAHjWM)
- [Stealing contact form data on www.hackerone.com using Marketo Forms XSS with postMessage frame-jumping and jQuery-JSONP - Frans Rosén (fransrosen) - February 17, 2017](https://hackerone.com/reports/207042)
- [Stored XSS affecting all fantasy sports [*.fantasysports.yahoo.com] - thedawgyg - December 7, 2016](https://web.archive.org/web/20161228182923/http://dawgyg.com/2016/12/07/stored-xss-affecting-all-fantasy-sports-fantasysports-yahoo-com-2/)
- [Stored XSS in *.ebay.com - Jack Whitton (@fin1te) - January 27, 2013](https://whitton.io/archive/persistent-xss-on-myworld-ebay-com/)
- [Stored XSS In Facebook Chat, Check In, Facebook Messenger - Nirgoldshlager - April 17, 2013](http://web.archive.org/web/20130420095223/http://www.breaksec.com/?p=6129)
- [Stored XSS on developer.uber.com via admin account compromise in Uber - James Kettle (@albinowax) - July 18, 2016](https://hackerone.com/reports/152067)
- [Stored XSS on Snapchat - Mrityunjoy - February 9, 2018](https://medium.com/@mrityunjoy/stored-xss-on-snapchat-5d704131d8fd)
- [Stored XSS, and SSRF in Google using the Dataset Publishing Language - Craig Arendt - March 7, 2018](https://s1gnalcha0s.github.io/dspl/2018/03/07/Stored-XSS-and-SSRF-Google.html)
- [Tricky HTML Injection and Possible XSS in sms-be-vip.twitter.com - Ahmed Aboul-Ela (@aboul3la) - July 9, 2016](https://hackerone.com/reports/150179)
- [Twitter XSS by stopping redirection and javascript scheme - Sergey Bobrov (bobrov) - September 30, 2017](https://hackerone.com/reports/260744)
- [Uber Bug Bounty: Turning Self-XSS into Good XSS - Jack Whitton (@fin1te) - March 22, 2016](https://whitton.io/articles/uber-turning-self-xss-into-good-xss/)
- [Uber Self XSS to Global XSS - httpsonly - August 29, 2016](https://httpsonly.blogspot.hk/2016/08/turning-self-xss-into-good-xss-v2.html)
- [Unleashing an Ultimate XSS Polyglot - Ahmed Elsobky - February 16, 2018](https://github.com/0xsobky/HackVault/wiki/Unleashing-an-Ultimate-XSS-Polyglot)
- [Using a Braun Shaver to Bypass XSS Audit and WAF - Frans Rosen - April 19, 2016](http://web.archive.org/web/20160810033728/https://blog.bugcrowd.com/guest-blog-using-a-braun-shaver-to-bypass-xss-audit-and-waf-by-frans-rosen-detectify)
- [Ways to alert(document.domain) - Tom Hudson (@tomnomnom) - February 22, 2018](https://gist.github.com/tomnomnom/14a918f707ef0685fdebd90545580309)
- [XSS by Tossing Cookies - WeSecureApp - July 10, 2017](https://wesecureapp.com/blog/xss-by-tossing-cookies/)
- [XSS ghettoBypass - d3adend - September 25, 2015](http://d3adend.org/xss/ghettoBypass)
- [XSS in Uber via Cookie - zhchbin - August 30, 2017](http://zhchbin.github.io/2017/08/30/Uber-XSS-via-Cookie/)
- [XSS on any Shopify shop via abuse of the HTML5 structured clone algorithm in postMessage listener - Luke Young (bored-engineer) - May 23, 2017](https://hackerone.com/reports/231053)
- [XSS via Host header - www.google.com/cse - Michał Bentkowski - April 22, 2015](http://blog.bentkowski.info/2015/04/xss-via-host-header-cse.html)
- [Xssing Web With Unicodes - Rakesh Mane - August 3, 2017](http://blog.rakeshmane.com/2017/08/xssing-web-part-2.html)
- [Yahoo Mail stored XSS - Jouko Pynnönen - January 19, 2016](https://klikki.fi/adv/yahoo.html)
- [Yahoo Mail stored XSS #2 - Jouko Pynnönen - December 8, 2016](https://klikki.fi/adv/yahoo2.html)