# Trucos JS Varios e Información Relevante

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## Fuzzing de Javascript

### Caracteres de Comentario JS Válidos
```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

// From: Heyes, Gareth. JavaScript for hackers: Learn to think like a hacker (p. 43). Kindle Edition.
log=[];
for(let i=0;i<=0xff;i++){
for(let j=0;j<=0xfff;j++){
try {
eval(`${String.fromCodePoint(i,j)}%$£234$`)
log.push([i,j])
}catch(e){}
}
}
console.log(log)//[35,33],[47,47]
```
### Caracteres de Nueva Línea JS Válidos
```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
```
### Espacios JS Válidos en la llamada a función
```javascript
// Heyes, Gareth. JavaScript for hackers: Learn to think like a hacker (pp. 40-41). Kindle Edition.

// Check chars that can be put in between in func name and the ()
function x(){}

log=[];
for(let i=0;i<=0x10ffff;i++){
try {
eval(`x${String.fromCodePoint(i)}()`)
log.push(i)
}catch(e){}
}

console.log(log)v//9,10,11,12,13,32,160,5760,8192,8193,8194,8195,8196,8197,8198,8199,8200,8201,8202,813 232,8233,8239,8287,12288,65279
```
### **Caracteres válidos para generar cadenas**
```javascript
// Heyes, Gareth. JavaScript for hackers: Learn to think like a hacker (pp. 41-42). Kindle Edition.

// Check which pairs of chars can make something be a valid string
log = []
for (let i = 0; i <= 0x10ffff; i++) {
try {
eval(`${String.fromCodePoint(i)}%$£234${String.fromCodePoint(i)}`)
log.push(i)
} catch (e) {}
}
console.log(log) //34,39,47,96
//single quote, quotes, backticks & // (regex)
```
### **Pares Suplementarios BF**

Esta técnica no será muy útil para XSS, pero podría ser útil para eludir las protecciones de WAF. Este código de python recibe como entrada 2 bytes y busca pares suplementarios que tengan el primer byte como el último byte del par suplementario alto y el último byte como el último byte del par suplementario bajo.
```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"))
```
### `javascript{}:` Fuzzing de Protocolo
```javascript
// Heyes, Gareth. JavaScript for hackers: Learn to think like a hacker (p. 34). Kindle Edition.
log=[];
let anchor = document.createElement('a');
for(let i=0;i<=0x10ffff;i++){
anchor.href = `javascript${String.fromCodePoint(i)}:`;
if(anchor.protocol === 'javascript:') {
log.push(i);
}
}
console.log(log)//9,10,13,58
// Note that you could BF also other possitions of the use of multiple chars

// Test one option
let anchor = document.createElement('a');
anchor.href = `javascript${String.fromCodePoint(58)}:alert(1337)`;
anchor.append('Click me')
document.body.append(anchor)

// Another way to test
<a href="&#12;javascript:alert(1337)">Test</a>
```
### Fuzzing de URL
```javascript
// Heyes, Gareth. JavaScript for hackers: Learn to think like a hacker (pp. 36-37). Kindle Edition.

// Before the protocol
a = document.createElement("a")
log = []
for (let i = 0; i <= 0x10ffff; i++) {
a.href = `${String.fromCodePoint(i)}https://hacktricks.xyz`
if (a.hostname === "hacktricks.xyz") {
log.push(i)
}
}
console.log(log) //0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32

// Between the slashes
a = document.createElement("a")
log = []
for (let i = 0; i <= 0x10ffff; i++) {
a.href = `/${String.fromCodePoint(i)}/hacktricks.xyz`
if (a.hostname === "hacktricks.xyz") {
log.push(i)
}
}
console.log(log) //9,10,13,47,92
```
### HTML Fuzzing
```javascript
// Heyes, Gareth. JavaScript for hackers: Learn to think like a hacker (p. 38). Kindle Edition.

// Fuzzing chars that can close an HTML comment

let log = []
let div = document.createElement("div")
for (let i = 0; i <= 0x10ffff; i++) {
div.innerHTML = `<!----${String.fromCodePoint(i)}><span></span>-->`
if (div.querySelector("span")) {
log.push(i)
}
}
console.log(log) //33,45,62
```
## **Analizando atributos**

La herramienta **Hackability inspector** de Portswigger ayuda a **analizar** los **atributos** de un objeto javascript. Ver: [https://portswigger-labs.net/hackability/inspector/?input=x.contentWindow\&html=%3Ciframe%20src=//subdomain1.portswigger-labs.net%20id=x%3E](https://portswigger-labs.net/hackability/inspector/?input=x.contentWindow&html=%3Ciframe%20src=//subdomain1.portswigger-labs.net%20id=x%3E)

## **.map archivos js**

- Truco para descargar archivos .map js: [https://medium.com/@bitthebyte/javascript-for-bug-bounty-hunters-part-2-f82164917e7](https://medium.com/@bitthebyte/javascript-for-bug-bounty-hunters-part-2-f82164917e7)
- Puedes usar esta herramienta para analizar estos archivos [https://github.com/paazmaya/shuji](https://github.com/paazmaya/shuji)

## "--" Asignación

El operador de decremento `--` también es una asignación. Este operador toma un valor y luego lo decrementa en uno. Si ese valor no es un número, se establecerá en `NaN`. Esto se puede usar para **eliminar el contenido de las variables del entorno**.

![](<../../images/image (993).png>)

![](<../../images/image (329).png>)

## Trucos de Funciones

### .call y .apply

El método **`.call`** de una función se utiliza para **ejecutar la función**.\
El **primer argumento** que espera por defecto es el **valor de `this`** y si **nada** se proporciona, **`window`** será ese valor (a menos que se use **`modo estricto`**).
```javascript
function test_call() {
console.log(this.value) //baz
}
new_this = { value: "hey!" }
test_call.call(new_this)

// To pass more arguments, just pass then inside .call()
function test_call() {
console.log(arguments[0]) //"arg1"
console.log(arguments[1]) //"arg2"
console.log(this) //[object Window]
}
test_call.call(null, "arg1", "arg2")

// If you use the "use strict" directive "this" will be null instead of window:
function test_call() {
"use strict"
console.log(this) //null
}
test_call.call(null)

//The apply function is pretty much exactly the same as the call function with one important difference, you can supply an array of arguments in the second argument:
function test_apply() {
console.log(arguments[0]) //"arg1"
console.log(arguments[1]) //"arg2"
console.log(this) //[object Window]
}
test_apply.apply(null, ["arg1", "arg2"])
```
### Funciones de flecha

Las funciones de flecha te permiten generar funciones en una sola línea más fácilmente (si las entiendes)
```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;
```
Entonces, la mayoría de las funciones anteriores son en realidad inútiles porque no las estamos guardando en ningún lugar para guardarlas y llamarlas. Ejemplo creando la función `plusone`:
```javascript
// Traductional
function plusone(a) {
return a + 1
}

//Arrow
plusone = (a) => a + 100
```
### Función bind

La función bind permite crear una **copia** de una **función modificando** el **objeto `this`** y los **parámetros** dados.
```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")
```
> [!NOTE]
> Tenga en cuenta que al usar **`bind`** puede manipular el objeto **`this`** que se va a utilizar al llamar a la función.

### Fuga de código de función

Si puede **acceder al objeto** de una función, puede **obtener el código** de esa función.
```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
```
En los casos en que la **función no tiene ningún nombre**, aún puedes imprimir el **código de la función** desde dentro:
```javascript
;(function () {
return arguments.callee.toString()
})()(function () {
return arguments[0]
})("arg0")
```
Algunas **maneras aleatorias** de **extraer el código** de una función (incluso comentarios) de otra función:
```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 */
})()
```
## Escape de Sandbox - Recuperando el objeto window

El objeto Window permite acceder a funciones definidas globalmente como alert o eval.
```javascript
// Some ways to access window
window.eval("alert(1)")
frames
globalThis
parent
self
top //If inside a frame, this is top most window

// Access window from document
document.defaultView.alert(1)
// Access document from a node object
node = document.createElement('div')
node.ownerDocument.defaultView.alert(1)

// There is a path property on each error event whose last element is the window
<img src onerror=event.path.pop().alert(1337)>
// In other browsers the method is
<img src onerror=event.composedPath().pop().alert(1337)>
// In case of svg, the "event" object is called "evt"
<svg><image href=1 onerror=evt.composedPath().pop().alert(1337)>

// Abusing Error.prepareStackTrace to get Window back
Error.prepareStackTrace=function(error, callSites){
2   callSites.shift().getThis().alert(1337);
3 };
4 new Error().stack

// From an HTML event
// Events from HTML are executed in this context
with(document) {
with(element) {
//executed event
}
}
// Because of that with(document) it's possible to access properties of document like:
<img src onerror=defaultView.alert(1337)>
<img src onerror=s=createElement('script');s.append('alert(1337)');appendChild(s)>
```
## Punto de interrupción en el acceso al valor
```javascript
// Stop when a property in sessionStorage or localStorage is set/get
// via getItem or setItem functions
sessionStorage.getItem = localStorage.getItem = function (prop) {
debugger
return sessionStorage[prop]
}

localStorage.setItem = function (prop, val) {
debugger
localStorage[prop] = val
}
```

```javascript
// Stop when anyone sets or gets the property "ppmap" in any object
// For example sessionStorage.ppmap
// "123".ppmap
// Useful to find where weird properties are being set or accessed
// or to find where prototype pollutions are occurring

function debugAccess(obj, prop, debugGet = true) {
var origValue = obj[prop]

Object.defineProperty(obj, prop, {
get: function () {
if (debugGet) debugger
return origValue
},
set: function (val) {
debugger
origValue = val
},
})
}

debugAccess(Object.prototype, "ppmap")
```
## Acceso automático al navegador para probar cargas útiles
```javascript
//Taken from https://github.com/svennergr/writeups/blob/master/inti/0621/README.md
const puppeteer = require("puppeteer")

const realPasswordLength = 3000
async function sleep(ms) {
return new Promise((resolve) => setTimeout(resolve, ms))
}

;(async () => {
const browser = await puppeteer.launch()
const page = await browser.newPage()
//Loop to iterate through different values
for (let i = 0; i < 10000; i += 100) {
console.log(`Run number ${i}`)
const input = `${"0".repeat(i)}${realPasswordLength}`
console.log(
`  https://challenge-0621.intigriti.io/passgen.php?passwordLength=${input}&allowNumbers=true&allowSymbols=true&timestamp=1624556811000`
)
//Go to the page
await page.goto(
`https://challenge-0621.intigriti.io/passgen.php?passwordLength=${input}&allowNumbers=true&allowSymbols=true&timestamp=1624556811000`
)
//Call function "generate()" inside the page
await page.evaluate("generate()")
//Get node inner text from an HTML element
const passwordContent = await page.$$eval(
".alert .page-content",
(node) => node[0].innerText
)
//Transform the content and print it in console
const plainPassword = passwordContent.replace("Your password is: ", "")
if (plainPassword.length != realPasswordLength) {
console.log(i, plainPassword.length, plainPassword)
}

await sleep(1000)
}
await browser.close()
})()
```
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