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Misc JS Tricks & Relevant Info

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Fuzzing de Javascript

Caracteres de Comentario JS Válidos

//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 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 de función

// 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

// 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)

Surrogate Pairs BF

Esta técnica no será muy útil para XSS, pero podría ser útil para evadir protecciones de WAF. Este código de Python recibe como entrada 2 bytes y busca pares sustitutos que tengan el primer byte como el último byte del par sustituto alto y el último byte como el último byte del par sustituto bajo.

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"))

Más información:

Fuzzing del 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

// 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

Fuzzing HTML

// 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. Verifica: https://portswigger-labs.net/hackability/inspector/?input=x.contentWindow&html=%3Ciframe%20src=//subdomain1.portswigger-labs.net%20id=x%3E

Archivos .map js

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 como NaN. Esto se puede utilizar para eliminar el contenido de variables del entorno.

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 no se proporciona nada, window será ese valor (a menos que se use strict mode).

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 de forma más sencilla (si las entiendes)

// 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 poder llamarlas. Por ejemplo, creando la función plusone:

// 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.

//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')

Ten en cuenta que usando bind puedes manipular el objeto this que se va a utilizar al llamar a la función.

Fuga de código de función

Si puedes acceder al objeto de una función, puedes obtener el código de esa función.

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 casos en los que la función no tiene nombre, aún puedes imprimir el código de la función desde su interior:

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

Algunas formas aleatorias de extraer el código de una función (incluso comentarios) de otra función:

(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.

// 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

// 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;
}
// 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 del navegador para probar payloads

//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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