General purpose JavaScript deobfuscator

A simple but powerful deobfuscator to remove common JavaScript obfuscation techniques.
Open an issue if there is a feature you think should be implemented.

Online version at deobfuscate.io

Features

* Unpacks arrays containing literals (strings, numbers etc) and replaces all references to them
* Removes simple proxy functions (calls to another function), array proxy functions and arithmetic proxy functions (binary expressions)
* Simplifies arithmetic expressions
* Simplifies string concatenation
* Renames unreadable hexadecimal identifiers (e.g. _0xca830a)
* Converts computed to static member expressions and beautifies the code
Experimental* function evaluation

Examples

See bottom for more complicated example with features chained together.

$3

Before
``javascript
const a = ['\x20', '\x57\x6f\x72\x6c\x64', '\x48\x65\x6c\x6c\x6f'];

console.log(a[2] + a[0] + a[1]);
`

After
`javascript
console.log("Hello" + " " + "World");
`




$3

#### An example with simple proxy functions for other functions

Before
`javascript
function a(b, c) {
return someFunction(b, c);
}

const result = a(5, 6);
`

After
`javascript
const result = someFunction(5, 6);
`




#### An example with proxy functions for arithmetic

Before
`javascript
function a(b, c) {
return c + 2 * b;
}

const result = a(5, 6);
`

After
`javascript
const result = 6 + 2 * 5;
`




#### An example with chained proxy functions

Before
`javascript
function a(b, c) {
return c + 2 * b;
}
function b(c, d) {
return a(c, d);
}
function c(d, e) {
return b(d, e);
}

const result = c(5, 6);
`

After
`javascript
const result = 6 + 2 * 5;
`




$3

#### An example with numbers

Before
`javascript
let total = 0x2 0x109e + -0xc -0x16a + -0x3234;
for (let i = 0x1196 + 0x97b 0x3 + -0x2e07; i < -0x95 -0x38 + -0x1a75 + -0x619; i++) {
total += i;
}
`

After
`javascript
let total = 0;
for (let i = 0; i < 10; i++) {
total += i;
}
`



#### An example with strings.

Before
`javascript
console.log('He' + 'll' + 'o' + ' Wo' + 'r' + 'ld');
`

After
`javascript
console.log("Hello World");
`




$3

All these features can be chained together to simplify code.

Before
`javascript
const ar = ['\x48\x65\x6c\x6c\x6f', 0x95, '\x20', 0x1a75, '\x57\x6f\x72\x6c\x64', -0x53, '\x6c\x6f\x67']
const a = function(b, c) {
return c + 2 * b;
}, b = function(c, d) {
return a(c, d);
}, c = function(d, e) {
return b(d, e);
};
const message = ar[0] + ar[2] + ar[4];
const result = c(ar[1] 0x38 + ar[3] + 0x619, 0x12 ar[5] + 0x1a13 + 0x621);
console[ar[6]](message + ' ' + result);
`

After
`javascript
const message = "Hello World";
const result = 40106;
console.log(message + " " + result);
`

Advanced Usage

$3

Often obfuscated scripts don't just use an array of strings, instead they have string decoder functions that execute more complex logic, such as the example below.

`javascript
function _0x29e92(_0x337a9) {
const _0x38a2db = ['\x48\x65\x6c\x6c\x6f', '\x20', '\x57\x6f\x72\x6c\x64'];
const _0x9ca21 = _0x337a9 - 0x1;
const _0xa8291 = _0x38a2db[_0x9ca21];
return _0xa8291;
}

const _0x78e2 = _0x29e92(1) + _0x29e92(2) + _0x29e92(3);
console.log(_0x78e2);
`

To tell the deobfuscator to execute this function, you can use the "#execute" directive like so:

`javascript
function _0x29e92(_0x337a9) {
"#execute";
const _0x38a2db = ['\x48\x65\x6c\x6c\x6f', '\x20', '\x57\x6f\x72\x6c\x64'];
const _0x9ca21 = _0x337a9 - 0x1;
const _0xa8291 = _0x38a2db[_0x9ca21];
return _0xa8291;
}

const _0x78e2 = _0x29e92(1) + _0x29e92(2) + _0x29e92(3);
console.log(_0x78e2);
`

The deobfuscator will then evaluate this function and attempt to replace any calls to it with the correct values:

`javascript
const a = "Hello World";
console.log(a);
``

A few important points about function evaluation:
* BE CAREFUL when using function evaluation, this executes whatever functions you specify on your local machine so make sure those functions are not doing anything malicious.
* This feature is still somewhat experimental, it's probably easier to use via the CLI as it's easier to find errors than the online version.
* If the function is not a function declaration (i.e. a function expression or an arrow function expression) then the deobfuscator will not be able to detect the name of it automatically. To provide it use "#execute[name=FUNC_NAME]" directive.
* You may need to modify the function to ensure it relies on no external variables (i.e. move a string array declaration inside the function) and handle any extra logic like string array rotation first.
* You must first remove any anti tampering mechanisms before using function evaluation, otherwise it may cause an infinite loop.

To Run

Put the obfuscated script in input/source.js and run:

npm start

Or use the online version at deobfuscate.io