pp-finder

Prototype pollution finder tool for javascript. pp-finder lets you find prototype pollution candidates in your code. The main purpose of this tool is to help hackers in there prototype pollution researchs by highlighting potential candidate in the source code.

For instance, the following candidate will be highlighted by pp-finder:

if (options.exec) child_process.exec(options.exec);

Installation

NPM

$ npm install -g pp-finder

yarn

$ yarn global add pp-finder

Getting started

For instance, let's find candidates in the popular express library:

$ mkdir -p target/express
$ cd target/express
$ yarn add express
$ # now write a very basic express application

const express = require("express");

const app = express();
const port = 3000;

app.get("/", (req, res) => {
  res.send("Hello World!");
});

app.listen(port, () => {
  console.log(`Example app listening on port ${port}`);
});

To hunt for prototype pollution gadgets, pp-finder will parse the javascript source code of every file it finds in the provided directory.

It will use the --experimental-loader options from nodejs to perform ast modifications on the fly.

$ node --experimental-loader pp-finder ./index.js

From now, if you run the application, it will output all the available candidates:

[PP][IsIn "colors"] node_modules/debug/src/node.js:76:22
[PP][ForIn] node_modules/safer-buffer/safer.js:12:13
[PP][IsIn "colors"] node_modules/debug/src/node.js:76:22
[PP][IsIn "colors"] node_modules/debug/src/node.js:76:22
[PP][IsIn "colors"] node_modules/debug/src/node.js:76:22
[PP][Prop noDeprecation] node_modules/depd/index.js:154:15
[...]
Example app listening on port 3000

Now, if you issue a request to that server, even more candidate show up:

[PP][Prop params] node_modules/express/lib/router/index.js:156:26
[PP][Prop baseUrl] node_modules/express/lib/router/index.js:157:23
[PP][Elem "baseUrl"] node_modules/express/lib/router/index.js:637:19
[PP][Elem "next"] node_modules/express/lib/router/index.js:637:19
[PP][Elem "params"] node_modules/express/lib/router/index.js:637:19
[...]

Commands

Hook

Add pp-finder hooks to a file or directory.

This will create a backup of each file in ~/.local/share/pp-finder

$ pp-finder hook --help                                                                                                                                                                              PP-Finder hook
> Instrument a javascript project

ARGUMENTS:
  <Path> - Path of the file or directory to instrument

OPTIONS:
  --name, -n <str> - Wrapper name, (default "ø") [optional]

FLAGS:
  --help, -h - show help

Hook a file or directory,

Restore

Restore the backup (if available) for a file or directory

PP-Finder restore
> Remove pp-finder hooks from a javascript file or directory

ARGUMENTS:
  <Path> - Path of the file or directory to restore

FLAGS:
  --help, -h - show help

Rehoook

This is moslty for developement purpose, restore and rehook a file / directory

Purge

Remove all backups

PP-Finder purge
> Purge all backups

ARGUMENTS:
  [path] - Path of the file or directory to remove from the backup [optional]

FLAGS:
  --help, -h - show help

Runtime Configuration

You can configure the behaviour of PP finder using env variable:

| Environment | Type | Description | | :--------------- | :-------------------------- | :----------------------------------------------------- | | PPF_CONFIG_PATH | string | Path to config file, defaults to ./ppf.config.json | | PPF_LOGONCE | bool | Only log each finding once, defaults to false | | PPF_COLOR | 'auto', 'always' or 'never' | Disable colorization, defaults to false | | PPF_WRAPPER_NAME | string | Wrapper name, defaults to ø | | PPF_POLLUTABLE | string[], comma separated | Pollutable objects, defaults to ["Object.prototype"] | | PPF_LOG_FORIN | bool | Log for (y in x) gadgets, defaults to true | | PPF_LOG_ISIN | bool | Log y in x gadgets, defaults to true | | PPF_LOG_PROP | bool | Log x.y gadgets, defaults to true | | PPF_LOG_ELEM | bool | Log x[y] gadgets, defaults to true | | PPF_LOG_BIND | bool | Log {y} = x gadgets, defaults to true |

Tests

Tests indicate what the library handles in terms of AST visitors:

$ yarn test
  Hooks
    PropertyAccessExpression
      ✔️ Valid Gadget     | ({}).y
      ✔️ Not Valid Gadget | ({y: 42}).y
      ✔️ Not Valid Gadget | (Object.create(null)).y
      ✔️ Valid Gadget     | ({y: {}}).y.z
    ElementAccessExpression
      ✔️ Valid Gadget     | ({})['y']
      ✔️ Not Valid Gadget | ({y: 42})['y']
      ✔️ Not Valid Gadget | (Object.create(null))['y']
      ✔️ Valid Gadget     | ({y: {}})['y']['z']
    ForInStatement
      ✔️ Valid Gadget     | for(let y in ({})){}
      ✔️ Not Valid Gadget | for(let y in (Object.create(null))){}
    ArrowFunctionDeclaration
      ✔️ Valid Gadget     | (({y}) => (0))({})
      ✔️ Valid Gadget     | (({y}, a, {z}) => (0))({}, 0, {})
      ✔️ Valid Gadget     | (({y: z}) => (0))({})
    FunctionDeclaration
      ✔️ Valid Gadget     | function f({y}){return};f({})
      ✔️ Valid Gadget     | function f({y}, a, {z}){return};f({}, 42, {})
      ✔️ Valid Gadget     | function f({y: z}){return};f({})
      ✔️ Valid Gadget     | function f({['y']: z}){return};f({})
    FunctionExpression
      ✔️ Valid Gadget     | (function ({y}){return})({})
      ✔️ Valid Gadget     | (function ({y}, a, {z}){return})({}, 0, {})
      ✔️ Valid Gadget     | (function ({y: z}){return})({})
      ✔️ Valid Gadget     | (function ({['y']: z}){return})({})
    InExpression
      ✔️ Valid Gadget     | ("y" in {})
      ✔️ Not Valid Gadget | ("y" in {y: 42})
      ✔️ Not Valid Gadget | ("y" in Object.create(null))
    ObjectLiteral
      ✔️ Valid Gadget     | ({y} = {});
      ✔️ Valid Gadget     | ({y: {z}} = {y: {}});
      ✔️ Not Valid Gadget | ({y} = {y: 42});
      ✔️ Not Valid Gadget | ({y} = Object.create(null));
      ✔️ Valid Gadget     | ({['y']: y} ={});
    VariableDeclaration
      ✔️ Valid Gadget     | const {y} = {};
      ✔️ Valid Gadget     | const {y} = {}, {z} = {};
      ✔️ Valid Gadget     | const {y: {z}} = {y: {}};
      ✔️ Not Valid Gadget | const {y} = {y: 42};
      ✔️ Valid Gadget     | const {['y']: y} ={};
      ✔️ Not Valid Gadget | const {y} = Object.create(null);
      ✔️ Valid Gadget     | let z; const {y} = {z} = {};

  Assignation check
    ✔️ const x = {}; x.y = 42; x.y
    ✔️ const x = {}; x['y'] = 42; x.y


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