Winter CMS is a popular, free, open-source content management system (CMS) built on the Laravel PHP framework. It’s flexible, widely used, and well-regarded for its developer-friendly approach. But like all software, it’s not immune to security flaws.

In late 2022, a major security vulnerability known as CVE-2022-39357 was discovered in the "Snowboard" JavaScript framework bundled with certain versions of Winter CMS. If you use Winter CMS, understanding this flaw, how it works, and how to fix it, is vital.

This article will break down CVE-2022-39357 in simple language, include real code snippets, direct you to official advisories, and show you how the exploit works, plus how to stay secure.

What is CVE-2022-39357?

CVE-2022-39357 is a “prototype pollution” vulnerability found in the JavaScript code of the Snowboard framework, included by default in Winter CMS versions 1.1.8, 1.1.9, and 1.2..

Fixed patches: v1.1.10 and v1.2.1.

Reference:  
GitHub Security Advisory  
NVD CVE Page

What is Prototype Pollution?

Prototype pollution is a serious bug affecting JavaScript apps. In simple terms, attackers can manipulate the “prototype” of basic objects (like {}), which can change how your app behaves everywhere. For example:

How Does CVE-2022-39357 Work?

The issue is in how Snowboard copies objects and merges options, allowing attackers to sneak in “magical” property keys like __proto__.

Insecure Sample code (simplified version for illustration)

// bad object merging - vulnerable to prototype pollution
function mergeObjects(target, source) {
  for (let key in source) {
    target[key] = source[key];
  }
  return target;
}

let opts = {};
mergeObjects(opts, JSON.parse('{"__proto__": {"isHacked": true}}'));

console.log({}.isHacked); // true (!!!)

This code seems harmless. But if an attacker sends a payload like {"__proto__": {"isHacked": true}}, ALL JavaScript objects now have isHacked: true. This could lead to code execution or bypassing app logic.

The main Snowboard class and its plugin loader both merged user inputs directly.

- No protection was present against dangerous properties like constructor, __proto__, or prototype.
- By exploiting this, attackers could inject arbitrary properties into the global JavaScript object space.

Impact

- Remote Exploitation: Attackers only need to inject a crafted JSON object (e.g. via URL, AJAX, or POST body).
- Privilege Escalation: If your application relies on object properties for access control or logic, attackers can tamper with it.
- Further Exploits: In some cases, this can be escalated to Remote Code Execution (RCE), though that depends on your app code.

> Note: The actual exploitability depends on your frontend code. Snowboard by default is vulnerable, but attacks require a suitable injection point.

Exploitation Example

Here's a minimal demonstration of exploitation, assuming you have an app using the Snowboard framework (or a similar vulnerable merge function):

// Malicious payload sent to the app
const maliciousPayload = '{"__proto__": {"polluted": "pwned"}}';

function vulnerableMerge(obj, payload) {
  for(let key in payload) {
    obj[key] = payload[key];
  }
}

let userObj = {};
vulnerableMerge(userObj, JSON.parse(maliciousPayload));

if ({}.polluted === "pwned") {
  console.log("!!! Prototype polluted. Your app is at risk.");
}

After running this code, EVERY object’s polluted property is "pwned". Now, imagine that some part of your app checks if user.isAdmin is set, and attackers inject isAdmin: true via prototype pollution.

Snowboard v1.2.1

You should upgrade immediately to one of these versions if you’re affected.

Changelog / Patch:  
Winter CMS Changelog

Replace unsafe merges with ones that ignore dangerous keys

function safeMerge(target, source) {
  const dangerousKeys = ["__proto__", "prototype", "constructor"];
  for (let key in source) {
    if (dangerousKeys.includes(key)) continue;
    target[key] = source[key];
  }
  return target;
}

Limit script execution on your site. Set HTTP response headers

Content-Security-Policy: default-src 'self'; script-src 'self'

3. Script Auditing

Regularly check all third-party or custom JavaScript for unsafe code patterns like {...userInput} or Object.assign({}, userInput).

#### 4. Remove/Disable Snowboard

If you don't use Snowboard features, consider disabling or removing it temporarily.

Summary Table

| Version      | Vulnerable?   | Fixed?    |
|--------------|---------------|-----------|
| 1..x        | No            | -         |
| 1.1.8, 1.1.9 | Yes           | No        |
| 1.1.10+      | No            | Yes       |
| 1.2.        | Yes           | No        |
| 1.2.1+       | No            | Yes       |

If you run Winter CMS on public servers, update now.

- Audit your code for prototype pollution vulnerabilities, especially if you merge user-supplied objects.
- Use secure coding patterns for object merges in JavaScript, never blindly copying user input into global objects.
- Stay updated on new releases by following Winter CMS GitHub.

References

- Official Winter CMS Security Advisory
- NVD CVE-2022-39357
- Prototype Pollution Explained – Blog

Stay safe, keep your CMS updated, and don’t let prototype pollution snowball into a bigger problem!

Timeline

Published on: 10/26/2022 15:15:00 UTC
Last modified on: 10/28/2022 19:37:00 UTC