CVE-2025-64718: Fix Js-yaml Prototype Pollution

Hey guys! Let's dive into a security issue that's been identified in one of our dependencies. Knowing about these things helps us keep our projects secure and our users safe. We're talking about CVE-2025-64718, a medium severity vulnerability found in js-yaml-3.14.1.tgz. This vulnerability falls under the category of prototype pollution, which can be a real headache if not addressed properly. So, let's break down what this means for your projects and how to tackle it.

Vulnerable Library: js-yaml-3.14.1.tgz

What is js-yaml?

For those unfamiliar, js-yaml is a JavaScript library used for parsing and serializing YAML (YAML Ain't Markup Language) data. YAML is a human-readable data serialization format commonly used for configuration files and in applications where data is being stored or transmitted. The js-yaml library makes it easy for JavaScript applications to work with YAML data by providing functions to convert YAML data into JavaScript objects and vice versa. It's a popular choice due to its simplicity and wide adoption in the JavaScript ecosystem.

The Vulnerability

The identified vulnerability lies within js-yaml version 3.14.1. Specifically, it's a prototype pollution issue. Prototype pollution occurs when an attacker can manipulate the __proto__ property of an object, leading to unintended modifications of the object's prototype. This can have widespread implications, potentially affecting all objects that inherit from the polluted prototype. This is a big deal because it can lead to all sorts of unexpected behavior and security risks. In the context of js-yaml, if an attacker can control the YAML input that is parsed by js-yaml, they can potentially inject malicious properties into the prototype of JavaScript objects, leading to code execution or other undesirable outcomes. It's like messing with the foundation of how objects work in JavaScript, which can cause chaos.

Impact

The impact of this vulnerability can range from denial-of-service to arbitrary code execution, depending on how the application utilizes the parsed YAML data. If an attacker successfully pollutes the prototype, they might be able to inject malicious code that gets executed when the application interacts with objects inheriting from the polluted prototype. This could potentially compromise the entire application and any sensitive data it handles. So, it's not just a minor issue; it can have serious consequences. In simpler terms, imagine someone sneaking into your house and changing the master blueprint. Now, every time you build something based on that blueprint, it has unexpected and potentially dangerous flaws.

Where is it Found?

This vulnerable library is found in the dependency hierarchy of eslint-7.32.0.tgz, a popular JavaScript linter. The path to the vulnerable library is /node_modules/js-yaml/package.json. It was detected in the HEAD commit da9164953160f02cde489a24633e8bb244a39be4 and is present in the base branch main of the mcaj-git/vidavidorra-repo-template repository. So, if your project uses eslint-7.32.0.tgz, it's likely that you're also using the vulnerable version of js-yaml. It's crucial to check your project's dependencies and take action to mitigate this vulnerability.

Vulnerability Details

Prototype Pollution

js-yaml versions 4.1.0 and below are susceptible to prototype pollution. An attacker can modify the prototype of the result of a parsed YAML document via the __proto__ property. This affects all users who parse untrusted YAML documents. Basically, if you're parsing YAML data from an untrusted source, you're at risk. Prototype pollution can lead to various security issues, including denial of service and potentially remote code execution. It's like giving an attacker the keys to the kingdom, allowing them to manipulate the behavior of your application in unexpected ways.

Mitigation

To protect against this kind of attack on the server, you can use node --disable-proto=delete or deno (in Deno, pollution protection is on by default). However, the best solution is to upgrade to a patched version of js-yaml that addresses this vulnerability. Disabling prototype modification can provide a layer of defense, but it's not a foolproof solution. Upgrading the library ensures that the vulnerability is properly fixed and that you're using a secure version of the code. Think of it as patching a hole in your wall versus just putting a piece of tape over it.

CVSS 3 Score Details (5.3)

Understanding the Score

The Common Vulnerability Scoring System (CVSS) provides a standardized way to assess the severity of security vulnerabilities. A CVSS score of 5.3 is considered a medium severity vulnerability. This score is derived from several factors, including the attack vector, complexity, privileges required, user interaction, scope, confidentiality impact, integrity impact, and availability impact. Understanding these metrics can help you prioritize the remediation efforts based on the potential risk to your application.

Base Score Metrics

The base score metrics for this vulnerability are as follows:

• Exploitability Metrics:
  • Attack Vector: Network
  • Attack Complexity: Low
  • Privileges Required: None
  • User Interaction: None
  • Scope: Unchanged
• Impact Metrics:
  • Confidentiality Impact: None
  • Integrity Impact: Low
  • Availability Impact: None

These metrics indicate that the vulnerability can be exploited over a network with low complexity and without requiring any privileges or user interaction. The impact on integrity is low, while there is no impact on confidentiality or availability. This means that while an attacker can modify data, they cannot access confidential information or disrupt the availability of the system. However, even a low impact on integrity can have significant consequences, especially if the modified data is critical to the functioning of the application.

Why This Matters

Even though the CVSS score is medium, it's important not to underestimate the potential impact of this vulnerability. Prototype pollution can be a subtle and difficult-to-detect issue that can lead to unexpected behavior and security risks. By understanding the CVSS score and the underlying metrics, you can make informed decisions about how to prioritize and address this vulnerability in your application. Don't let a medium score lull you into a false sense of security; take proactive steps to protect your application and data.

Suggested Fix

Upgrade Version

The recommended fix is to upgrade to js-yaml version 4.1.1 or later. This version includes a patch that addresses the prototype pollution vulnerability. Upgrading is the most effective way to mitigate the risk and ensure that your application is protected. It's like getting a vaccine to protect yourself from a disease; it's a proactive measure that can prevent serious problems down the road.

Origin

The fix originates from a security advisory on GitHub: https://github.com/nodeca/js-yaml/security/advisories/GHSA-mh29-5h37-fv8m. This advisory provides detailed information about the vulnerability and the steps taken to address it. It's a valuable resource for understanding the issue and ensuring that you're implementing the fix correctly.

Release Date

The release date of the fix is November 13, 2025. It's important to stay up-to-date with security releases and apply them as soon as possible to protect your application from known vulnerabilities. Think of it as keeping your antivirus software updated; you want to have the latest protection against emerging threats.

Fix Resolution

• js-yaml: Upgrade to version 4.1.1
• eslint: Upgrade to version 8.0.0 (as a direct dependency fix resolution)

Upgrading eslint to version 8.0.0 will also resolve the vulnerability, as it includes the updated version of js-yaml. This is a convenient way to address the issue if you're already planning to upgrade eslint. It's like killing two birds with one stone; you get the benefits of the new eslint version and the security fix for js-yaml.

Remember, keeping our dependencies updated is super important for maintaining a secure and reliable application. Stay safe out there!

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