New Flaw Exposes Visual Studio Code and Popular IDEs to Malicious Verified Extensions: What Every Developer Must Know

If you believe that the “verified” checkmark on your favorite IDE extensions means you’re immune from security surprises, it’s time for a reality check. Recent research from OX Security has exposed a worrying flaw in some of the world’s most popular integrated development environments (IDEs), including Visual Studio Code, Visual Studio, IntelliJ IDEA, and Cursor. This vulnerability lets malicious actors sneak harmful code into what appears to be trusted, verified extensions—putting developer machines, source code, and even production environments at risk.

So, what exactly is happening? How does this flaw work, and, more importantly, what should you do to protect yourself? Let’s break it all down in plain English—because when it comes to your development environment, there’s no room for mystery.

Understanding the Verified Extension Flaw in IDEs

First, let’s get our bearings. IDEs like Visual Studio Code, IntelliJ IDEA, and others have revolutionized how developers write, debug, and ship code. Part of this flexibility comes from their thriving extension ecosystems—plugins that add everything from Git integration and AI pair programming to custom themes and code linters.

Most of us rely on these extensions daily, and we’ve been taught to trust those sporting a “verified” badge or publisher icon. That badge is supposed to mean the extension underwent extra checks and came from a reputable source.

But what if someone could fake that trust?

The Flaw, Simplified

Here’s the crux: Researchers found that IDEs like Visual Studio Code, IntelliJ IDEA, and Cursor have flaws in their extension verification process. Specifically:

Attackers can craft malicious extensions that mimic the verification values of legitimate ones.
These rogue extensions keep the trusted “verified” status and icon—even though they contain dangerous code.
This gives attackers an easy way to trick developers into installing malware under the guise of a verified extension.

Why does this matter? Because developers often have access to sensitive credentials, secrets, and codebases. A malicious extension isn’t just a nuisance; it’s a direct pipeline for attackers into your most valuable assets.

How the Visual Studio Code Extension Verification Process Is Bypassed

Still with me? Let’s dive a little deeper. Here’s how the attack works—step by step, but without getting too technical:

Verification Status via HTTP: When Visual Studio Code checks if an extension is “verified,” it sends a POST request to its marketplace domain: marketplace.visualstudio[.]com.
Values Can Be Spoofed: The request includes data that identifies the extension. Researchers discovered that by copying or modifying certain values from a verified extension (like one published by Microsoft), you can craft a new, malicious extension that appears “verified.”
Dangerous Payload Hidden: The attacker can insert code that executes OS commands. For the proof of concept, OX Security simply opened the Calculator app on Windows to demonstrate this capability—but it could just as easily steal credentials, access private repos, or worse.
Extension Sideloading: The risk escalates when developers install extensions directly from VSIX files (the extension package format) instead of through the official marketplace.

What Makes This So Sneaky?

The “Verified” Badge Is Faked: Developers see the trusted icon and assume the extension is safe.
No Marketplace Publishing Needed: Since the extension can be sideloaded (i.e., installed from a file or external link like GitHub), it never even needs to pass through Microsoft’s stricter controls.
Works Across Multiple IDEs: The flaw isn’t limited to Visual Studio Code. It also affects other major platforms like IntelliJ IDEA and Cursor.

Here’s why that matters: If you install extensions from unofficial sources—even those that look “verified”—you’re at risk.

The Security Impact: Why Developers Can’t Ignore This

It’s tempting to think: “I only use extensions from big publishers,” or “I’m careful about what I install.” But this flaw undermines the very signals developers rely on to stay safe.

What’s at Stake?

Remote Code Execution (RCE): Malicious extensions can run arbitrary commands on your machine. That’s a nightmare scenario—especially considering the sensitive data and credentials many developers work with.
Supply Chain Attacks: Your development environment is often linked to staging and production systems. If an attacker gets in here, they can pivot to other systems or inject backdoors into the codebase.
False Sense of Security: The verified icon, which should mean “safe,” is now unreliable in certain installation scenarios.

Who’s Most at Risk?

Developers who install VSIX/ZIP extensions from GitHub, forums, or file shares.
Teams with lax policies around extension management.
Those using multiple IDEs, not just Visual Studio Code.

Real-World Example: Proof of Concept

OX Security’s researchers showcased the risk by creating a VSIX extension that looked verified but simply opened the Calculator app upon installation—a harmless demo, but a stand-in for far more dangerous payloads.

How Extension Sideloading Opens the Door to Attackers

Let’s pause and clarify: What is extension sideloading?

Sideloading means installing an extension by importing a local file (VSIX or ZIP) rather than downloading it through the official marketplace.

Why do developers sideload extensions? – To test custom plugins before publishing. – To use experimental features or private/internal tools. – To install extensions not yet available on the marketplace.

But here’s the danger: When you sideload, the marketplace’s built-in signature verification and publisher checks can be bypassed or spoofed, as this flaw demonstrates.

The Classic Supply Chain Trap

Supply chain attacks have been on the rise—think SolarWinds, Codecov, and others. This flaw essentially creates a new pathway for attackers to compromise the software supply chain, starting at the developer workstation.

Microsoft’s Response and the Industry’s Blind Spots

When OX Security responsibly disclosed the flaw, Microsoft responded that the behavior was “by design.” They clarified that extensions failing signature verification can’t be published to the official Marketplace.

That’s partially reassuring—but only if developers stick strictly to Marketplace installs. The flaw remains exploitable when sideloading extensions, which Microsoft (and other vendors) allow for flexibility and testing.

Other IDEs are affected, too. OX Security’s research showed that by tweaking the verification values, malicious actors could create verified-looking extensions for IntelliJ IDEA and Cursor.

Why “By Design” Is Not Always Enough

Security, like software, depends on real-world usage. If a feature or workflow (like sideloading) is open to abuse, it’s not enough to point to official processes. Developers need practical safeguards—because attackers always look for the path of least resistance.

What Developers and Teams Should Do Right Now

Now that we know the risk, let’s focus on concrete actions. Protecting your IDE environment doesn’t have to be complicated, but it does require vigilance.

1. Only Install Extensions From Official Marketplaces

Stick to the official Marketplace or Plugin Repositories for your IDE.
Avoid installing VSIX, ZIP, or other extension files from GitHub or third-party sites unless you fully trust—and have verified—the publisher and the code.

2. Review Extension Permissions and Source Code

Before installing any extension, check what permissions it requests and, if possible, review its source code.
For open-source extensions, look for active maintenance and community trust signals.

3. Educate Teams on Sideloading Risks

Share this information with your team. Many developers aren’t aware that sideloaded extensions can bypass key checks.
Establish clear extension management policies—ideally with an allowlist of trusted plugins.

4. Monitor for Unusual Extension Behavior

Watch for extensions that request excessive permissions or behave unexpectedly after installation.
Use OS-level security controls (like endpoint detection and response) to catch unusual activity.

5. Keep IDEs and Plugins Updated

Vendors frequently patch security loopholes. Make sure your IDE and all extensions receive regular updates.

Looking Ahead: The Future of Extension Security

This incident is a wake-up call—not just for developers, but for IDE vendors and the entire software supply chain. As plugin ecosystems grow, so does the attack surface. Security must evolve with it.

Here’s what needs to happen next:

Stronger Code Signing: IDEs should enforce signature checks even for sideloaded extensions, or at least warn users about the risks.
Improved User Warnings: Developers should see clear alerts when installing extensions from outside trusted sources.
Greater Transparency: Make it easier for users to audit extension provenance and publisher history.

Frequently Asked Questions (FAQ)

What is the Visual Studio Code “verified” extension flaw?

It’s a vulnerability that allows attackers to create malicious extensions for IDEs like Visual Studio Code, making them appear as verified/trusted even though they contain harmful code. This mainly affects developers who sideload extensions as VSIX files rather than installing from the official Marketplace.

How can I avoid installing a malicious extension?

Always install extensions from your IDE’s official marketplace.
Be wary of extensions distributed on GitHub or other sites, especially if they ask you to sideload a VSIX or ZIP file.

Does this flaw only affect Visual Studio Code?

No. OX Security found similar issues in other major IDEs, including IntelliJ IDEA and Cursor, by modifying how the verification values are set.

What is extension sideloading and why is it risky?

Sideloading is when you install an extension from a local file instead of the official marketplace. This bypasses many security checks, making it easier for malicious actors to distribute harmful plugins that look verified.

What is Microsoft doing to fix this?

Microsoft stated that its Marketplace enforces extension signature verification by default, so extensions with spoofed verification values can’t be published in the Marketplace. However, sideloaded extensions are still a risk, and Microsoft has not announced additional mitigations as of June 2025.

Should I uninstall all my current extensions?

No, but you should review your installed extensions for legitimacy—especially any that were installed outside of the Marketplace or from untrusted sources.

Where can I find more information about extension security?

For more details, see The Hacker News coverage, Microsoft’s Marketplace publishing documentation, and OX Security’s original research post.

The Bottom Line: Trust, But Verify—And Stay Vigilant

At the end of the day, the tools meant to make our lives easier can also open doors to attackers—especially when trust signals like the “verified” badge can be spoofed. As developers, it’s on us to stay informed, practice good security hygiene, and push vendors for better safeguards.

Here’s one actionable takeaway:
Always install extensions from official sources and educate your team about the hidden risks of sideloading. If you’re unsure about an extension’s provenance, err on the side of caution.

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Stay curious, stay safe, and happy coding!

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New Flaw Exposes Visual Studio Code and Popular IDEs to Malicious Verified Extensions: What Every Developer Must Know