New VS Code Zero-Day Lets Attackers Access Private GitHub Repositories

A security researcher has publicly disclosed a new Visual Studio Code zero-day vulnerability that can reportedly let attackers steal GitHub authentication tokens through github.dev. Microsoft has not released a patch yet, and the flaw currently has no assigned CVE identifier.

The vulnerability affects github.dev, the browser-based version of Visual Studio Code that lets users browse and edit GitHub repositories directly from a web browser. According to the disclosure, attackers can abuse VS Code’s sandboxed webview messaging system to install a malicious extension capable of extracting GitHub OAuth tokens.

The issue was disclosed by security researcher Ammar Askar, who also published proof-of-concept details demonstrating how the attack works.

How the VS Code Attack Works

The attack begins when a victim clicks a specially crafted malicious link. Once opened, the exploit abuses communication between sandboxed webviews inside github.dev.

The exploit can reportedly trigger the installation of a malicious extension inside the browser-based VS Code environment. That extension can then extract GitHub OAuth authentication tokens tied to the victim’s session.

According to Askar, the stolen token is not limited to only the repository opened in github.dev.

The researcher claims the token may provide access to every private GitHub repository the victim can access. The proof-of-concept reportedly demonstrates this by querying the GitHub API and listing private repositories connected to the compromised account.

Microsoft Has Not Released a Patch Yet

The vulnerability remains unpatched at the time of writing. Microsoft has not publicly commented on the disclosure, and the flaw does not currently appear to have a CVE ID assigned.

The lack of a patch means users may need to rely on temporary mitigations until Microsoft responds.

Temporary Mitigation for github.dev Users

Askar recommends clearing cookies and local site data for github.dev as a temporary mitigation step.

After clearing the stored data, users should see a new warning prompt asking whether the GitHub Repositories extension can sign in with GitHub.

This additional prompt can help users spot suspicious authentication requests or unexpected extension behavior.

Users working with sensitive repositories may also want to avoid opening untrusted github.dev links until Microsoft releases a fix.

Disclosure Sparks More Criticism of MSRC

The disclosure also reignited criticism surrounding Microsoft’s security response process.

Askar said he informed GitHub only one hour before publicly releasing details of the flaw. He claimed the fast disclosure was intentional because of previous negative experiences with Microsoft’s security handling process.

According to the researcher, Microsoft previously fixed another VS Code issue without acknowledging its security impact or properly crediting the discovery.

The incident follows recent criticism aimed at the Microsoft Security Response Center (MSRC) from another researcher known as Nightmare Eclipse. The researcher publicly disclosed multiple Windows zero-days earlier this year and later claimed GitHub banned his account.

Security Researchers Continue Raising Concerns

The VS Code zero-day arrives during a busy period for Microsoft-related security incidents.

Recently, security researchers warned that attackers started exploiting the Windows Netlogon vulnerability CVE-2026-41089 in the wild. Separately, password manager provider Dashlane was hit by brute-force attack as users reported account lockouts.

Developers and organizations using GitHub services may want to monitor Microsoft and GitHub security advisories closely until an official fix becomes available.

Via BleepingComputer