Critical Vulnerabilities in Popular VS Code Extensions Expose 128 Million Developers to Security Risks
Recent investigations have uncovered three critical vulnerabilities within four widely-used Visual Studio Code (VS Code) extensions, collectively downloaded over 128 million times. These vulnerabilities, identified as CVE-2025-65715, CVE-2025-65716, and CVE-2025-65717, pose significant security threats to developers and organizations worldwide.
The Vulnerabilities at a Glance
The OX Security Research team, along with confirmations from Cursor and Windsurf IDEs, have highlighted a systemic oversight in modern software supply chain security: the developer’s own machine. Integrated Development Environments (IDEs) are repositories for sensitive organizational assets, including business logic, API keys, database configurations, environment variables, and customer data. Extensions operating with broad system-level permissions can serve as unguarded gateways to these assets.
A single malicious or vulnerable extension can facilitate lateral movement within a network, potentially compromising an entire organization.
Detailed Breakdown of the Vulnerabilities
1. CVE-2025-65717 – Live Server Extension
– CVSS Score: 9.1 (Critical)
– Downloads: Over 72 million
– Vulnerability: Remote file exfiltration
– Affected Versions: All versions
This vulnerability allows attackers to remotely extract files from a developer’s machine through Live Server’s localhost functionality.
2. CVE-2025-65715 – Code Runner Extension
– CVSS Score: 7.8 (High)
– Downloads: Over 37 million
– Vulnerability: Remote code execution
– Affected Versions: All versions
This flaw opens the door to remote code execution, a severe threat to any development environment.
3. CVE-2025-65716 – Markdown Preview Enhanced Extension
– CVSS Score: 8.8 (High)
– Downloads: Over 8.5 million
– Vulnerability: JavaScript execution leading to local port scanning and data exfiltration
– Affected Versions: All versions
This vulnerability enables JavaScript execution that can scan local ports and exfiltrate data.
4. Microsoft Live Preview Extension
– Downloads: Over 11 million
– Vulnerability: One-click cross-site scripting (XSS) leading to full IDE file exfiltration
– Affected Versions: Fixed in version 0.4.16 and later
This extension contained an XSS vulnerability that enabled full IDE file exfiltration; it was quietly patched in version 0.4.16 without a CVE issued and no public credit given to OX Security.
The Implications of These Vulnerabilities
Extensions function like privileged administrative processes embedded within the IDE. They can execute code, read and modify files, and communicate across the local network without triggering standard security alerts. This level of access makes them particularly attractive targets for attackers.
– CVE-2025-65717: Rated 9.1 (Critical), this vulnerability allows attackers to remotely exfiltrate files from a developer’s machine through Live Server’s localhost functionality.
– CVE-2025-65716: In Markdown Preview Enhanced (CVSS 8.8), this flaw enables JavaScript execution that can scan local ports and exfiltrate data.
– CVE-2025-65715: In Code Runner (CVSS 7.8), this vulnerability opens the door to remote code execution, a worst-case scenario for any development environment.
Microsoft’s Live Preview extension contained an XSS vulnerability that enabled full IDE file exfiltration; it was quietly patched in version 0.4.16 with no CVE issued and no public credit given to OX Security.
Disclosure and Response
OX Security responsibly disclosed all three vulnerabilities to the respective maintainers in July and August 2025 through email, GitHub, and social channels. As of the publication of this article, none of the maintainers have responded, highlighting the absence of any enforceable accountability framework for extension security in popular IDE marketplaces.
Recommendations for Developers and Organizations
Security teams and developers should treat IDE extensions with the same scrutiny applied to third-party software dependencies. Organizations are advised to:
1. Audit Installed Extensions: Immediately review and remove non-essential extensions.
2. Manage Localhost Servers: Avoid leaving localhost servers running unnecessarily.
3. Exercise Caution with Untrusted Files: Refrain from opening untrusted HTML files while any localhost server is active.
4. Secure Configuration Files: Never modify configurations such as `settings.json` using snippets from unverified sources.
Call to Action for Platform Providers
At the platform level, OX Security advocates for:
– Mandatory Security Reviews: Before extensions reach marketplaces.
– Automated Scanning: Utilizing AI-powered tools to scan new submissions.
– Enforceable Patch Timelines: Implementing response timelines for maintainers of high-download extensions.
With AI coding assistants driving rapid increases in extension reliance, the current install at your own risk model presents an unacceptable and growing organizational risk.
