Critical VS Code Extensions Vulnerabilities Hit 125 Million Installs

Four popular VS Code extensions expose developers to file theft and remote code execution. Live Server, Code Runner, Markdown Preview Enhanced, and Microsoft Live Preview together have over 125 million installs. Attackers need just one flaw to compromise machines and move laterally.

OX Security researchers found these critical issues. A single malicious extension or vuln lets hackers steal local files and run code. Developers often run localhost servers and open shared repos without checks.

Live Server (CVE-2025-65717, CVSS 9.1) leaks files when developers visit rigged sites. JavaScript scans localhost:5500 and sends data to attackers. Still unpatched.

Markdown Preview Enhanced (CVE-2025-65716, CVSS 8.8) runs arbitrary JavaScript from crafted .md files. Port scanning and data exfil follow. Unpatched.

Vulnerability Breakdown

Each flaw creates different attack paths.

Extension	CVE ID	CVSS Score	Attack Vector	Status
Live Server	CVE-2025-65717	9.1	Malicious website + localhost scan	Unpatched
Markdown Preview Enhanced	CVE-2025-65716	8.8	Crafted .md file JavaScript	Unpatched
Code Runner	CVE-2025-65715	7.8	settings.json phishing	Unpatched
Microsoft Live Preview	None	N/A	Malicious site localhost access	Fixed v0.4.16

Code Runner needs social engineering to edit settings.json. Still executes arbitrary commands.

Microsoft patched Live Preview silently in September 2025 version 0.4.16.

Attack Scenarios

Developers face realistic compromise chains.

Hackers share git repos with booby-trapped markdown. Preview runs JS payload scanning internal ports. Localhost servers leak source code, API keys, configs.

Phishing tricks users into settings.json changes. Code Runner executes payloads from untrusted sources.

Impact Scope

125 million installs mean massive exposure.

• 10M+ Live Server: Default dev server for frontend work
• 50M+ Code Runner: Executes any code snippet instantly
• 40M+ Markdown Preview: Standard for documentation
• 25M+ Live Preview: Microsoft’s own preview tool

Enterprise dev teams run these on corporate laptops. One click compromises VPN access, internal tools.

Immediate Actions

Security teams must act now.

• Audit Extensions: Remove all four immediately
• Firewall Localhost: Block inbound localhost:5500, 3000 ports
• Review settings.json: Check for injected “code-runner.executorMap”
• Extension Policies: Whitelist only approved extensions
• Developer Training: Never open untrusted markdown or git repos

Enterprise Risk

VS Code dominates developer environments. Extension ecosystem lacks supply chain security.

Malicious extensions execute with full user privileges. No sandboxing. Direct filesystem and network access.

Organizations must treat IDE extensions as hostile code until proven safe.

Official Vendor Statements

OX Security: “One malicious extension compromises entire organizations through developer workstations.”

Protection Checklist

• Disable non-essential extensions completely
• Never run localhost servers during corporate VPN sessions
• Block all extension network access via firewall
• Audit git repo sources before cloning
• Deploy VS Code extension signing enforcement
• Monitor for localhost:5500-5502 traffic

FAQ