Open VSX, the open-source extension marketplace for Visual Studio Code, removed 77 malicious extensions that impersonated legitimate developer tools and exfiltrated system and environment data from infected machines.

Manifold Security discovered the "evil twin" campaign between July 26 and August 1, 2026. The extensions mimicked popular legitimate tools, a technique designed to bypass user scrutiny during installation. Once installed, the malicious packages transmitted information about the host systems and development environments to attacker-controlled servers.

The extensions targeted developers across multiple skill levels. By spoofing trusted tool names, attackers increased the likelihood of installation. Developers often install extensions to extend IDE functionality, creating an attack surface when malicious packages masquerade as legitimate alternatives.

The exfiltrated data included system configuration details, environment variables, and development setup information. This reconnaissance data allows attackers to map developer infrastructure, identify technology stacks, and locate potential entry points for follow-on attacks. For organizations, compromised developer machines represent a direct path to source code repositories, internal systems, and CI/CD pipelines.

Open VSX administrators removed all 77 packages from the marketplace following Manifold Security's disclosure. The timeline suggests a coordinated upload campaign rather than sporadic submissions. The malware authors likely created multiple fake identities to distribute the extensions simultaneously, a tactic that complicates detection by distributing malicious uploads across different accounts.

Developers using Open VSX should audit their installed extensions and verify that each tool matches its official publisher. The marketplace implements review processes, but human oversight cannot catch every threat. For organizations, implementing extension allowlists within VSCode configurations restricts developers to pre-approved packages. Regular security training on extension verification and installation procedures reduces the attack surface further.

This campaign demonstrates how supply chain attacks against developer tools remain effective. Open VSX serves developers globally, making it an