Cursor takes marketplace offline after malicious extension targets 5,000 users

Cursor temporarily disabled its entire VS Code extension marketplace on Thursday after discovering a tampered version of the Claude Code extension, according to The Decoder.reported The company stated that the malicious package was available for about eleven hours and may have affected up to 5,000 users.reported Anthropic confirmed it had no involvement in the development or distribution of this specific compromised extension.

What it does

The tampered extension attempted to harvest specific system information from infected machines, including hostname, username, operating system details, and public IP addresses. It also tried to establish remote access channels for the attacker. Cursor noted that the remote access component likely failed on most systems because it required administrative privileges to execute successfully.

How to get it

The compromised software was distributed through Cursor’s official VS Code extension marketplace. Users who installed the extension during the eleven-hour window when it was live were exposed to the threat. Cursor subsequently removed the specific extension and took the entire marketplace offline to ensure no other compromised packages remained.

Limits

The attack’s effectiveness was constrained by system permissions. Cursor reported that the remote access attempt likely would not have worked on most machines due to the requirement for admin privileges.reported Additionally, the exposure window was limited to approximately eleven hours before the company detected the anomaly and initiated mitigation procedures.

The takeaway

Cursor worked with external providers to neutralize the malware and confirmed there was no further risk before reinstating the marketplace. The company stated that no other extensions were affected by this incident. This event highlights the potential for supply chain attacks within developer tool ecosystems, even when using official distribution channels.

Building on this

Data science teams should audit their extension installations, particularly those granting system-level access, to ensure they originate from verified publishers. Since the malicious extension attempted to collect hostnames and IP addresses, organizations should monitor for unauthorized outbound connections from development environments. Teams should verify that extensions like Claude Code are sourced directly from Anthropic or authorized distributors, as third-party tampering can occur even in curated marketplaces.