Backdoor discovered in Claude code for VS extension on Cursor Marketplace
anthropic claude cursor
| Source: HN | Original article
A trojanized Claude Code extension on the Cursor Marketplace was found to contain a backdoor, exposing VS Code users to potential security risks.
A trojanized build of Anthropic’s Claude Code extension for Visual Studio Code was briefly distributed through the Cursor Marketplace, exposing thousands of developers to a persistent SSH backdoor. The malicious package, identified as version 2.1.313, appeared as a legitimate update on October 29 and remained available for roughly 11 hours before being withdrawn. Security researchers estimate that as many as 5,000 users may have installed the compromised extension, which silently planted an SSH key and opened a reverse tunnel to an attacker‑controlled server.
The incident follows a series of supply‑chain compromises reported earlier this week, including backdoors found in official Claude Code extensions hosted on other platforms. As we reported on 30 October, those earlier findings already raised concerns about the integrity of Anthropic’s tooling. This new vector demonstrates how attackers can exploit trusted marketplaces to reach a broad developer audience, turning everyday coding environments into footholds for lateral movement inside corporate networks.
The ramifications extend beyond the immediate risk of unauthorized system access. A compromised development workstation can leak proprietary code, credentials, and build artifacts, undermining both intellectual property protection and DevSecOps pipelines. The episode also highlights the limited visibility developers have into the provenance of extensions and the need for stricter vetting by marketplace operators.
Going forward, observers will watch for an official response from Anthropic and Cursor, including any patches, revocation of the tainted version, and steps to improve extension signing and distribution controls. Security teams are advised to audit installed extensions, rotate SSH keys, and monitor for anomalous outbound connections. The broader community is likely to push for tighter supply‑chain safeguards across VS Code marketplaces to prevent a repeat of this episode.
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