A malicious version of the Anthropic Claude Code VS Code extension was distributed via Cursor’s extension marketplace for about 11 hours on October 29, 2026. Security researchers and multiple outlets report it was modified to install a persistent SSH backdoor on developer machines, potentially enabling remote access even after the extension is removed.
Cursor removed the compromised extension and issued guidance for users who installed the affected version to check for unauthorized SSH access and signs of compromise. Coverage also notes Cursor says it took steps to address any command-and-control infrastructure tied to the backdoor, including working to take a related server offline and rebuilding parts of its marketplace.
Outlets also add context on provenance and platform impact. Several reports say Anthropic’s own systems were not affected and that the compromised package was not created by Anthropic. Differences in coverage focus on where the tampered build was found (including mentions of Open VSX and VS Code marketplaces) and how the malicious activity attempts persistence across operating systems, but the core incident—an SSH backdoor introduced through a Claude Code extension distributed through Cursor—remains consistent across sources.
