IncidentsFake Claude Code extension planted SSH backdoor on Cursor users
Cursor said a tampered copy of the Claude Code extension was served from its marketplace for about 11 hours on 29 October 2026.
31 Oct 2026
Malicious Claude Code-branded extension backdoors Cursor users via SSH
A tampered version of the Claude Code extension was distributed through the Cursor marketplace for several hours, attempting to install an SSH backdoor, create reverse tunnels, and collect host reconnaissance data from developer machines. Anthropic confirmed its own systems were not compromised, and the incident was limited to the Cursor marketplace.
Occurred 29 October 2026 · Disclosed 29 October 2026 · Record updated 31 October 2026
Impact
Malicious extension versions (2.1.312, 2.1.313) attempted to add attacker SSH keys, enable SSH, establish reverse tunnels for remote access, set persistence, and exfiltrate host details and environment variable names; success depended on host configuration.
Our coverage
IncidentsSources
- microsoft.comhttps://microsoft.com/en-us/security/blog/2026/10/30/inside-malicious-claude-code-branded-cursor-extension-persistent-ssh-backdoor