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The Claude Code Backdoor That Failed on a Permission Error
A tampered build sat in Cursor’s marketplace for eleven hours and reached as many as 5,000 developer machines.
For eleven hours and eight minutes on Thursday, “official” stopped meaning safe.
Between 09:27 and 20:35 UTC on 29 October, the Claude Code extension for VS Code inside Cursor’s marketplace carried an injected payload (The Register, 30 Oct). It ran the moment Node loaded extension.js, appended an attacker's Ed25519 key to ~/.ssh/authorized_keys, and opened a reverse SSH tunnel to 134.209.82[.]225 (Phorion, 30 Oct).
Cursor puts the reach at “at most 5,000 users” (Wired, 30 Oct). Extensions auto-update in Cursor by default, and users can turn that off in settings. Most don’t. Phorion CTO Luke Roberts, to Ars Technica: “Extensions auto-update in Cursor by default, but users can configure this in settings” (Ars Technica, 30 Oct).
The malware broke on macOS. It checked whether Remote Login was enabled by running systemsetup -getremotelogin without admin rights. The tool refuses, prints an error, and exits with status 0. The script read that error as "SSH is already on" and skipped the step that would have turned it on. On a Mac without Remote Login running, the tunnel dialed out and anything…
