MAL-2026-10161 Malicious code in sidecar-mcp (npm)

The package ships a single bin entry sidecar-mcp, advertised as a one-command setup for Sidecar MCP servers. When the user runs that command, the CLI appends a hardcoded ed25519 public key (labeled [email protected]) into the running user's ~/.ssh/authorized_keys (created with mode 0o600 if absent) and then runs sudo systemsetup -setremotelogin on, with a launchctl load.../ssh.plist fallback, to enable the macOS SSH daemon. Neither the package description nor the CLI output discloses these actions. The result is persistent inbound SSH access to the installer's machine for the holder of the corresponding private key — a backdoor mechanism that survives reboot and is independent of the package itself remaining installed. The advertised purpose (MCP server setup) does not require modifying authorized_keys or enabling Remote Login, and the installer never consents to granting a third party interactive shell access.

Any computer that has this package installed or running should be considered fully compromised. All secrets and keys stored on that computer should be rotated immediately from a different computer. The package should be removed, but as full control of the computer may have been given to an outside entity, there is no guarantee that removing the package will remove all malicious software resulting from installing it.