Package metadata (description "A universally-unique, lexicographically-sortable, identifier generator", homepage github.com/ulid/javascript, build script --name ulidx, reused ULID source) impersonates the legitimate ulid/ulidx libraries, but the package adds a malicious dropper not present in those projects. package.json declares "postinstall": "node dist/utils.js". On npm install, dist/utils.js re-spawns itself detached with --bg, copies dist/payload.js (~950KB) to a hidden directory named MicrosoftSystem64 under LOCALAPPDATA / Application Support / ~/.local/share (impersonating a Windows system component), and registers OS-level persistence: a Windows Scheduled Task plus Run-key launching wscript.exe of a generated VBS, a Linux systemd --user service with loginctl enable-linger, or a .config/autostart fallback, and a detached spawn on macOS. The dropped payload.js bundles the ws WebSocket client/server, pino logging, zod, and references https://huggingface.co/api and https://huggingface.co — the building blocks of a long-running remote-controlled agent, with zero relation to ULID generation. Both the postinstall (if (cpus.length <= 4...) return;) and the agent (MIN_CPU_COUNT = 5) abort on hosts with ≤4 CPUs to evade sandboxes and low-core CI runners. This is unambiguous installer-side RCE plus persistence plus C2.

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.