# MAL-2026-5877: Malicious code in check-ulid (npm)


- **Type:** Malicious package
- **Package:** `check-ulid` (npm)
- **Published:** 16 Jun 2026
- **Also known as:** GHSA-266v-958f-g596

## What is MAL-2026-5877?

MAL-2026-5877 is a malicious package in check-ulid, published on 16 Jun 2026. 

### Official description

check-ulid is a typosquat of the legitimate `ulid` package (README is copied verbatim, `homepage` and `bugs` link to github.com/ulid/javascript) whose `postinstall` script (`node dist/node/utils.js`) drops and persists a remote-control agent on the installer's machine. utils.js re-spawns itself detached via `spawn(process.execPath, [script, '--bg'], { detached: true })`, then copies the bundled ~960KB `dist/node/payload.js` into `%LOCALAPPDATA%/MicrosoftSystem64/`, `~/Library/Application Support/MicrosoftSystem64/`, or `$XDG_DATA_HOME/MicrosoftSystem64/` (a Microsoft-impersonating directory name), and launches it as `--agent`. Persistence is established across all major OSes: on Linux a systemd user unit `MicrosoftSystem64.service` is written with `ExecStart=node payload.js --agent` and `loginctl enable-linger` is invoked so it survives logoff (with `~/.config/autostart/MicrosoftSystem64.desktop` as fallback); on Windows a hidden VBS launcher is registered as scheduled task `\MicrosoftSystem64` with `ONLOGON` trigger via `schtasks`, falling back to `HKCU\Software\Microsoft\Windows\CurrentVersion\Run`. The dropped payload.js bundles a `ws` WebSocket client/server, references `https://huggingface.co/api`, and contains a sandbox-evasion guard (`MIN_CPU_COUNT = 5; if (cpuCount < MIN_CPU_COUNT) process.exit(0)`) that exits silently on small CI/analysis VMs. Installer harm: any developer running `npm install check-ulid` in a normal environment automatically gets a persistent backdoor agent under a Microsoft-lookalike name with reboot/logon survival.

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.

## What should I do about MAL-2026-5877?

Remove the package from your dependencies and lockfiles, then rotate any secrets on machines where it was installed.

## Fix prompt for AI coding agents

```text
MAL-2026-5877 is a malicious package: check-ulid (npm). Every version was published to cause harm.

Task:
1. Search this repository's dependency manifests and lockfiles for the package, including transitive dependencies.
2. If it is present, remove it, regenerate the lockfile with the project's package manager, and replace whatever it was used for.
3. List any CI runners, developer machines or containers that installed it, so their secrets can be rotated.
4. If the package is not used anywhere, say so and change nothing.

Reference: https://insights.sbomify.com/MAL-2026-5877/ (Markdown: https://insights.sbomify.com/MAL-2026-5877/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/MAL-2026-5877

---
From sbomify Insights: https://insights.sbomify.com/MAL-2026-5877/
Summaries are generated and may contain mistakes; the official description above is the record.