{"answers":{"affected":"1 open source package ship an affected version, including check-ulid.","exploited":"There is no known exploitation of MAL-2026-5877 in the wild and no public exploit code.","fix":"Remove the package from your dependencies and lockfiles, then rotate any secrets on machines where it was installed.","what":"MAL-2026-5877 is a malicious package in check-ulid, published on 16 Jun 2026."},"fix_prompt":"MAL-2026-5877 is a malicious package: check-ulid (npm). Every version was published to cause harm.\n\nTask:\n1. Search this repository's dependency manifests and lockfiles for the package, including transitive dependencies.\n2. If it is present, remove it, regenerate the lockfile with the project's package manager, and replace whatever it was used for.\n3. List any CI runners, developer machines or containers that installed it, so their secrets can be rotated.\n4. If the package is not used anywhere, say so and change nothing.\n\nReference: https://insights.sbomify.com/MAL-2026-5877/ (Markdown: https://insights.sbomify.com/MAL-2026-5877/index.md)","id":"MAL-2026-5877","markdown":"https://insights.sbomify.com/MAL-2026-5877/index.md","name":"MAL-2026-5877","record":{"aliases":["GHSA-266v-958f-g596"],"analysis":null,"analysis_generated_by":null,"assigner":null,"cpe":[],"cvss":{"score":null,"severity":null,"source":null,"vector":null,"version":null},"cwes":[],"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 \u003c 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.\n\nAny 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.","ecosystems":["npm"],"exploits":{"exploitdb":null,"first_seen":null,"github_poc":null,"max_poc_stars":null,"metasploit":null,"nuclei":null,"refs":[],"tier":null},"has_fix":false,"headline":"Malicious code in check-ulid (npm)","id":"MAL-2026-5877","indexable":true,"kev":null,"kind":"malicious","links":{"ecosystem":"npm","product":null,"products":[],"type":null,"year":"2026"},"n_packages":1,"n_references":null,"packages":[{"ecosystem":"npm","fixed":[],"introduced":["0"],"last_affected":[],"package":"check-ulid","purl":"pkg:npm/check-ulid","source":"MAL-2026-5877"}],"products":null,"published":"2026-06-16","related":[],"sources":[{"class":"attribution","licence":"Apache-2.0","name":"OpenSSF Malicious Packages","prefix":"MAL"}],"ssvc":{"automatable":null,"exploitation":null,"technical_impact":null},"state":null,"updated":null,"vendors":null},"summary":null,"url":"https://insights.sbomify.com/MAL-2026-5877/"}