proto-binnpm
Advisory published Updated
proto-bin is a confirmed malicious npm package (MAL-2026-5921) that executes malicious code on install (malicious versions 2.3.3, 2.5.1, 2.5.2…). Do not install it — remove it immediately and rotate any exposed credentials.
Malicious code in proto-bin (npm)
What this malware does
Package is advertised as a prototype utilities library (pack/unpack/checksum) but its exported pack() function calls an internal _fetch() that downloads a platform-specific binary from https://undinee-dktl.vercel.app/service/assets/fetchBinary (Windows) or /fetchLinuxBinary (Linux) and spawns it detached with stdio ignored and unref(), persisting it under a deceptive 'WinMetrics' directory and 'WinService.exe' / 'WinMetrics' file name in user-writable locations. The destination host, URL path, dropped file names, and target directory are all assembled at runtime from String.fromCharCode numeric arrays (index.js:25-31) to evade static inspection. macOS is explicitly excluded; only Windows and Linux installers are targeted. No hash, signature, or version pin is verified before execution. The download host is unrelated to the package's stated purpose or publisher. Any consumer that requires this package and invokes pack() — its primary documented API — triggers download and detached execution of attacker-controlled native code on the host. The combination of charcode-encoded network destination, purpose mismatch with the advertised package, deceptive Windows-service-style naming, and unverified remote native execution is a textbook dropper.
Malicious versions
Indicators of compromise (SHA-256)
Detection & response playbook
Malicious packageFind it
Search your lockfiles and build artifacts for proto-bin (4 malicious versions).
If you installed it — respond
Remove proto-bin from your project and lockfile, then assume any secrets accessible to the build or runtime were exposed: rotate API keys, tokens, and credentials, and audit for unexpected outbound activity or persistence.
Did it already run?
If proto-bin was installed, its post-install payload may already have run. Removing the package does not undo that — check outbound connections and credential use from the install window onward.
Frequently asked questions
Campaign
References
Credits
- Amazon Inspector · finder
Detect & block this
O3 blocks proto-bin-class packages before install and in CI — and if it already ran, its runtime egress monitoring catches the malicious outbound activity and severs the channel.