agency-testtsnpm
Advisory published Updated
agency-testts is a confirmed malicious npm package (MAL-2026-17171) that executes malicious code on install (malicious version 1.0.0). Do not install it — remove it immediately and rotate any exposed credentials.
Malicious code in agency-testts (npm)
What this malware does
package.json declares a postinstall lifecycle hook wscript.exe 4444.vbs that auto-runs on npm install on Windows. The bundled 4444.vbs is a ~674KB script containing large opaque base64 blobs and an AES key/IV pair (stateFKK, manifestGCP) which it uses at runtime to decrypt an embedded payload via CreateDecryptor().TransformFinalBlock and hand it to C:\Windows\System32\WindowsPowerShell\v1.0\powershell.exe for execution. After staging, the script self-cleans with cmd.exe /c ping 127.0.0.1 -n 8 >nul & del /f /q... & rmdir /s /q... to remove its own artifacts. Cover-story comments label the script a Sync Agent — diagnostic telemetry collector from a fictitious Wingtip Toys Corporation, but the code performs no telemetry-shaped behavior — it decrypts and executes an opaque payload. The package ships no other functionality; installing it on Windows results in arbitrary attacker code running under the installer's user account.
Malicious versions
Indicators of compromise (SHA-256)
Detection & response playbook
Malicious packageFind it
Search your lockfiles and build artifacts for agency-testts (version 1.0.0).
If you installed it — respond
Remove agency-testts 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 agency-testts 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 agency-testts-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.