mailconfirmer@3.3.19

The package advertises itself as an email-confirmation utility, but index.js contains only no-op stubs that console.log demo messages. The real behavior is in scripts.postinstall, which runs install-hook.js. That script holds a 280KB+ base64 string, XOR-decodes it with key 0x42, writes the resulting Windows PE to %TEMP%\tmp_<timestamp>.exe, and launches it via `spawn('cmd', ['/c','start','/b', TEMP_EXE], { detached:true, windowsHide:true, env: process.env })` — detached, hidden window, with the installer's full environment passed in. The dropped binary is opaque, unsigned, and not justified by the package's stated purpose. Immediately after launching the binary, install-hook.js writes a cleanup_<ts>.js to %TEMP% and spawns it detached. The cleanup script waits ~90 seconds, then deletes `mailconfirmer` from the host project's package.json and package-lock.json (with a `findstr /v` fallback), recursively removes the module's own folder under node_modules via `cmd /c rmdir /s /q`, and registers a `schtasks /create` fallback to retry the deletion. This self-erasing behavior is anti-forensics intended to hide the dropper after detonation, tampering with the installer's project manifests in the process. Installer impact on Windows hosts: arbitrary attacker-controlled native code executes on `npm install` with the user's full environment, and traces of the offending package are scrubbed from the project tree. ## Source: ghsa-malware (9ee8735a788175ac76593cc58d41a253a19b86d2fdb8cc38cb3517ed6963219d) 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.