# MAL-2026-5750: Malicious code in mailconfirmer (npm)


- **Type:** Malicious package
- **Package:** `mailconfirmer` (npm)
- **Published:** 13 Jun 2026
- **Also known as:** GHSA-4rw6-v77j-67gx

## What is MAL-2026-5750?

MAL-2026-5750 is a malicious package in mailconfirmer, published on 13 Jun 2026. 

### Official description

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.

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-2026-5750?

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-2026-5750 is a malicious package: mailconfirmer (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-2026-5750/ (Markdown: https://insights.sbomify.com/MAL-2026-5750/index.md)
```

## Sources

- OSV: https://osv.dev/vulnerability/MAL-2026-5750

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From sbomify Insights: https://insights.sbomify.com/MAL-2026-5750/
Summaries are generated and may contain mistakes; the official description above is the record.