Fast file‑upload malware scanning for Node.js — optional YARA integration, ZIP deep‑inspection, and drop‑in adapters for Express, Koa, and Next.js. Private by design. Typed. Tiny.

Keywords: file upload security · malware detection · YARA · Node.js middleware · Express · Koa · Next.js · ZIP bomb protection

📚 Documentation • 💾 Install • ⚡ Quick Start • 🧩 Adapters • 🧬 YARA • 🤖 CI/CD • ❓ FAQ

Coverage badge reflects core library (src/**); adapters are measured separately.

• Overview
• Highlights
• Why pompelmi
• How it compares
• What Developers Say
• What Makes pompelmi Special
• Use Cases
• Installation
• Quick Start
  • Minimal Node usage
  • Express
  • Koa
  • Next.js (App Router)
• Configuration
• Security Notes
• Testing & Development
• FAQ
• Contributing
• License

pompelmi scans untrusted file uploads before they hit disk. A tiny, TypeScript-first toolkit for Node.js with composable scanners, deep ZIP inspection, and optional signature engines.

🔒 Private by design — no outbound calls; bytes never leave your process

🧩 Composable scanners — mix heuristics + signatures; set stopOn and timeouts

📦 ZIP hardening — traversal/bomb guards, polyglot & macro hints

🔌 Drop-in adapters — Express, Koa, Fastify, Next.js

📘 Typed & tiny — modern TS, minimal surface, tree-shakeable

⚡ Zero dependencies — core library has minimal deps, fast installation

🛡️ Block risky uploads early — classify uploads as clean, suspicious, or malicious and stop them at the edge.

✅ Real guards — extension allow‑list, server‑side MIME sniff (magic bytes), per‑file size caps, and deep ZIP traversal with anti‑bomb limits.

🔍 Built‑in scanners — drop‑in CommonHeuristicsScanner (PDF risky actions, Office macros, PE header) and Zip‑bomb Guard; add your own or YARA via a tiny { scan(bytes) } contract.

⚙️ Compose scanning — run multiple scanners in parallel or sequentially with timeouts and short‑circuiting via composeScanners().

☁️ Zero cloud — scans run in‑process. Keep bytes private. Perfect for GDPR/HIPAA compliance.

👨‍💻 DX first — TypeScript types, ESM/CJS builds, tiny API, adapters for popular web frameworks.

SEO Keywords: file upload security, malware detection, virus scanner, Node.js security, Express middleware, YARA integration, ZIP bomb protection, file validation, upload sanitization, threat detection, security scanner, antivirus Node.js, file scanning library, TypeScript security, Next.js security, Koa middleware, server-side validation, file integrity check, malware prevention, secure file upload

• On‑device, private scanning – no outbound calls, no data sharing.
• Blocks early – runs before you write to disk or persist anything.
• Fits your stack – drop‑in adapters for Express, Koa, Next.js (Fastify plugin in alpha).
• Defense‑in‑depth – ZIP traversal limits, ratio caps, server‑side MIME sniffing, size caps.
• Pluggable detection – bring your own engine (e.g., YARA) via a tiny { scan(bytes) } contract.

• Teams who can’t send uploads to third‑party AV APIs.
• Apps that need predictable, low‑latency decisions inline.
• Developers who want simple, typed building blocks instead of a daemon.

* You can run YARA alongside ClamAV, but it’s not built‑in.

"pompelmi made it incredibly easy to add malware scanning to our Express API. The TypeScript support is fantastic!" — Developer using pompelmi in production

"Finally, a file scanning solution that doesn't require sending our users' data to third parties. Perfect for GDPR compliance." — Security Engineer at a healthcare startup

"The YARA integration is seamless. We went from prototype to production in less than a week." — DevSecOps Engineer

Want to share your experience? Open a discussion!

Built with developers in mind from day one. Simple API, comprehensive TypeScript types, and excellent documentation mean you can integrate secure file scanning in minutes, not days. Hot module replacement support and detailed error messages make debugging a breeze.

Optimized for high-throughput scenarios with configurable concurrency, streaming support, and minimal memory overhead. Process thousands of files without breaking a sweat. Scans run in-process with no IPC overhead.

Multi-layered defense including MIME type verification (magic bytes), extension validation, size limits, ZIP bomb protection, and optional YARA integration. Each layer is configurable to match your threat model.

Your data never leaves your infrastructure. No telemetry, no cloud dependencies, no third-party API calls. Perfect for regulated industries (healthcare, finance, government) and privacy-conscious applications.

pompelmi is trusted across diverse industries and use cases:

Scan patient document uploads without sending PHI to third-party services. Keep medical records and imaging files secure on your infrastructure.

Validate customer document uploads (ID verification, tax forms) without exposing sensitive financial data to external APIs.

Protect learning management systems from malicious file uploads while maintaining student privacy.

Add secure file upload capabilities to your multi-tenant platform with per-tenant policy customization.

Scan files at ingestion time for corporate file sharing platforms, wikis, and collaboration tools.

Validate user-generated content uploads (images, videos, documents) before processing and storage.

# Express
npm i @pompelmi/express-middleware

# Koa
npm i @pompelmi/koa-middleware

# Next.js
npm i @pompelmi/next-upload

# Fastify (alpha)
npm i @pompelmi/fastify-plugin

Note: Core library works standalone. Install adapters only if using specific frameworks.

Optional dev deps used in the examples:

npm i -D tsx express multer @koa/router @koa/multer koa next

At a glance (policy + scanners)

// Compose built‑in scanners (no EICAR). Optionally add your own/YARA.
import { CommonHeuristicsScanner, createZipBombGuard, composeScanners } from 'pompelmi';

export const policy = {
  includeExtensions: ['zip','png','jpg','jpeg','pdf'],
  allowedMimeTypes: ['application/zip','image/png','image/jpeg','application/pdf','text/plain'],
  maxFileSizeBytes: 20 * 1024 * 1024,
  timeoutMs: 5000,
  concurrency: 4,
  failClosed: true,
  onScanEvent: (ev: unknown) => console.log('[scan]', ev)
};

export const scanner = composeScanners(
  [
    ['zipGuard', createZipBombGuard({ maxEntries: 512, maxTotalUncompressedBytes: 100 * 1024 * 1024, maxCompressionRatio: 12 })],
    ['heuristics', CommonHeuristicsScanner],
    // ['yara', YourYaraScanner],
  ],
  { parallel: false, stopOn: 'suspicious', timeoutMsPerScanner: 1500, tagSourceName: true }
);

import { scanFile } from 'pompelmi';

const res = await scanFile('path/to/file.zip'); // or any file
console.log(res.verdict); // "clean" | "suspicious" | "malicious"

See examples/scan-one-file.ts for a runnable script:

pnpm tsx examples/scan-one-file.ts ./path/to/file

import express from 'express';
import multer from 'multer';
import { createUploadGuard } from '@pompelmi/express-middleware';
import { policy, scanner } from './security'; // the snippet above

const app = express();
const upload = multer({ storage: multer.memoryStorage(), limits: { fileSize: policy.maxFileSizeBytes } });

app.post('/upload', upload.any(), createUploadGuard({ ...policy, scanner }), (req, res) => {
  res.json({ ok: true, scan: (req as any).pompelmi ?? null });
});

app.listen(3000, () => console.log('http://localhost:3000'));

import Koa from 'koa';
import Router from '@koa/router';
import multer from '@koa/multer';
import { createKoaUploadGuard } from '@pompelmi/koa-middleware';
import { policy, scanner } from './security';

const app = new Koa();
const router = new Router();
const upload = multer({ storage: multer.memoryStorage(), limits: { fileSize: policy.maxFileSizeBytes } });

router.post('/upload', upload.any(), createKoaUploadGuard({ ...policy, scanner }), (ctx) => {
  ctx.body = { ok: true, scan: (ctx as any).pompelmi ?? null };
});

app.use(router.routes()).use(router.allowedMethods());
app.listen(3003, () => console.log('http://localhost:3003'));

// app/api/upload/route.ts
import { createNextUploadHandler } from '@pompelmi/next-upload';
import { policy, scanner } from '@/lib/security';

export const runtime = 'nodejs';
export const dynamic = 'force-dynamic';

export const POST = createNextUploadHandler({ ...policy, scanner });

Run pompelmi in CI to scan repository files or built artifacts.

Minimal usage

name: Security scan (pompelmi)
on: [push, pull_request]

jobs:
  scan:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      - name: Scan repository with pompelmi
        uses: pompelmi/pompelmi/.github/actions/pompelmi-scan@v1
        with:
          path: .
          deep_zip: true
          fail_on_detect: true

Scan a single artifact

- uses: pompelmi/pompelmi/.github/actions/pompelmi-scan@v1
  with:
    artifact: build.zip
    deep_zip: true
    fail_on_detect: true

Inputs

The Action lives in this repo at .github/actions/pompelmi-scan. When published to the Marketplace, consumers can copy the snippets above as-is.

Use the adapter that matches your web framework. All adapters share the same policy options and scanning contract.

flowchart TD
  A["Client uploads file(s)"] --> B["Web App Route"]
  B --> C{"Pre-filters<br/>(ext, size, MIME)"}
  C -- fail --> X["HTTP 4xx"]
  C -- pass --> D{"Is ZIP?"}
  D -- yes --> E["Iterate entries<br/>(limits & scan)"]
  E --> F{"Verdict?"}
  D -- no --> F{"Scan bytes"}
  F -- malicious/suspicious --> Y["HTTP 422 blocked"]
  F -- clean --> Z["HTTP 200 ok + results"]

flowchart TD
  A["Client uploads file(s)"] --> B["Web App Route"]
  B --> C{"Pre-filters<br/>(ext, size, MIME)"}
  C -- fail --> X["HTTP 4xx"]
  C -- pass --> D{"Is ZIP?"}
  D -- yes --> E["Iterate entries<br/>(limits & scan)"]
  E --> F{"Verdict?"}
  D -- no --> F{"Scan bytes"}
  F -- malicious/suspicious --> Y["HTTP 422 blocked"]
  F -- clean --> Z["HTTP 200 ok + results"]

sequenceDiagram
  participant U as User
  participant A as App Route (/upload)
  participant P as pompelmi (adapter)
  participant Y as YARA engine

  U->>A: POST multipart/form-data
  A->>P: guard(files, policies)
  P->>P: MIME sniff + size + ext checks
  alt ZIP archive
    P->>P: unpack entries with limits
  end
  P->>Y: scan(bytes)
  Y-->>P: matches[]
  P-->>A: verdict (clean/suspicious/malicious)
  A-->>U: 200 or 4xx/422 with reason

sequenceDiagram
  participant U as User
  participant A as App Route (/upload)
  participant P as pompelmi (adapter)
  participant Y as YARA engine

  U->>A: POST multipart/form-data
  A->>P: guard(files, policies)
  P->>P: MIME sniff + size + ext checks
  alt ZIP archive
    P->>P: unpack entries with limits
  end
  P->>Y: scan(bytes)
  Y-->>P: matches[]
  P-->>A: verdict (clean/suspicious/malicious)
  A-->>U: 200 or 4xx/422 with reason

flowchart LR
  subgraph Repo
    core["pompelmi (core)"]
    express["@pompelmi/express-middleware"]
    koa["@pompelmi/koa-middleware"]
    next["@pompelmi/next-upload"]
    fastify(("fastify-plugin · planned"))
    nest(("nestjs · planned"))
    remix(("remix · planned"))
    hapi(("hapi-plugin · planned"))
    svelte(("sveltekit · planned"))
  end
  core --> express
  core --> koa
  core --> next
  core -.-> fastify
  core -.-> nest
  core -.-> remix
  core -.-> hapi
  core -.-> svelte

flowchart LR
  subgraph Repo
    core["pompelmi (core)"]
    express["@pompelmi/express-middleware"]
    koa["@pompelmi/koa-middleware"]
    next["@pompelmi/next-upload"]
    fastify(("fastify-plugin · planned"))
    nest(("nestjs · planned"))
    remix(("remix · planned"))
    hapi(("hapi-plugin · planned"))
    svelte(("sveltekit · planned"))
  end
  core --> express
  core --> koa
  core --> next
  core -.-> fastify
  core -.-> nest
  core -.-> remix
  core -.-> hapi
  core -.-> svelte

All adapters accept a common set of options:

Common recipes

Allow only images up to 5 MB:

includeExtensions: ['png','jpg','jpeg','webp'],
allowedMimeTypes: ['image/png','image/jpeg','image/webp'],
maxFileSizeBytes: 5 * 1024 * 1024,
failClosed: true,

• Limit file size aggressively (maxFileSizeBytes).
• Restrict extensions & MIME to what your app truly needs.
• Set failClosed: true in production to block on timeouts/errors.
• Handle ZIPs carefully (enable deep ZIP, keep nesting low, cap entry sizes).
• Compose scanners with composeScanners() and enable stopOn to fail fast on early detections.
• Log scan events (onScanEvent) and monitor for spikes.
• Run scans in a separate process/container for defense‑in‑depth when possible.
• Sanitize file names and paths if you persist uploads.
• Prefer memory storage + post‑processing; avoid writing untrusted bytes before policy passes.
• Add CI scanning with the GitHub Action to catch bad files in repos/artifacts.

YARA lets you detect suspicious or malicious content using pattern‑matching rules.
pompelmi treats YARA matches as signals that you can map to your own verdicts
(e.g., mark high‑confidence rules as malicious, heuristics as suspicious).

Status: Optional. You can run without YARA. If you adopt it, keep your rules small, time‑bound, and tuned to your threat model.

Below are three example rules you can adapt:

rules/starter/eicar.yar

rule EICAR_Test_File
{
    meta:
        description = "EICAR antivirus test string (safe)"
        reference   = "https://www.eicar.org"
        confidence  = "high"
        verdict     = "malicious"
    strings:
        $eicar = "X5O!P%@AP[4\\PZX54(P^)7CC)7}$EICAR-STANDARD-ANTIVIRUS-TEST-FILE!$H+H*"
    condition:
        $eicar
}

rules/starter/pdf_js.yar

rule PDF_JavaScript_Embedded
{
    meta:
        description = "PDF contains embedded JavaScript (heuristic)"
        confidence  = "medium"
        verdict     = "suspicious"
    strings:
        $magic = { 25 50 44 46 } // "%PDF"
        $js1 = "/JavaScript" ascii
        $js2 = "/JS" ascii
        $open = "/OpenAction" ascii
        $aa = "/AA" ascii
    condition:
        uint32(0) == 0x25504446 and ( $js1 or $js2 ) and ( $open or $aa )
}

rules/starter/office_macros.yar

rule Office_Macro_Suspicious_Words
{
    meta:
        description = "Heuristic: suspicious VBA macro keywords"
        confidence  = "medium"
        verdict     = "suspicious"
    strings:
        $s1 = /Auto(Open|Close)/ nocase
        $s2 = "Document_Open" nocase ascii
        $s3 = "CreateObject(" nocase ascii
        $s4 = "WScript.Shell" nocase ascii
        $s5 = "Shell(" nocase ascii
        $s6 = "Sub Workbook_Open()" nocase ascii
    condition:
        2 of ($s*)
}

These are examples. Expect some false positives; tune to your app.

If you use a YARA binding (e.g., @automattic/yara), wrap it behind the scanner contract:

// Example YARA scanner adapter (pseudo‑code)
import * as Y from '@automattic/yara';

// Compile your rules from disk at boot (recommended)
// const sources = await fs.readFile('rules/starter/*.yar', 'utf8');
// const compiled = await Y.compile(sources);

export const YourYaraScanner = {
  async scan(bytes: Uint8Array) {
    // const matches = await compiled.scan(bytes, { timeout: 1500 });
    const matches = []; // plug your engine here
    // Map to the structure your app expects; return [] when clean.
    return matches.map((m: any) => ({
      rule: m.rule,
      meta: m.meta ?? {},
      tags: m.tags ?? [],
    }));
  }
};

Then include it in your composed scanner:

import { composeScanners, CommonHeuristicsScanner } from 'pompelmi';
// import { YourYaraScanner } from './yara-scanner';

export const scanner = composeScanners(
  [
    ['heuristics', CommonHeuristicsScanner],
    // ['yara', YourYaraScanner],
  ],
  { parallel: false, stopOn: 'suspicious', timeoutMsPerScanner: 1500, tagSourceName: true }
);

• malicious: high‑confidence rules (e.g., EICAR_Test_File)
• suspicious: heuristic rules (e.g., PDF JavaScript, macro keywords)
• clean: no matches

Combine YARA with MIME sniffing, ZIP safety limits, and strict size/time caps.

Use the examples above, then send a minimal PDF that contains risky tokens (this triggers the built‑in heuristics).

1) Create a tiny PDF with risky actions

Linux:

printf '%%PDF-1.7\n1 0 obj\n<< /OpenAction 1 0 R /AA << /JavaScript (alert(1)) >> >>\nendobj\n%%EOF\n' > risky.pdf

macOS:

printf '%%PDF-1.7\n1 0 obj\n<< /OpenAction 1 0 R /AA << /JavaScript (alert(1)) >> >>\nendobj\n%%EOF\n' > risky.pdf

2) Send it to your endpoint

Express (default from the Quick‑start):

curl -F "file=@risky.pdf;type=application/pdf" http://localhost:3000/upload -i

You should see an HTTP 422 Unprocessable Entity (blocked by policy). Clean files return 200 OK. Pre‑filter failures (size/ext/MIME) should return a 4xx. Adapt these conventions to your app as needed.

• The library reads bytes; it never executes files.
• YARA detections depend on the rules you provide; expect some false positives/negatives.
• ZIP scanning applies limits (entries, per‑entry size, total uncompressed, nesting) to reduce archive‑bomb risk.
• Prefer running scans in a dedicated process/container for defense‑in‑depth.

[...]

• Changelog / releases: see GitHub Releases.
• Security disclosures: please use GitHub Security Advisories. We’ll coordinate a fix before public disclosure.
• Production users: open a Discussion to share requirements or request adapters.

pompelmi has been featured in leading developer publications and is trusted by teams worldwide for secure file upload handling.

• 💬 GitHub Discussions — Ask questions, share ideas
• 🐛 Issue Tracker — Report bugs, request features
• 📖 Documentation — Comprehensive guides and API reference
• 🔒 Security — Report security vulnerabilities privately

Do I need YARA?
No. scanner is pluggable. The examples use a minimal scanner for clarity; you can call out to a YARA engine or any other detector you prefer.

Where do the results live?
In the examples, the guard attaches scan data to the request context (e.g. req.pompelmi in Express, ctx.pompelmi in Koa). In Next.js, include the results in your JSON response as you see fit.

Why 422 for blocked files?
Using 422 to signal a policy violation keeps it distinct from transport errors; it’s a common pattern. Use the codes that best match your API guidelines.

Are ZIP bombs handled?
Archives are traversed with limits to reduce archive‑bomb risk. Keep your size limits conservative and prefer failClosed: true in production.

Run tests locally with coverage:

pnpm vitest run --coverage --passWithNoTests

The badge tracks the core library (src/**). Adapters and engines are reported separately for now and will be folded into global coverage as their suites grow.

If you integrate Codecov in CI, upload coverage/lcov.info and you can use this Codecov badge:

[![codecov](https://codecov.io/gh/pompelmi/pompelmi/branch/main/graph/badge.svg?flag=core)](https://codecov.io/gh/pompelmi/pompelmi)

PRs and issues welcome! Start with:

pnpm -r build
pnpm -r lint

See CONTRIBUTING.md for detailed guidelines.

Thanks to all the amazing contributors who have helped make pompelmi better!

• Official Docs — Complete API reference and guides
• Examples — Real-world integration examples
• Security Guide — Security best practices and disclosure policy

• File Upload Security in Node.js — Best practices guide (coming soon)
• Integrating YARA with pompelmi — Advanced detection setup (coming soon)
• Zero-Trust File Uploads — Architecture patterns (coming soon)

• GitHub Action — CI/CD scanning
• Docker Images — Containerized scanning (coming soon)
• Cloud Functions — Serverless examples (coming soon)

pompelmi stands on the shoulders of giants. Special thanks to:

• The YARA project for powerful pattern matching
• The Node.js community for excellent tooling
• All our contributors and users

Need help? We're here for you!

• 📖 Documentation
• 💬 GitHub Discussions
• 🐛 Issue Tracker
• 🔒 Security (for vulnerabilities)

For commercial support and consulting, contact the maintainers.

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MIT © 2025‑present pompelmi contributors