A Dependency Vulnerability Put Our Users at Risk

Modern web apps are built on towers of dependencies. We had 847 packages in our node_modules folder. One of them had been vulnerable for 8 months, and we had no idea.

The Wake-Up Call

A security researcher emailed us on a Tuesday morning. They'd been auditing applications using a popular utility library and found us through Wappalyzer detection.

My first reaction was defensive. We barely use lodash directly. But then I checked our package-lock.json and found it was a dependency of a dependency. And yes, we were on a vulnerable version.

Understanding the Risk

Prototype pollution sounds academic until you realize what it means in practice:

• Attackers can modify the behavior of built-in JavaScript objects
• In Node.js, this can sometimes lead to remote code execution
• In browsers, it can enable XSS attacks or authentication bypasses
• The attack surface exists anywhere user input touches affected functions

We ran npm audit for the first time in months. The results were sobering.

$ npm audit
found 23 vulnerabilities (7 low, 12 moderate, 4 high)
  run `npm audit fix` to fix them

Twenty-three vulnerabilities. Four of them high severity. And we'd been ignoring this for who knows how long.

The Fix

The immediate fix was simple:

npm audit fix

# For the stubborn ones that needed manual intervention
npm update lodash
npm update minimist
npm update node-fetch

But some packages had breaking changes. We spent two days testing after updates, finding and fixing compatibility issues. It would have been much easier if we'd kept things updated incrementally.

Building Better Practices

After this incident, we implemented proper dependency management:

# .github/workflows/security.yml
name: Security Audit
on:
  push:
  schedule:
    - cron: '0 0 * * 1'  # Weekly Monday scan

jobs:
  audit:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - run: npm ci
      - run: npm audit --audit-level=moderate
      - uses: snyk/actions/node@master
        env:
          SNYK_TOKEN: ${{ secrets.SNYK_TOKEN }}

We also enabled Dependabot for automated pull requests when updates are available:

# .github/dependabot.yml
version: 2
updates:
  - package-ecosystem: "npm"
    directory: "/"
    schedule:
      interval: "weekly"
    open-pull-requests-limit: 10

The Hidden Cost of Neglect

The technical fix took half a day. But the real cost was the risk we'd unknowingly exposed our users to for months. A prototype pollution attack could have allowed:

• Session hijacking through manipulated objects
• Privilege escalation if user roles were object-based
• Data theft through modified API behavior
• Complete server compromise in worst-case scenarios

We were lucky. The researcher who found our vulnerability was ethical. Next time, we might not be so fortunate.

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