Check for Subdomain Takeover in Symfony Easily

Introduction

Subdomain takeover is one of the most overlooked yet dangerous vulnerabilities in web applications. If your Symfony-powered site has unused or misconfigured subdomains, an attacker can hijack them, host malicious content, and tarnish your brand.

In this guide, we’ll show you how to check for subdomain takeover in Symfony, step-by-step — with Symfony-friendly code examples and using our Website Vulnerability Scanner online free.

You’ll also find links to our premium Web App Penetration Testing Services if you need deeper assessments, and you can subscribe to our security newsletter here: Subscribe on LinkedIn.

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What is Subdomain Takeover?

A subdomain takeover happens when a DNS record points to a service (like AWS, Heroku, or GitHub Pages) that’s no longer in use. The attacker claims the service under the same subdomain and gains full control of it.

Consequences include:

• Defacement or phishing on your domain

• Loss of trust

• Data breaches

That’s why every Symfony developer and DevOps team should proactively test and fix vulnerable DNS configurations.

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How to Detect Subdomain Takeover in Symfony

Here’s how you can approach it systematically:

1️⃣ Check Your DNS Records

Run a script to fetch all DNS records and spot CNAME or A records pointing to unclaimed services.

// src/Command/CheckSubdomainTakeoverCommand.php

namespace App\Command;

use Symfony\Component\Console\Command\Command;
use Symfony\Component\Console\Input\InputInterface;
use Symfony\Component\Console\Output\OutputInterface;
use Symfony\Contracts\HttpClient\HttpClientInterface;

class CheckSubdomainTakeoverCommand extends Command
{
    protected static $defaultName = 'app:check-subdomain-takeover';

    private $client;

    public function __construct(HttpClientInterface $client)
    {
        parent::__construct();
        $this->client = $client;
    }

    protected function execute(InputInterface $input, OutputInterface $output): int
    {
        $subdomains = [
            'test.yourdomain.com',
            'staging.yourdomain.com',
        ];

        foreach ($subdomains as $subdomain) {
            $response = $this->client->request('GET', 'http://' . $subdomain);
            $status = $response->getStatusCode();

            if ($status === 404 || str_contains($response->getContent(), 'No Such Bucket')) {
                $output->writeln("<error>Potentially vulnerable: $subdomain</error>");
            } else {
                $output->writeln("<info>Safe: $subdomain</info>");
            }
        }

        return Command::SUCCESS;
    }
}

Register and run this Symfony console command periodically. Adjust the $subdomains array with all known subdomains.

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2️⃣ Use Our Free Website Vulnerability Scanner

For a quick check, use our automated scanner at https://free.pentesttesting.com/.
It detects subdomain takeover risks, open ports, and much more.

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📷 Screenshot: Website Vulnerability Scanner

Screenshot of the free tools webpage where you can access security assessment tools.

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📷 Screenshot: Vulnerability Assessment Report

Sample Report generated by our free tool to check Website Vulnerability:

An Example of a vulnerability assessment report generated with our free tool, providing insights into possible vulnerabilities.

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Best Practices to Prevent Takeover

✅ Remove unused DNS records
✅ Use wildcard DNS sparingly
✅ Monitor subdomains for changes
✅ Regularly audit third-party services

For a full, manual audit and exploitation simulation, check our Web Application Penetration Testing Services.

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Why Symfony Developers Must Care

Symfony sites often rely on staging or preview environments (staging.yourdomain.com) and microservices. If those are decommissioned but DNS records remain, your attack surface grows.
By automating checks (like the code above), you can maintain control over all assets.

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Related Reading

You can also explore more security topics on our blog:
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Final Thoughts

Subdomain takeover is not hypothetical — it happens daily. Symfony sites are no exception. Run the console command, scan with our free tool, and keep your DNS tidy.

If you’d like a free scan right now, DM me or check: https://free.pentesttesting.com/