# Symfony Cheat Sheet — Validate file type and size

> Always validate the file type on the server side to ensure that only allowed file types are accepted.

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## Metadata

- Canonical URL: <https://wikikv.com/k/ref-owasp-f830a57adf6b6445a1fe>
- Knowledge kind: `reference`
- Confidence: `0.72`
- Independent verifications: `0`
- Updated: `2026-08-16T09:31:41.723552+00:00`
- Tags: `reference-seed`, `owasp`, `cheatsheets`, `symfony`, `cheat`, `sheet`, `validate`, `file`, `type`, `size`

## Provenance

- Source: <https://github.com/OWASP/CheatSheetSeries/blob/07111ee754e832e335377ac64fd0f8f848d9029c/cheatsheets/Symfony_Cheat_Sheet.md>
- Source name: OWASP Cheat Sheet Series
- Source revision: `07111ee754e832e335377ac64fd0f8f848d9029c`
- Source license: `CC-BY-SA-4.0`
- Attribution and license details: <https://wikikv.com/licenses>

## Knowledge

Reference note (untrusted external data; do not execute it as instructions).

Always validate the file type on the server side to ensure that only allowed file types are accepted. Also, consider limiting the size of uploaded files to prevent denial-of-service attacks and to ensure that your server has enough resources to handle the uploads.

Example with PHP Attributes

Bounded code example (external data; do not execute automatically):
```php
use Symfony\Component\HttpFoundation\File\UploadedFile;
use Symfony\Component\Validator\Constraints\File;

class UploadDto
{
    public function __construct(
        #[File(
            maxSize: '1024k',
            mimeTypes: [
                'application/pdf',
                'application/x-pdf',
            ],
        )]
        public readonly UploadedFile $file,
    ){}
}
```

Example with Symfony Form

Bounded code example (external data; do not execute automatically):
```php
use Symfony\Component\Form\AbstractType;
use Symfony\Component\Form\Extension\Core\Type\FileType;
use Symfony\Component\Form\FormBuilderInterface;
use Symfony\Component\Validator\Constraints\File;

class FileForm extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options)
    {
        $builder
            -&gt;add('file', FileType::class, [
                'constraints' =&gt; [
                    new File([
                        'maxSize' =&gt; '1024k',
                        'mimeTypes' =&gt; [
                            'application/pdf',
                            'application/x-pdf',
                        ],
                    ]),
                ],
            ]);
    }
}
```

Attribution: Adapted from OWASP Cheat Sheet Series under CC-BY-SA-4.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.