Situatie
1. Understand the Risks Behind Media Files
While formats like PNG and JPEG are generally safe, some file types can contain executable code or external resource calls, making them a potential security risk:
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SVG – Can embed JavaScript and CSS, enabling cross-site scripting (XSS) attacks
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PDF – May include malicious scripts or embedded executables
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Office documents – Can contain harmful macros
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Video files – Sometimes exploited via codec vulnerabilities.
If your website allows users to upload files, every file type you accept needs to be treated as potentially dangerous.
2. Sanitize and Validate File Uploads
Before storing any uploaded file, you should:
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Check the file extension and MIME type to ensure it matches the intended format
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Sanitize SVGs by removing
<script>tags,onloadevents, and any inline JavaScript -
Use antivirus scanning on all uploaded files
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Block disallowed file types unless explicitly needed.
Example for SVG sanitization:
Use libraries like DOMPurify or SVGO to strip malicious code before storing or serving the file.
3. Limit How Media Files Are Served
Even clean files can be abused if served incorrectly. To minimize risk:
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Serve media from a separate domain or subdomain (e.g.,
media.example.com) to isolate cookies and session data -
Set correct Content-Type headers so browsers interpret files correctly
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Apply Content Security Policy (CSP) headers to restrict what media can execute or load
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Disable inline script execution for formats like SVG.
4. Convert High-Risk Formats to Safer Alternatives
If your platform doesn’t absolutely need an SVG to remain in vector form, convert it to a PNG or WebP before display. This eliminates the risk of script execution while preserving the visual appearance.
5. Keep Your Platform Updated
Many attacks exploit old vulnerabilities in CMS platforms, plugins, or file-handling libraries.
Regularly updating your software stack ensures that known exploits are patched before attackers can use them.
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