Add proper file upload validation in document-upload.service with security checks

[nanaf6203-bit]

Problem

File upload validation may rely on Content-Type header alone without magic byte verification, no virus scanning, and no path traversal prevention.

Expected Outcome

Defense-in-depth upload validation.

Acceptance Criteria

• MIME type via magic bytes, not just HTTP header
• Extension whitelist with MIME cross-validation
• ClamAV integration
• Path traversal prevention
• Type-specific size limits

Files Affected

src/documents/document-upload.service.ts, src/properties/property-images.service.ts, src/users/avatar-upload.service.ts

Difficulty

Medium

Estimated Effort

Medium (3-5 days)

Labels

security, file-upload, enhancement

[Thommyy7]

@Thommyy7 has applied to work on this issue as part of the Stellar Wave Program's 7th wave.

Hi, I'd like to work on this issue.

I have hands-on experience with backend development, databases, and API design, as well as frontend work with React and modern CSS. I write tested, maintainable code and enjoy contributing to open source projects.

I've reviewed the issue and I'm confident I can implement a solid solution while following the project's conventions.

Happy to get started right away if assigned — looking forward to contributing.

ℹ️ Repo Maintainers: To accept this application, review their application or assign @Thommyy7 to this issue.

[drips-wave]

Congratulations, @Thommyy7! 🎉 Your application was accepted by the repo's maintainers, and the issue is due on July 30, 2026.

🧑‍💻 @Thommyy7: Please resolve the issue such that the repo's maintainers have enough time to review your contribution before the due date. You'll earn Points for completing the issue on-time, which will make you eligible for a share of the Stellar Wave Program's reward pool.

Warning

When opening a PR, please link it to this issue to ensure it gets tracked accurately. Points are awarded when this issue is marked as completed by the maintainer.

🤠 Repo maintainers: Please keep an eye on the contributor's progress and review their work before the due date. You can manage this issue, including adjusting its complexity and points, here.

🌊 Happy Wave 🌊

[drips-wave]

This issue has been completed by @Thommyy7 as part of the Stellar Wave Program's 7th Wave 🥳

😎 @Thommyy7: You earned 200 Points for completing this issue! After the current Wave ends, you'll be eligible for a percentage of the Wave's reward pool based on the percentage of total points you've earned. Learn more here. You can also Leave a review to share your experience working on this issue.

🧑‍💻 Repo maintainers: How'd the contributor do? Leave a review to share your experience working with them.