Security for UGC Platforms
UGC platforms accept and display content from users — text, images, files, and potentially code. Every piece of user content is a potential attack vector if not properly validated and sanitized.
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Why Security Matters for User-Generated Content Platforms
User-generated content is the #1 source of XSS vulnerabilities. When users can input text that's displayed to other users, stored XSS attacks can compromise every visitor. AI-generated code frequently renders user content without sanitization. File uploads add another dimension — malicious files can contain scripts, exploit image processing libraries, or consume excessive storage.
Security Risks
Stored XSS through user content
criticalMalicious JavaScript embedded in user posts, comments, or profiles, executing in other users' browsers.
Mitigation
Sanitize all user HTML with DOMPurify or similar. Use Content Security Policy. Never use dangerouslySetInnerHTML with user content.
Malicious file uploads
highUsers uploading executable files, oversized files, or files exploiting image processing vulnerabilities.
Mitigation
Validate file types server-side (check magic bytes, not just extension). Limit file sizes. Process images through a pipeline that strips metadata and re-encodes.
Content injection for phishing
mediumUsers creating content that mimics the platform UI to phish other users.
Mitigation
Clearly distinguish user content from platform UI. Strip HTML that mimics form elements, login prompts, or platform branding.
Security Checklist
Strip dangerous HTML tags and attributes from all user input before storage and display.
Restrict script execution sources as a defense-in-depth against XSS.
Verify file types, limit sizes, and process uploads through a sanitization pipeline.
Serve user-uploaded files from a different domain to prevent cookie theft via uploaded HTML.
Automated flagging of potentially harmful content with manual review queue.
Prevent spam bots from flooding the platform.
Real-World Scenario
A developer builds a recipe sharing site using Windsurf. Users can post recipes with rich text descriptions. The AI-generated code uses v-html in Vue to render formatted recipe text. An attacker posts a "recipe" containing a script that sends every visitor's session cookie to their server. Within a day, hundreds of accounts are compromised.
Frequently Asked Questions
What's the safest way to render user content?
Use Markdown instead of HTML. Libraries like react-markdown render Markdown safely without XSS risk. If you must allow HTML, use DOMPurify with a strict allowlist of safe tags and attributes.
How do I validate file uploads securely?
Don't trust file extensions. Read the file's magic bytes to verify the actual type. Limit file sizes. For images, re-encode them (this strips embedded scripts). Serve uploads from a separate domain or CDN.
Do I need content moderation?
If users can post content visible to other users, yes. At minimum, implement automated flagging for common patterns and a report button. Manual review for flagged content. Without moderation, your platform will be used for spam and abuse.
Security for Other Use Cases
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