Spam patterns and duplicate content are detected

Without spam detection, a single automated account can flood a community feed with duplicate or rapid-fire posts, drowning legitimate content and degrading the user experience to the point where real users leave. This is a CWE-770 (Allocation of Resources Without Limits) failure: uncapped post creation burns database storage and CDN bandwidth at attacker-controlled rates. Beyond quality, spam floods can mask coordinated manipulation campaigns — link farms, referral abuse, or coordinated inauthentic behavior — that are invisible without rate tracking.

Implement per-user rate limiting and content-hash deduplication on all post/comment submission handlers. In src/middleware/rateLimiter.ts:

import rateLimit from 'express-rate-limit';

export const postLimiter = rateLimit({
  windowMs: 5 * 60 * 1000, // 5 minutes
  max: 5,
  keyGenerator: (req) => req.user.id,
  message: 'Too many posts. Please wait before posting again.'
});

Pair rate limiting with a content-hash check: compute sha256(content) per user and reject exact duplicates submitted within the last hour. Reject at the API level before writing to the database.

• ID: community-moderation-safety.content-filtering.spam-detection

• Severity: low

• What to look for: Check for logic that detects spam: rapid repeated posting, duplicate content, suspicious patterns (many links, excessive hashtags), or third-party spam detection services. Look for rate limiting on post/comment submissions, or duplicate content comparison before save.

• Pass criteria: The system detects and handles spam: either rejects rapid postings from the same user, deduplicates identical content, or uses a third-party spam detection service. Count all post/comment submission handlers and verify that at least 1 spam-detection mechanism (rate limit, dedup, or spam API) is applied. Actions are taken before or immediately after content creation. Report the ratio of spam-protected endpoints to total submission endpoints even on pass.

• Fail criteria: No spam detection is implemented. Users can flood the platform with duplicate or rapid-fire content. A TODO comment or disabled spam check does not count as pass.

• Skip (N/A) when: Platform has <500 active users AND uses manual-only moderation.

• Detail on fail: "No spam detection implemented. A user can post identical content repeatedly or flood the platform with rapid postings."

• Remediation: Implement rate limiting and duplicate detection on post submissions:

  import { rateLimit } from 'express-rate-limit';
  
  // Rate limiting: 5 posts per 5 minutes per user
  const postLimiter = rateLimit({
    windowMs: 5 * 60 * 1000,
    max: 5,
    keyGenerator: (req) => req.user.id,
    message: 'Too many posts. Please wait before posting again.'
  });
  
  app.post('/api/posts', postLimiter, async (req, res) => {
    const { content } = req.body;
    const userId = req.user.id;
  
    // Check for duplicate content in the last hour
    const recentPost = await db.posts.findOne({
      content,
      userId,
      createdAt: { $gte: new Date(Date.now() - 3600000) }
    });
  
    if (recentPost) {
      return res.status(400).json({ error: 'You already posted this content recently' });
    }
  
    // Check for similar content using simple hash-based deduplication
    const contentHash = require('crypto').createHash('md5').update(content).digest('hex');
    const similar = await db.postHashes.findOne({ hash: contentHash, userId });
    if (similar) {
      return res.status(400).json({ error: 'Similar content already posted' });
    }
  
    // Save post
    const post = await db.posts.create({ content, userId, createdAt: new Date() });
    await db.postHashes.create({ hash: contentHash, userId, postId: post.id });
  
    res.status(201).json(post);
  });
  

  Reject posts that exceed the rate limit and flag exact duplicates.