## Security Remediation Complete

All 4 Medium and 2 Low severity findings have been addressed:

### Medium Severity (Fixed)

**1. HTML Injection via Template Variables** (`template.service.ts:168`)
- Added `escapeHtml()` method with HTML entity encoding
- Variables substituted in HTML context are now properly escaped
- Handles &, <, >, ", and ' characters

**2. Rate Limit Cleanup Logic Bug** (`email.service.ts:16-23`)
- Created `RateLimitEntry` interface with `count` and `lastSentAt` fields
- Cleanup now correctly compares timestamps instead of counts
- Rate limiting will work effectively across cleanup cycles

**3. Open Redirect via URL Template Variables** (`template.service.ts`)
- Added `TRUSTED_DOMAINS` allowlist (shieldai.com, app.shieldai.com, api.shieldai.com)
- Added `validateUrl()` method that validates URLs against trusted domains
- Invalid URLs default to `/` to prevent phishing attacks

**4. In-Memory Deduplication Expiration** (`notification.service.ts:62-88`)
- Created `DeduplicationEntry` interface with `externalIds` and `expiresAt` fields
- In-memory dedup now respects the configured window_seconds TTL
- Prevents indefinite growth of pending deduplication sets

### Low Severity (Fixed)

**5. Zod Schema Validation** (`notification.config.ts`)
- `loadNotificationConfig()` now parses through `NotificationConfigSchema.parse()`
- Invalid configurations will throw at startup instead of runtime

**6. Email Format Validation** (`email.service.ts:33`)
- Added `EMAIL_PATTERN` regex for basic email validation
- Invalid email formats throw before attempting to send

### Test Results
- All 29 tests passing ✅
- No new TypeScript errors introduced

### Files Modified
- `packages/shared-notifications/src/services/template.service.ts`
- `packages/shared-notifications/src/services/email.service.ts`
- `packages/shared-notifications/src/services/notification.service.ts`
- `packages/shared-notifications/src/config/notification.config.ts`

### Next Action
Ready for Code Reviewer final review before marking security review complete.