feat(security): enhance input sanitization and domain blocking

- Update `sanitizeInput` in `src/utils/security.ts` to escape backticks (`) to ``` preventing potential JS template literal injection.
- Add common disposable email domains (e.g., sharklasers.com, dispostable.com) to `BLOCKED_DOMAINS` in `src/utils/security.ts`.
- Update tests in `src/utils/security.test.ts` to verify new security measures.
- Record security learning in `.jules/sentinel.md`.

Co-authored-by: ragusa-it <196988693+ragusa-it@users.noreply.github.com>

.jules/sentinel.md

@@ -27,3 +27,8 @@
 **Vulnerability:** Allowing users to register or submit forms with disposable email addresses (e.g., mailinator.com) can lead to spam, abuse, and polluted data.
 **Learning:** While true email verification requires a backend or API, a simple client-side blocklist of common disposable domains is a highly effective, low-cost first line of defense.
 **Prevention:** Maintain a list of known disposable domains (e.g., `BLOCKED_DOMAINS`) and check the domain part of the email address during validation.
+
+## 2026-02-14 - Backtick Injection in Template Strings
+**Vulnerability:** Standard HTML sanitization often ignores backticks (` `), which can be dangerous if the sanitized string is injected into a JavaScript template literal context.
+**Learning:** While HTML entities (`<`, `"`) protect HTML contexts, modern JS uses backticks for strings. Failing to escape them allows attackers to break out of the string boundary if the data is used in a JS context.
+**Prevention:** Explicitly replace backticks with ``` in sanitization routines intended for general-purpose use.

src/utils/security.test.ts

@@ -10,6 +10,7 @@ describe('Security Utils', () => {
       expect(sanitizeInput('foo & bar')).toBe('foo & bar');
       expect(sanitizeInput('"quotes"')).toBe('"quotes"');
       expect(sanitizeInput("'single quotes'")).toBe(''single quotes'');
+      expect(sanitizeInput('`backticks`')).toBe('`backticks`');
       expect(sanitizeInput('>')).toBe('>');
     });
 
@@ -74,6 +75,8 @@ describe('Security Utils', () => {
       expect(isValidEmail('spam@mailinator.com')).toBe(false);
       expect(isValidEmail('bot@yopmail.com')).toBe(false);
       expect(isValidEmail('temp@temp-mail.org')).toBe(false);
+      expect(isValidEmail('spam@sharklasers.com')).toBe(false);
+      expect(isValidEmail('bot@maildrop.cc')).toBe(false);
     });
 
     it('rejects blocked domains regardless of case', () => {

src/utils/security.ts

@@ -14,7 +14,8 @@ export function sanitizeInput(input: string): string {
     .replace(/</g, "&lt;")
     .replace(/>/g, "&gt;")
     .replace(/"/g, "&quot;")
-    .replace(/'/g, "&#039;");
+    .replace(/'/g, "&#039;")
+    .replace(/`/g, "&#96;");
 }
 
 // Common disposable email providers and invalid domains
@@ -25,8 +26,13 @@ const BLOCKED_DOMAINS = new Set([
   "yopmail.com",
   "temp-mail.org",
   "guerrillamail.com",
+  "guerrillamail.net",
   "10minutemail.com",
   "trashmail.com",
+  "sharklasers.com",
+  "dispostable.com",
+  "maildrop.cc",
+  "getairmail.com",
 ]);
 
 /**