fix: sonarqube denial of service issue

backend/src/utils.ts

@@ -10,9 +10,34 @@ export function formatPrice(cents: number): string {
   return `$${(cents / 100).toFixed(2)}`;
 }
 
-const EMAIL_RE = /^[^\s@]+@[^\s@]+\.[^\s@]+$/;
+// RFC 5321 caps an address at 254 characters; reject anything longer up front so
+// validation cost stays bounded regardless of what a client posts.
+const MAX_EMAIL_LENGTH = 254;
+
+// Both patterns are anchored single character classes with no overlapping
+// alternatives, so they match in linear time. Splitting on '@' and '.' in code
+// rather than in one combined pattern avoids the ambiguous (and backtracking)
+// `[^\s@]+\.[^\s@]+` domain match.
+const LOCAL_PART_RE = /^[^\s@]+$/;
+const DOMAIN_LABEL_RE = /^[^\s@.]+$/;
+
 export function isValidEmail(email: string): boolean {
-  return EMAIL_RE.test(email.trim());
+  const trimmed = email.trim();
+  if (trimmed.length === 0 || trimmed.length > MAX_EMAIL_LENGTH) {
+    return false;
+  }
+
+  const at = trimmed.indexOf('@');
+  if (at === -1 || at !== trimmed.lastIndexOf('@')) {
+    return false;
+  }
+
+  if (!LOCAL_PART_RE.test(trimmed.slice(0, at))) {
+    return false;
+  }
+
+  const labels = trimmed.slice(at + 1).split('.');
+  return labels.length >= 2 && labels.every((label) => DOMAIN_LABEL_RE.test(label));
 }
 
 export const MARKETING_CONSENT_TEXT =

backend/tests/unit/utils.test.ts

@@ -44,4 +44,31 @@ describe('isValidEmail', () => {
   it('rejects an email with no domain', () => {
     expect(isValidEmail('thom@')).toBe(false);
   });
+
+  it('accepts a multi-label domain', () => {
+    expect(isValidEmail('thom@mail.example.co.uk')).toBe(true);
+  });
+
+  it('rejects a domain with no dot', () => {
+    expect(isValidEmail('thom@localhost')).toBe(false);
+  });
+
+  it('rejects an empty domain label', () => {
+    expect(isValidEmail('thom@example..com')).toBe(false);
+    expect(isValidEmail('thom@.com')).toBe(false);
+  });
+
+  it('rejects more than one @', () => {
+    expect(isValidEmail('thom@foo@example.com')).toBe(false);
+  });
+
+  it('rejects an address longer than 254 characters', () => {
+    expect(isValidEmail(`${'a'.repeat(250)}@example.com`)).toBe(false);
+  });
+
+  it('rejects a long dotless domain without super-linear backtracking', () => {
+    const start = Date.now();
+    expect(isValidEmail(`thom@${'a'.repeat(60_000)}`)).toBe(false);
+    expect(Date.now() - start).toBeLessThan(1000);
+  });
 });