Session tokens in secure HTTP-only cookies, SameSite=Strict

Session tokens stored in localStorage or accessible JavaScript variables are exfiltrable by any XSS payload on any page of the application. A single reflected or stored XSS vulnerability anywhere on the domain becomes a full session hijack with no additional effort. CWE-614 (Sensitive Cookie Without 'Secure' Attribute) and CWE-1004 (Sensitive Cookie Without 'HttpOnly' Flag) define these as distinct failures. OWASP A07 and PCI-DSS Req 6.4.1 mandate that session tokens be inaccessible to client-side scripts. In a financial application, exfiltrating a session token from localStorage via document.cookie or XSS requires zero CSRF bypass — the token is already JavaScript-readable and portable.

Configure session cookies with all three required attributes in src/lib/session.ts or the session middleware initialization:

session({
  cookie: {
    httpOnly: true,     // inaccessible to document.cookie and XSS
    secure: true,       // HTTPS transport only
    sameSite: 'Strict', // no cross-origin send (CSRF protection)
    maxAge: 15 * 60 * 1000
  }
})

Audit all calls to localStorage.setItem and sessionStorage.setItem in the codebase — no session token, auth token, or user identity value should appear as a storage key. Tokens are set exclusively by the server via Set-Cookie response headers; the client-side JavaScript never handles them.

• ID: finserv-session-security.session-integrity.token-security-httponly
• Severity: high
• What to look for: Count all cookie configuration settings and enumerate the security attributes: httpOnly, secure, sameSite. Quote the actual values found. Count all localStorage/sessionStorage token stores. Verify at least 3 cookie security attributes are set: httpOnly=true, secure=true, sameSite=Strict. A token stored in localStorage must not pass — do not pass if any session token is JavaScript-accessible.
• Pass criteria: Session tokens stored in cookies with at least 3 security attributes: httpOnly=true, secure=true, sameSite=Strict. Count all token storage locations — 0 must use localStorage/sessionStorage. Report the count even on pass (e.g., "Cookie config: httpOnly=true, secure=true, sameSite=Strict — 3 of 3 attributes set, 0 localStorage stores").
• Fail criteria: Session tokens in localStorage/sessionStorage (even 1 instance), or cookies lack any of: httpOnly, secure, or sameSite=Strict.
• Skip (N/A) when: The application uses stateless JWT with no cookies — cite the actual auth mechanism found.
• Detail on fail: "Session token in localStorage — JavaScript-accessible. 0 of 3 required cookie attributes (httpOnly, secure, sameSite) applicable" or "Cookie has httpOnly=true but secure=false — 2 of 3 required attributes set"
• Remediation: Use secure HTTP-only cookies (in src/lib/session.ts or session middleware config):

  // session middleware configuration
  session({
    cookie: {
      httpOnly: true,   // Prevent JavaScript access
      secure: true,     // HTTPS only
      sameSite: 'Strict', // Prevent CSRF
      maxAge: 15 * 60 * 1000, // 15 minutes
      domain: 'yourdomain.com'
    }
  })
  
  // Never store tokens in localStorage
  // localStorage.setItem('token', sessionToken); // DON'T DO THIS
  // Cookies are set automatically by the server