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🛡️ Sentinel: [security improvement] Harden CSP and secure event handlers #135

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🛡️ Sentinel: [security improvement] Harden CSP and secure event handlers #135

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5 changes: 5 additions & 0 deletions .jules/sentinel.md
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**Vulnerability:** Use of `innerHTML` for dynamic content and missing Content Security Policy (CSP).
**Learning:** Even if the content is currently static, using `innerHTML` is a dangerous pattern that can lead to XSS if the application grows. Prefer `textContent` and explicit DOM node creation.
**Prevention:** Establish a strong CSP and enforce secure DOM manipulation practices through documentation and code reviews.

## 2025-05-15 - CSP Hardening & Secure Event Handlers
**Vulnerability:** Weak CSP allowing form actions and reliance on inline property event handlers (`onclick`).
**Learning:** For static sites without forms, `form-action 'none'` provides defense-in-depth against unauthorized data exfiltration. Using `addEventListener` instead of `onclick` improves code clarity and follows modern security practices.
**Prevention:** Always set explicit button types and harden CSP directives like `form-action` and `base-uri` even if not immediately used. Use `addEventListener` for all dynamic elements.
9 changes: 6 additions & 3 deletions index.html
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<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<meta http-equiv="Content-Security-Policy" content="default-src 'self'; style-src 'self' 'sha256-fgxmLOznNmVf4GAd24jy5Eiv/Rer+7sVLOBqnsVx0nY='; script-src 'self' 'sha256-cPRnZP+O4z5KsN+vdFstQwgKExGtoN98I3Gq+Tm1aSA='; object-src 'none'; base-uri 'self'; upgrade-insecure-requests;">
<meta http-equiv="Content-Security-Policy" content="default-src 'self'; style-src 'self' 'sha256-fgxmLOznNmVf4GAd24jy5Eiv/Rer+7sVLOBqnsVx0nY='; script-src 'self' 'sha256-M6MErer+QDopN+Ivlj12GyByPCaRRGPWjKPHZVPjO+0='; object-src 'none'; base-uri 'self'; form-action 'none'; upgrade-insecure-requests;">
<meta name="referrer" content="no-referrer">
<title>5ive - UX Sample</title>
<style>
Expand Down Expand Up @@ -167,18 +167,21 @@ <h1>Welcome to 5ive</h1>
feedback.appendChild(content);

const closeBtn = document.createElement('button');
// ✅ Sentinel: Explicitly set type to prevent accidental form submission
closeBtn.type = 'button';
closeBtn.className = 'close-btn';
closeBtn.setAttribute('aria-label', 'Close notification');
closeBtn.textContent = '×';
closeBtn.onclick = () => {
// ✅ Sentinel: Use addEventListener instead of onclick for better security and flexibility
closeBtn.addEventListener('click', () => {
if (feedbackTimeout) clearTimeout(feedbackTimeout);
feedback.classList.remove('visible');
setTimeout(() => {
if (!feedback.classList.contains('visible')) {
feedback.textContent = '';
}
}, 300);
};
});
feedback.appendChild(closeBtn);

// Trigger reflow/transition
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