De-AMP CSP Sandbox Bypass Test

What this tests

A page served with Content-Security-Policy: sandbox (no allow-* flags) is forbidden from navigating the top-level frame. A <meta http-equiv="refresh"> on such a page is refused.

Brave's De-AMP feature sniffs every text/html response for AMP markup plus a <link rel="canonical"> and redirects the top frame to that canonical URL. It does not inspect the response's CSP header, so a sandboxed page still gets navigated to its (attacker-controlled) canonical URL, bypassing the sandbox restriction.

Steps

1. Enable brave://settings/privacy → "Auto-redirect AMP pages" (on by default).
2. Open the sandboxed AMP page link below. If De-AMP ignores CSP you are redirected to /de-amp/csp-sandbox/landed.html. That is the bug.
3. Open the sandboxed meta-refresh control. You should stay put; the console shows the refresh was refused because the document is sandboxed. This confirms the header is otherwise honored.
4. Open the sandboxed AMP page in Chrome (no De-AMP). You should stay put, confirming De-AMP is the cause.

Test Links

1. Sandboxed AMP page (CSP: sandbox) -- De-AMP should NOT redirect, but does

2. Sandboxed meta-refresh (control) -- sandbox correctly blocks navigation

3. AMP page, no CSP (control) -- ordinary, expected De-AMP redirect

Expected results

Link	Protected browser	Vulnerable (current Brave)
1. Sandboxed AMP page	Stays on page	Redirected to landed.html
2. Sandboxed meta-refresh	Stays on page (refused)	Stays on page (refused)
3. AMP page, no CSP	Redirected (expected)	Redirected (expected)