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fix(security): remove allow-same-origin from MCP Apps sandbox iframes #1064

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fix(security): remove allow-same-origin from MCP Apps sandbox iframes #1064

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fix(security): remove allow-same-origin from MCP Apps sandbox iframes
zeroasterisk Apr 5, 2026
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zeroasterisk Apr 7, 2026
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3 changes: 1 addition & 2 deletions samples/client/lit/custom-components-example/ui/custom-components/mcp-apps-component.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -76,7 +76,6 @@ export class McpApp extends Root {
<iframe
id="mcp-sandbox"
referrerpolicy="origin"
sandbox="allow-scripts allow-forms allow-popups allow-modals allow-same-origin"
></iframe>
</div>
`;
Expand Down Expand Up @@ -176,7 +175,7 @@ export class McpApp extends Root {
// 4. Send the Inner HTML UI resource to the sandbox to spin up the actual app.
await this.bridge.sendSandboxResourceReady({
html: this.htmlContent,
sandbox: "allow-scripts allow-forms allow-popups allow-modals allow-same-origin"
sandbox: "allow-scripts allow-forms allow-popups allow-modals"
});
}

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2 changes: 1 addition & 1 deletion samples/client/shared/mcp_apps_inner_iframe/sandbox.ts
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Expand Up @@ -63,7 +63,7 @@ if (!disableSelfTest) {
// iframe on a separate origin. It creates an inner iframe for untrusted HTML content.
const inner = document.createElement("iframe");
inner.style.cssText = "width:100%; height:100%; border:none;";
inner.setAttribute("sandbox", "allow-scripts allow-same-origin allow-forms");
inner.setAttribute("sandbox", "allow-scripts allow-forms allow-popups allow-modals");
document.body.appendChild(inner);

const RESOURCE_READY_NOTIFICATION: McpUiSandboxResourceReadyNotification["method"] =
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