fix: proper CSP handling in basic-host sandboxing (HTTP headers, worker-src, document.write) (#234)
* fix: Move CSP to HTTP headers + add worker-src, frameDomains, baseUriDomains, permissions Security improvements: - CSP is now set via HTTP headers in serve.ts instead of meta tags (meta tag CSP can be tampered with by same-origin content) - CSP passed as query param to sandbox.html for header-based enforcement New CSP/permissions features (borrowed from PR #158): - frameDomains: control frame-src directive for nested iframes - baseUriDomains: control base-uri directive - permissions: camera, microphone, geolocation via iframe allow attribute WebGL fix: - Use document.write() instead of srcdoc for inner iframe content (srcdoc creates opaque origin that breaks WebGL canvas updates) - Add worker-src directive with blob: support (critical for WebGL apps like CesiumJS/Three.js that use workers for tile decoding, terrain processing, image processing) 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com> * refactor: Remove permissions support (defer to PR #158) Keep this PR focused on CSP security fixes only. Permissions (camera, microphone, geolocation) will be handled in #158. 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com> * cleanup McpUiResourceCsp type usage / duplicate defs * fix: guard against CSP injection in domain parameters Validate CSP domain entries to reject characters that could: - Break out of CSP directives (semicolons, newlines) - Inject CSP keywords like 'unsafe-eval' (quotes) - Inject multiple sources in one entry (spaces) This prevents injection attacks where malicious domains could override the security policy. --------- Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>
This commit is contained in:
Olivier Chafik
GitHub
parent
df49e88b2d
commit
8b09f4278c
4 changed files with 572 additions and 155 deletions
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@ -1,10 +1,10 @@
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import { RESOURCE_MIME_TYPE, getToolUiResourceUri, type McpUiSandboxProxyReadyNotification, AppBridge, PostMessageTransport } from "@modelcontextprotocol/ext-apps/app-bridge";
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import { RESOURCE_MIME_TYPE, getToolUiResourceUri, type McpUiSandboxProxyReadyNotification, AppBridge, PostMessageTransport, type McpUiResourceCsp } from "@modelcontextprotocol/ext-apps/app-bridge";
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import { Client } from "@modelcontextprotocol/sdk/client/index.js";
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import { StreamableHTTPClientTransport } from "@modelcontextprotocol/sdk/client/streamableHttp.js";
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import type { CallToolResult, Tool } from "@modelcontextprotocol/sdk/types.js";
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const SANDBOX_PROXY_URL = new URL("http://localhost:8081/sandbox.html");
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const SANDBOX_PROXY_BASE_URL = "http://localhost:8081/sandbox.html";
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const IMPLEMENTATION = { name: "MCP Apps Host", version: "1.0.0" };
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@ -42,10 +42,7 @@ export async function connectToServer(serverUrl: URL): Promise<ServerInfo> {
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interface UiResourceData {
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html: string;
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csp?: {
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connectDomains?: string[];
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resourceDomains?: string[];
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};
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csp?: McpUiResourceCsp;
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}
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export interface ToolCallInfo {
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@ -120,7 +117,10 @@ async function getUiResource(serverInfo: ServerInfo, uri: string): Promise<UiRes
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}
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export function loadSandboxProxy(iframe: HTMLIFrameElement): Promise<boolean> {
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export function loadSandboxProxy(
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iframe: HTMLIFrameElement,
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csp?: McpUiResourceCsp,
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): Promise<boolean> {
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// Prevent reload
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if (iframe.src) return Promise.resolve(false);
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@ -140,8 +140,14 @@ export function loadSandboxProxy(iframe: HTMLIFrameElement): Promise<boolean> {
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window.addEventListener("message", listener);
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});
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log.info("Loading sandbox proxy...");
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iframe.src = SANDBOX_PROXY_URL.href;
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// Build sandbox URL with CSP query param for HTTP header-based CSP
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const sandboxUrl = new URL(SANDBOX_PROXY_BASE_URL);
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if (csp) {
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sandboxUrl.searchParams.set("csp", JSON.stringify(csp));
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}
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log.info("Loading sandbox proxy...", csp ? `(CSP: ${JSON.stringify(csp)})` : "");
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iframe.src = sandboxUrl.href;
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return readyPromise;
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}
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@ -263,16 +263,21 @@ function AppIFramePanel({ toolCallInfo, isDestroying, onTeardownComplete }: AppI
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useEffect(() => {
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const iframe = iframeRef.current!;
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loadSandboxProxy(iframe).then((firstTime) => {
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// The `firstTime` check guards against React Strict Mode's double
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// invocation (mount → unmount → remount simulation in development).
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// Outside of Strict Mode, this `useEffect` runs only once per
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// `toolCallInfo`.
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if (firstTime) {
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const appBridge = newAppBridge(toolCallInfo.serverInfo, iframe);
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appBridgeRef.current = appBridge;
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initializeApp(iframe, appBridge, toolCallInfo);
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}
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// First get CSP from resource, then load sandbox with CSP in query param
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// This ensures CSP is set via HTTP headers (tamper-proof)
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toolCallInfo.appResourcePromise.then(({ csp }) => {
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loadSandboxProxy(iframe, csp).then((firstTime) => {
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// The `firstTime` check guards against React Strict Mode's double
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// invocation (mount → unmount → remount simulation in development).
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// Outside of Strict Mode, this `useEffect` runs only once per
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// `toolCallInfo`.
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if (firstTime) {
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const appBridge = newAppBridge(toolCallInfo.serverInfo, iframe);
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appBridgeRef.current = appBridge;
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initializeApp(iframe, appBridge, toolCallInfo);
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}
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});
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});
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}, [toolCallInfo]);
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@ -62,26 +62,9 @@ const PROXY_READY_NOTIFICATION: McpUiSandboxProxyReadyNotification["method"] =
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// Special case: The "ui/notifications/sandbox-proxy-ready" message is
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// intercepted here (not relayed) because the Sandbox uses it to configure and
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// load the inner iframe with the Guest UI HTML content.
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// Build CSP meta tag from domains
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function buildCspMetaTag(csp?: { connectDomains?: string[]; resourceDomains?: string[] }): string {
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const resourceDomains = csp?.resourceDomains?.join(" ") ?? "";
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const connectDomains = csp?.connectDomains?.join(" ") ?? "";
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// Base CSP directives
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const directives = [
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"default-src 'self'",
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`script-src 'self' 'unsafe-inline' 'unsafe-eval' blob: data: ${resourceDomains}`.trim(),
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`style-src 'self' 'unsafe-inline' blob: data: ${resourceDomains}`.trim(),
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`img-src 'self' data: blob: ${resourceDomains}`.trim(),
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`font-src 'self' data: blob: ${resourceDomains}`.trim(),
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`connect-src 'self' ${connectDomains}`.trim(),
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"frame-src 'none'",
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"object-src 'none'",
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"base-uri 'self'",
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];
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return `<meta http-equiv="Content-Security-Policy" content="${directives.join("; ")}">`;
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}
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//
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// Security: CSP is enforced via HTTP headers on sandbox.html (set by serve.ts
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// based on ?csp= query param). This is tamper-proof unlike meta tags.
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window.addEventListener("message", async (event) => {
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if (event.source === window.parent) {
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@ -98,29 +81,26 @@ window.addEventListener("message", async (event) => {
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}
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if (event.data && event.data.method === RESOURCE_READY_NOTIFICATION) {
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const { html, sandbox, csp } = event.data.params;
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const { html, sandbox } = event.data.params;
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if (typeof sandbox === "string") {
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inner.setAttribute("sandbox", sandbox);
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}
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if (typeof html === "string") {
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// Inject CSP meta tag at the start of <head> if CSP is provided
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console.log("[Sandbox] Received CSP:", csp);
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let modifiedHtml = html;
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if (csp) {
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const cspMetaTag = buildCspMetaTag(csp);
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console.log("[Sandbox] Injecting CSP meta tag:", cspMetaTag);
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// Insert after <head> tag if present, otherwise prepend
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if (modifiedHtml.includes("<head>")) {
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modifiedHtml = modifiedHtml.replace("<head>", `<head>\n${cspMetaTag}`);
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} else if (modifiedHtml.includes("<head ")) {
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modifiedHtml = modifiedHtml.replace(/<head[^>]*>/, `$&\n${cspMetaTag}`);
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} else {
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modifiedHtml = cspMetaTag + modifiedHtml;
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}
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// Use document.write instead of srcdoc for WebGL compatibility.
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// srcdoc creates an opaque origin which prevents WebGL canvas updates
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// from being displayed properly. document.write preserves the sandbox
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// origin, allowing WebGL to work correctly.
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// CSP is enforced via HTTP headers on this page (sandbox.html).
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const doc = inner.contentDocument || inner.contentWindow?.document;
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if (doc) {
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doc.open();
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doc.write(html);
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doc.close();
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} else {
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console.log("[Sandbox] No CSP provided, using default");
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// Fallback to srcdoc if document is not accessible
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console.warn("[Sandbox] document.write not available, falling back to srcdoc");
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inner.srcdoc = html;
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}
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inner.srcdoc = modifiedHtml;
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}
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} else {
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if (inner && inner.contentWindow) {
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325
examples/basic-host/src/tamper-detection.ts
Normal file
325
examples/basic-host/src/tamper-detection.ts
Normal file
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@ -0,0 +1,325 @@
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/**
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* Tamper Detection Module for MCP-UI Sandbox
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*
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* Generates a script that monitors security-sensitive JavaScript APIs
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* and emits notifications when guest code accesses them.
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*/
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export type TamperRuleTarget =
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| "window"
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| "Element.prototype"
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| "Document.prototype"
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| "Node.prototype"
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| "HTMLElement.prototype"
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| "EventTarget.prototype"
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| "History.prototype"
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| "Location.prototype";
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export type TamperRuleType = "getter" | "method" | "both";
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export type TamperSeverity = "low" | "medium" | "high" | "critical";
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export interface TamperRule {
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target: TamperRuleTarget;
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property: string;
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type: TamperRuleType;
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severity: TamperSeverity;
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}
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export const TAMPER_DETECTED_NOTIFICATION =
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"ui/notifications/tamper-detected" as const;
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/**
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* Default rules for security-sensitive APIs.
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* - critical: Access is blocked (returns undefined / throws)
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* - high/medium/low: Access is allowed but an alert is emitted
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*/
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export const DEFAULT_TAMPER_RULES: TamperRule[] = [
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// === CRITICAL (blocked) ===
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// Escape attempts
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{ target: "window", property: "top", type: "getter", severity: "critical" },
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{
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target: "window",
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property: "parent",
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type: "getter",
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severity: "critical",
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},
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{
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target: "window",
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property: "opener",
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type: "getter",
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severity: "critical",
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},
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{
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target: "window",
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property: "frameElement",
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type: "getter",
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severity: "critical",
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},
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// Code execution
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{ target: "window", property: "eval", type: "method", severity: "critical" },
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// === HIGH (allowed with alert) ===
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{ target: "window", property: "Function", type: "getter", severity: "high" },
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// Network/data exfiltration
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{ target: "window", property: "fetch", type: "method", severity: "high" },
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{
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target: "window",
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property: "XMLHttpRequest",
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type: "getter",
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severity: "high",
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},
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{ target: "window", property: "WebSocket", type: "getter", severity: "high" },
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{
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target: "window",
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property: "EventSource",
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type: "getter",
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severity: "high",
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},
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// DOM injection (high-risk methods)
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{
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target: "Document.prototype",
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property: "write",
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type: "method",
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severity: "high",
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},
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{
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target: "Document.prototype",
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property: "writeln",
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type: "method",
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severity: "high",
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},
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{
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target: "Element.prototype",
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property: "insertAdjacentHTML",
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type: "method",
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severity: "high",
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},
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// === MEDIUM (allowed with alert) ===
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// Storage access
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{
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target: "window",
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property: "localStorage",
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type: "getter",
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severity: "medium",
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},
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{
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target: "window",
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property: "sessionStorage",
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type: "getter",
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severity: "medium",
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},
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{
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target: "window",
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property: "indexedDB",
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type: "getter",
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severity: "medium",
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},
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{ target: "window", property: "caches", type: "getter", severity: "medium" },
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// DOM injection (property-based)
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{
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target: "Element.prototype",
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property: "innerHTML",
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type: "both",
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severity: "medium",
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},
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{
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target: "Element.prototype",
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property: "outerHTML",
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type: "both",
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severity: "medium",
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},
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// DOM traversal
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{
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target: "Node.prototype",
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property: "parentNode",
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type: "getter",
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severity: "medium",
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},
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{
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target: "Node.prototype",
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property: "parentElement",
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type: "getter",
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severity: "medium",
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},
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{
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target: "Element.prototype",
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property: "closest",
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type: "method",
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severity: "medium",
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},
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// History manipulation
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{ target: "window", property: "history", type: "getter", severity: "medium" },
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{
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target: "window",
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property: "location",
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type: "getter",
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severity: "medium",
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},
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// === LOW (allowed with alert) ===
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// Message passing
|
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{
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target: "window",
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property: "postMessage",
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type: "method",
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severity: "low",
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},
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// DOM queries
|
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{
|
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target: "Document.prototype",
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property: "querySelector",
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type: "method",
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severity: "low",
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},
|
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{
|
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target: "Document.prototype",
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property: "querySelectorAll",
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type: "method",
|
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severity: "low",
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},
|
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{
|
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target: "Document.prototype",
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property: "getElementById",
|
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type: "method",
|
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severity: "low",
|
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},
|
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];
|
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|
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/**
|
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* Generates the tamper detection script as a string.
|
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* This script should be injected into guest HTML before any other scripts run.
|
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*/
|
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export function generateTamperDetectionScript(
|
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rules: TamperRule[] = DEFAULT_TAMPER_RULES,
|
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): string {
|
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const rulesJson = JSON.stringify(rules);
|
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|
||||
return `(function() {
|
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'use strict';
|
||||
|
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var NOTIFICATION_METHOD = '${TAMPER_DETECTED_NOTIFICATION}';
|
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var rules = ${rulesJson};
|
||||
|
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function emitTamperAlert(rule, accessType, stackTrace) {
|
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try {
|
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window.parent.postMessage({
|
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jsonrpc: '2.0',
|
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method: NOTIFICATION_METHOD,
|
||||
params: {
|
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property: rule.target + '.' + rule.property,
|
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accessType: accessType,
|
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severity: rule.severity,
|
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blocked: rule.severity === 'critical',
|
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timestamp: Date.now(),
|
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stack: stackTrace
|
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}
|
||||
}, '*');
|
||||
} catch (e) {
|
||||
// Silently fail if postMessage is unavailable
|
||||
}
|
||||
}
|
||||
|
||||
function shouldBlock(rule) {
|
||||
return rule.severity === 'critical';
|
||||
}
|
||||
|
||||
function wrapProperty(target, prop, rule) {
|
||||
var descriptor = Object.getOwnPropertyDescriptor(target, prop);
|
||||
if (!descriptor) return false;
|
||||
|
||||
var newDescriptor = {
|
||||
configurable: false,
|
||||
enumerable: descriptor.enumerable
|
||||
};
|
||||
|
||||
var wrapped = false;
|
||||
|
||||
if (rule.type === 'getter' || rule.type === 'both') {
|
||||
var originalGetter = descriptor.get || (function() { return descriptor.value; });
|
||||
newDescriptor.get = function() {
|
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emitTamperAlert(rule, 'read', new Error().stack);
|
||||
if (shouldBlock(rule)) {
|
||||
return undefined;
|
||||
}
|
||||
return originalGetter.call(this);
|
||||
};
|
||||
wrapped = true;
|
||||
}
|
||||
|
||||
if (rule.type === 'method' && typeof descriptor.value === 'function') {
|
||||
var originalMethod = descriptor.value;
|
||||
newDescriptor.value = function() {
|
||||
emitTamperAlert(rule, 'call', new Error().stack);
|
||||
if (shouldBlock(rule)) {
|
||||
throw new Error('Access to ' + rule.target + '.' + rule.property + ' is blocked');
|
||||
}
|
||||
return originalMethod.apply(this, arguments);
|
||||
};
|
||||
wrapped = true;
|
||||
}
|
||||
|
||||
if (rule.type === 'both' && descriptor.set) {
|
||||
var originalSetter = descriptor.set;
|
||||
newDescriptor.set = function(value) {
|
||||
emitTamperAlert(rule, 'write', new Error().stack);
|
||||
if (shouldBlock(rule)) {
|
||||
return;
|
||||
}
|
||||
return originalSetter.call(this, value);
|
||||
};
|
||||
}
|
||||
|
||||
if (wrapped) {
|
||||
try {
|
||||
Object.defineProperty(target, prop, newDescriptor);
|
||||
return true;
|
||||
} catch (e) {
|
||||
return false;
|
||||
}
|
||||
}
|
||||
return false;
|
||||
}
|
||||
|
||||
function getTargetObject(targetName) {
|
||||
switch (targetName) {
|
||||
case 'window': return window;
|
||||
case 'Element.prototype': return Element.prototype;
|
||||
case 'Document.prototype': return Document.prototype;
|
||||
case 'Node.prototype': return Node.prototype;
|
||||
case 'HTMLElement.prototype': return HTMLElement.prototype;
|
||||
case 'EventTarget.prototype': return EventTarget.prototype;
|
||||
case 'History.prototype': return History.prototype;
|
||||
case 'Location.prototype': return Location.prototype;
|
||||
default: return null;
|
||||
}
|
||||
}
|
||||
|
||||
// Install monitoring
|
||||
for (var i = 0; i < rules.length; i++) {
|
||||
var rule = rules[i];
|
||||
var target = getTargetObject(rule.target);
|
||||
if (target) {
|
||||
wrapProperty(target, rule.property, rule);
|
||||
}
|
||||
}
|
||||
})();`;
|
||||
}
|
||||
|
||||
/**
|
||||
* Injects a script into HTML content, ensuring it runs before any other scripts.
|
||||
*/
|
||||
export function injectScriptIntoHtml(html: string, script: string): string {
|
||||
const scriptTag = `<script>${script}</script>`;
|
||||
|
||||
// Try <head> first
|
||||
if (html.includes("<head>")) {
|
||||
return html.replace("<head>", `<head>${scriptTag}`);
|
||||
}
|
||||
// Try <body>
|
||||
if (html.includes("<body>")) {
|
||||
return html.replace("<body>", `<body>${scriptTag}`);
|
||||
}
|
||||
// Fallback: prepend
|
||||
return scriptTag + html;
|
||||
}
|
||||
Loading…
Reference in a new issue