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🛡️ Sentinel: [HIGH] Fix XSS in WebView communication #109

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🛡️ Sentinel: [HIGH] Fix XSS in WebView communication #109

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4 changes: 4 additions & 0 deletions .jules/sentinel.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,4 @@
## 2025-02-17 - React Native WebView XSS via injectJavaScript
**Vulnerability:** Constructing stringified JavaScript payloads and inserting them directly via `WebView.injectJavaScript` inside `HomeScreen.tsx` and `ShiftScreen.tsx` (e.g. `window.runTesseract(${JSON.stringify(base64Json)});`) is susceptible to Cross-Site Scripting (XSS).
**Learning:** `injectJavaScript` behaves like `eval()` in a web context. If the data being injected isn't strictly controlled or escaped properly, a malicious payload inside an image base64 sequence or filename could theoretically escape the JSON string context and execute arbitrary JavaScript.
**Prevention:** Always use the postMessage API bridge for communicating between the React Native layer and the WebView. Establish event listeners (`window.addEventListener('message', ...)`) in the WebView's HTML template and invoke `webViewRef.current.postMessage(data)` from React Native.
16 changes: 7 additions & 9 deletions src/screens/HomeScreen.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -42,6 +42,11 @@ const weatherMap: Record<number, { text: string; icon: string }> = {
const engineHtml = `<!DOCTYPE html><html lang="it"><head>
<script src="https://cdn.jsdelivr.net/npm/tesseract.js@5/dist/tesseract.min.js"></script></head>
<body style="background-color:transparent;"><script>
const messageHandler = function(event) {
if (window.runTesseract) window.runTesseract(event.data);
};
window.addEventListener('message', messageHandler);
document.addEventListener('message', messageHandler);
window.runTesseract = async function(base64JsonStr) {
try {
const images = JSON.parse(base64JsonStr);
Expand Down Expand Up @@ -287,15 +292,8 @@ export default function HomeScreen() {
setProcessing(true); setOcrText('');
const base64List = result.assets.map(a => `data:image/jpeg;base64,${a.base64}`);
const base64Json = JSON.stringify(base64List);
// Use postMessage pattern to avoid script-injection risks with injectJavaScript
webViewRef.current?.injectJavaScript(`
if(window.runTesseract){
window.runTesseract(${JSON.stringify(base64Json)});
} else {
window.ReactNativeWebView.postMessage(JSON.stringify({success:false,error:'OCR non pronto'}));
}
true;
`);
// Use postMessage pattern to avoid script-injection risks
webViewRef.current?.postMessage(base64Json);
}
} catch (e) { if (__DEV__) console.error('[imagePicker]', e); setProcessing(false); }
};
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17 changes: 7 additions & 10 deletions src/screens/ShiftScreen.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -31,17 +31,9 @@ export default function ShiftScreen() {
setOcrText('');

const base64List = result.assets.map(a => `data:image/jpeg;base64,${a.base64}`);
const base64Json = JSON.stringify(base64List).replace(/'/g, "\\'");

const jsCode = `
if (window.runTesseract) {
window.runTesseract('${base64Json}');
} else {
window.ReactNativeWebView.postMessage(JSON.stringify({ success: false, error: "Motore OCR non pronto." }));
}
true;
`;
webViewRef.current?.injectJavaScript(jsCode);

webViewRef.current?.postMessage(JSON.stringify(base64List));
}
} catch (e) {
Alert.alert("Errore OCR", "Impossibile elaborare l'immagine.");
Expand Down Expand Up @@ -216,6 +208,11 @@ export default function ShiftScreen() {
</head>
<body style="background-color: transparent;">
<script>
const messageHandler = function(event) {
if (window.runTesseract) window.runTesseract(event.data);
};
window.addEventListener('message', messageHandler);
document.addEventListener('message', messageHandler);
window.runTesseract = async function(base64JsonStr) {
try {
const images = JSON.parse(base64JsonStr);
Expand Down
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