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🛡️ Sentinel: [HIGH] Fix XSS vulnerability in WebView OCR injection #139

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🛡️ Sentinel: [HIGH] Fix XSS vulnerability in WebView OCR injection #139

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7 changes: 7 additions & 0 deletions .jules/sentinel.md
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Original file line number Diff line number Diff line change
@@ -0,0 +1,7 @@
## 2026-04-27 - XSS in React Native WebView

**Vulnerability:** React Native WebViews `injectJavaScript` was using unsafe string interpolation with base64 images that could lead to XSS attacks or syntax errors if the string contained single or double quotes unescaped correctly.

**Learning:** Passing user-supplied strings directly into `injectJavaScript` using template interpolation exposes a risk for Script Injection/XSS in WebViews.

**Prevention:** To avoid this, prefer establishing a two-way communication channel using `postMessage` (from WebView to React Native) and `webViewRef.current?.postMessage` (from React Native to WebView). Ensure the HTML snippet adds `message` listeners for both `window` and `document`, and uses a `READY` message handshake to confirm the engine is ready.
52 changes: 35 additions & 17 deletions src/screens/HomeScreen.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -42,19 +42,41 @@ 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>
window.runTesseract = async function(base64JsonStr) {
// Prevent XSS by using postMessage instead of string interpolation
window.addEventListener('message', async function(event) {
try {
const images = JSON.parse(base64JsonStr);
let combinedText = '';
for (let i = 0; i < images.length; i++) {
const ret = await Tesseract.recognize(images[i], 'ita+eng');
combinedText += ret.data.text + '\\n\\n';
const data = JSON.parse(event.data);
if (data.type === 'RUN_OCR') {
const images = data.images;
let combinedText = '';
for (let i = 0; i < images.length; i++) {
const ret = await Tesseract.recognize(images[i], 'ita+eng');
combinedText += ret.data.text + '\\n\\n';
}
window.ReactNativeWebView.postMessage(JSON.stringify({ success: true, text: combinedText }));
}
window.ReactNativeWebView.postMessage(JSON.stringify({ success: true, text: combinedText }));
} catch (e) {
window.ReactNativeWebView.postMessage(JSON.stringify({ success: false, error: e.message || e.toString() }));
}
};
});
document.addEventListener('message', async function(event) {
try {
const data = JSON.parse(event.data);
if (data.type === 'RUN_OCR') {
const images = data.images;
let combinedText = '';
for (let i = 0; i < images.length; i++) {
const ret = await Tesseract.recognize(images[i], 'ita+eng');
combinedText += ret.data.text + '\\n\\n';
}
window.ReactNativeWebView.postMessage(JSON.stringify({ success: true, text: combinedText }));
}
} catch (e) {
window.ReactNativeWebView.postMessage(JSON.stringify({ success: false, error: e.message || e.toString() }));
}
});
// Handshake to notify React Native that WebView is ready
window.ReactNativeWebView.postMessage(JSON.stringify({ type: 'READY' }));
</script></body></html>`;

function PinnedFlightCardComponent({ item, colors }: { item: any; colors: any }) {
Expand Down Expand Up @@ -289,23 +311,19 @@ export default function HomeScreen({ isFocused }: { isFocused?: boolean }) {
setImageList(result.assets.map(a => a.uri));
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;
`);
webViewRef.current?.postMessage(JSON.stringify({ type: 'RUN_OCR', images: base64List }));
}
} catch (e) { if (__DEV__) console.error('[imagePicker]', e); setProcessing(false); }
};

const handleWebViewMessage = (event: any) => {
try {
const r = JSON.parse(event.nativeEvent.data);
if (r.type === 'READY') {
// Engine is ready, can proceed with messages if needed
return;
}
if (r.success) setOcrText(r.text);
else Alert.alert('Errore riconoscimento testo', r.error || 'Prova con un\'immagine più nitida o meglio illuminata.');
} catch (e) { if (__DEV__) console.error('[ocrMessage]', e); } finally { setProcessing(false); }
Expand Down
54 changes: 35 additions & 19 deletions src/screens/ShiftScreen.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -31,17 +31,7 @@ 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({ type: 'RUN_OCR', images: base64List }));
}
} catch (e) {
Alert.alert("Errore OCR", "Impossibile elaborare l'immagine.");
Expand All @@ -53,6 +43,10 @@ export default function ShiftScreen() {
const rawData = event.nativeEvent.data;
try {
const result = JSON.parse(rawData);
if (result.type === 'READY') {
// Engine is ready
return;
}
if (result.success) {
setOcrText(result.text);
} else {
Expand Down Expand Up @@ -216,19 +210,41 @@ export default function ShiftScreen() {
</head>
<body style="background-color: transparent;">
<script>
window.runTesseract = async function(base64JsonStr) {
// Prevent XSS by using postMessage instead of string interpolation
window.addEventListener('message', async function(event) {
try {
const data = JSON.parse(event.data);
if (data.type === 'RUN_OCR') {
const images = data.images;
let combinedText = '';
for (let i = 0; i < images.length; i++) {
const ret = await Tesseract.recognize(images[i], 'ita+eng');
combinedText += ret.data.text + '\\n\\n';
}
window.ReactNativeWebView.postMessage(JSON.stringify({ success: true, text: combinedText }));
}
} catch (e) {
window.ReactNativeWebView.postMessage(JSON.stringify({ success: false, error: e.message || e.toString() }));
}
});
document.addEventListener('message', async function(event) {
try {
const images = JSON.parse(base64JsonStr);
let combinedText = '';
for (let i = 0; i < images.length; i++) {
const ret = await Tesseract.recognize(images[i], 'ita+eng');
combinedText += ret.data.text + '\\n\\n';
const data = JSON.parse(event.data);
if (data.type === 'RUN_OCR') {
const images = data.images;
let combinedText = '';
for (let i = 0; i < images.length; i++) {
const ret = await Tesseract.recognize(images[i], 'ita+eng');
combinedText += ret.data.text + '\\n\\n';
}
window.ReactNativeWebView.postMessage(JSON.stringify({ success: true, text: combinedText }));
}
window.ReactNativeWebView.postMessage(JSON.stringify({ success: true, text: combinedText }));
} catch (e) {
window.ReactNativeWebView.postMessage(JSON.stringify({ success: false, error: e.message || e.toString() }));
}
};
});
// Handshake to notify React Native that WebView is ready
window.ReactNativeWebView.postMessage(JSON.stringify({ type: 'READY' }));
</script>
</body>
</html>
Expand Down
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