diff --git a/flutter/lib/models/model.dart b/flutter/lib/models/model.dart
index b2ac017d2..ed4f00ead 100644
--- a/flutter/lib/models/model.dart
+++ b/flutter/lib/models/model.dart
@@ -3494,6 +3494,11 @@ class CursorModel with ChangeNotifier {
     final hoty = double.parse(evt['hoty']);
     final width = int.parse(evt['width']);
     final height = int.parse(evt['height']);
+    // Bound physical allocation before density normalization or image decoding.
+    if (!_validCursorRasterSize(width.toDouble(), height.toDouble())) {
+      debugPrint('Rejected cursor $id: invalid source size ${width}x$height');
+      return;
+    }
     final pixelRatio = double.tryParse(evt['scale'] ?? '0');
     if (pixelRatio == null || !pixelRatio.isFinite || pixelRatio < 0 ||
         (pixelRatio > 0 &&
@@ -3502,6 +3507,11 @@ class CursorModel with ChangeNotifier {
       return;
     }
     List<dynamic> colors = json.decode(evt['colors']);
+    const bytesPerPixel = 4;
+    if (colors.length != width * height * bytesPerPixel) {
+      debugPrint('Rejected cursor $id: invalid RGBA length ${colors.length}');
+      return;
+    }
     final rgba = Uint8List.fromList(colors.map((s) => s as int).toList());
     final ui.Image? image;
     final platform = parent.target?.ffiModel.pi.platform;
diff --git a/flutter/test/cursor_source_validation_test.dart b/flutter/test/cursor_source_validation_test.dart
new file mode 100644
index 000000000..36f10c0d9
--- /dev/null
+++ b/flutter/test/cursor_source_validation_test.dart
@@ -0,0 +1,108 @@
+import 'dart:convert';
+
+import 'package:flutter/foundation.dart';
+import 'package:flutter_hbb/consts.dart';
+import 'package:flutter_hbb/models/model.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import 'cursor_test_utils.dart';
+
+const _side = 32;
+const _rgbaChannels = 4;
+const _sourceLimit = 4096;
+const _invalidSizes = [
+  (0, _side),
+  (-1, _side),
+  (_side, 0),
+  (_side, -1),
+  (_sourceLimit + 1, 1),
+  (1, _sourceLimit + 1),
+  (_sourceLimit * 4, _sourceLimit * 4),
+];
+
+void main() {
+  TestWidgetsFlutterBinding.ensureInitialized();
+  for (final platform in [
+    kPeerPlatformMacOS,
+    kPeerPlatformWindows,
+    kPeerPlatformLinux,
+  ]) {
+    for (final density in [null, '0', '4']) {
+      test('cursor source validation $platform density=$density',
+          () => _checkPackets(platform, density));
+    }
+  }
+}
+
+Future<void> _checkPackets(String platform, String? density) async {
+  final canvas = CursorTestCanvas(1, style: kRemoteViewStyleAdaptive, scale: 1);
+  final ffi = CursorTestFFI(canvas)..ffiModel.pi.platform = platform;
+  final cursor = CursorModel(WeakReference(ffi))..id = 'valid';
+  final messages = <String?>[];
+  final originalPrint = debugPrint;
+  debugPrint = (message, {wrapWidth}) => messages.add(message);
+  addTearDown(() {
+    debugPrint = originalPrint;
+    expect(cursor.parent.target, same(ffi));
+    cursor.disposeImages();
+    cursor.dispose();
+    canvas.dispose();
+  });
+  await cursor.updateCursorData(_event(density));
+  final previous = cursor.cache;
+  for (final length in [
+    0,
+    4,
+    _side * _side * _rgbaChannels - 1,
+    _side * _side * _rgbaChannels + 1
+  ]) {
+    await _expectRejected(cursor, _event(density, length: length));
+    expect(messages, contains(contains('RGBA length')));
+    messages.clear();
+  }
+  for (final (width, height) in _invalidSizes) {
+    // Invalid JSON detects decoding before geometry validation, without risking
+    // the oversized allocation if the production size check regresses.
+    final packet = _event(density, width: width, height: height, length: 4)
+      ..['colors'] = 'must not decode an invalid source size';
+    await _expectRejected(cursor, packet);
+    expect(messages, contains(contains('source size')));
+    messages.clear();
+  }
+  for (final (width, height) in [
+    (1, 1),
+    (_sourceLimit, 1),
+    (1, _sourceLimit)
+  ]) {
+    cursor.id = 'valid';
+    await cursor
+        .updateCursorData(_event(density, width: width, height: height));
+    expect((cursor.image!.width, cursor.image!.height), (width, height));
+    expect(cursor.cache, isNot(same(previous)));
+  }
+}
+
+Future<void> _expectRejected(
+    CursorModel cursor, Map<String, String> packet) async {
+  final previous = cursor.cache;
+  final image = cursor.image;
+  final hotspot = (cursor.hotx, cursor.hoty);
+  cursor.id = 'invalid';
+  await cursor.updateCursorData({...packet, 'id': 'invalid'});
+  expect(cursor.cache, same(previous));
+  expect(cursor.image, same(image));
+  expect((cursor.hotx, cursor.hoty), hotspot);
+}
+
+Map<String, String> _event(String? density,
+        {int width = _side, int height = _side, int? length}) =>
+    {
+      'id': 'valid',
+      'width': '$width',
+      'height': '$height',
+      'hotx': '0',
+      'hoty': '0',
+      if (density != null) 'scale': density,
+      'colors': jsonEncode(
+          List<int>.filled(length ?? width * height * _rgbaChannels, 255)),
+    };