fix: server crashes when receiving file download request with invalid byte range; this fixes a security vulnerability that allows an attacker to impact the availability of the server instance; the fix improves parsing of the range parameter to properly handle invalid range requests ([GHSA-h423-w6qv-2wj3](https://github.com/parse-community/parse-server/security/advisories/GHSA-h423-w6qv-2wj3)) [skip release] (#8237)

src/Adapters/Files/GridFSBucketAdapter.js

@@ -228,22 +228,35 @@ export class GridFSBucketAdapter extends FilesAdapter {
     const partialstart = parts[0];
     const partialend = parts[1];
 
-    const start = parseInt(partialstart, 10);
-    const end = partialend ? parseInt(partialend, 10) : files[0].length - 1;
+    const fileLength = files[0].length;
+    const fileStart = parseInt(partialstart, 10);
+    const fileEnd = partialend ? parseInt(partialend, 10) : fileLength;
 
-    res.writeHead(206, {
-      'Accept-Ranges': 'bytes',
-      'Content-Length': end - start + 1,
-      'Content-Range': 'bytes ' + start + '-' + end + '/' + files[0].length,
-      'Content-Type': contentType,
-    });
+    let start = Math.min(fileStart || 0, fileEnd, fileLength);
+    let end = Math.max(fileStart || 0, fileEnd) + 1 || fileLength;
+    if (isNaN(fileStart)) {
+      start = fileLength - end + 1;
+      end = fileLength;
+    }
+    end = Math.min(end, fileLength);
+    start = Math.max(start, 0);
+
+    res.status(206);
+    res.header('Accept-Ranges', 'bytes');
+    res.header('Content-Length', end - start);
+    res.header('Content-Range', 'bytes ' + start + '-' + end + '/' + fileLength);
+    res.header('Content-Type', contentType);
     const stream = bucket.openDownloadStreamByName(filename);
     stream.start(start);
+    if (end) {
+      stream.end(end);
+    }
     stream.on('data', chunk => {
       res.write(chunk);
     });
-    stream.on('error', () => {
-      res.sendStatus(404);
+    stream.on('error', (e) => {
+      res.status(404);
+      res.send(e.message);
     });
     stream.on('end', () => {
       res.end();

src/Routers/FilesRouter.js

@@ -266,5 +266,10 @@ export class FilesRouter {
 }
 
 function isFileStreamable(req, filesController) {
-  return req.get('Range') && typeof filesController.adapter.handleFileStream === 'function';
+  const range = (req.get('Range') || '/-/').split('-');
+  const start = Number(range[0]);
+  const end = Number(range[1]);
+  return (
+    (!isNaN(start) || !isNaN(end)) && typeof filesController.adapter.handleFileStream === 'function'
+  );
 }