[grade=A] P0-4: assets upload — wire decodeImageData helper (MIME whitelist + 5MB cap)

dashcaddy-api/routes/config/assets.js

@@ -15,6 +15,30 @@ const { ok, successMessage } = require('../../src/utils/responses');
  * @returns {express.Router}
  */
 
+// P0-4: image upload guard rails.
+// We allow a small whitelist of image MIME types and cap decoded bytes at 5 MB.
+const ALLOWED_IMAGE_TYPES = new Set(['png', 'jpeg', 'jpg', 'svg+xml', 'webp', 'ico', 'x-icon']);
+const MAX_ASSET_BYTES = 5 * 1024 * 1024;
+
+function decodeImageData(data) {
+  if (typeof data !== 'string') {
+    throw new ValidationError('Invalid image data format');
+  }
+  const matches = data.match(/^data:image\/([a-zA-Z0-9+.-]+);base64,(.+)$/);
+  if (!matches) {
+    throw new ValidationError('Invalid image data format');
+  }
+  const mime = matches[1].toLowerCase();
+  if (!ALLOWED_IMAGE_TYPES.has(mime)) {
+    throw new ValidationError(`Unsupported image type: ${mime}`);
+  }
+  const buffer = Buffer.from(matches[2], 'base64');
+  if (buffer.length > MAX_ASSET_BYTES) {
+    throw new ValidationError(`File too large (max ${MAX_ASSET_BYTES / 1024 / 1024}MB)`);
+  }
+  return { mime, buffer };
+}
+
 // Image processing for favicon conversion (optional)
 let sharp, pngToIco;
 try {
@@ -43,14 +67,10 @@ module.exports = function({ servicesStateManager: _servicesStateManager, asyncHa
       throw new ValidationError('Invalid filename - must not contain path separators');
     }
 
-    // Extract base64 data
-    const matches = data.match(/^data:image\/([a-zA-Z+]+);base64,(.+)$/);
-    if (!matches) {
-      throw new ValidationError('Invalid image data format');
-    }
-
-    const base64Data = matches[2];
-    const buffer = Buffer.from(base64Data, 'base64');
+    // P0-4 fix: use the helper that validates MIME type (whitelist), caps decoded bytes
+    // at 5 MB, and rejects anything that isn't a string. The old inline regex allowed
+    // `image/<anything>;base64,...` without a size cap and without MIME restriction.
+    const { buffer } = decodeImageData(data);
 
     // Determine assets path (mounted volume)
     const assetsPath = platformPaths.resolveAssetsPath(process.env.ASSETS_PATH);