added allowRemoteMarkerIcons configuration option and restricted fetching of remote marker icons only when option is set to true;

asynchronously load all available icons in a settings object on server startup;
replaced fs.existsSync() call in serve_rendered when drawing marker icons with a check against available icons settings object;

docs/config.rst

@@ -32,6 +32,7 @@ Example:
       "serveAllFonts": false,
       "serveAllStyles": false,
       "serveStaticMaps": true,
+      "allowRemoteMarkerIcons": true,
       "tileMargin": 0
     },
     "styles": {
@@ -142,6 +143,13 @@ Optional string to be rendered into the raster tiles (and static maps) as waterm
 Can be used for hard-coding attributions etc. (can also be specified per-style).
 Not used by default.
 
+``allowRemoteMarkerIcons``
+--------------
+
+Allows the rendering of marker icons fetched via http(s) hyperlinks.
+For security reasons only allow this if you can control the origins from where the markers are fetched!
+Default is to disallow fetching of icons from remote sources.
+
 ``styles``
 ==========
 

package.json

@@ -39,7 +39,8 @@
     "proj4": "2.8.0",
     "request": "2.88.2",
     "sharp": "0.31.0",
-    "tileserver-gl-styles": "2.0.0"
+    "tileserver-gl-styles": "2.0.0",
+    "sanitize-filename": "1.6.3"
   },
   "devDependencies": {
     "chai": "4.3.6",

src/serve_rendered.js

@@ -8,10 +8,10 @@ import util from 'util';
 import zlib from 'zlib';
 import sharp from 'sharp'; // sharp has to be required before node-canvas. see https://github.com/lovell/sharp/issues/371
 import pkg from 'canvas';
-import Image from 'canvas';
 import clone from 'clone';
 import Color from 'color';
 import express from 'express';
+import sanitize from "sanitize-filename";
 import SphericalMercator from '@mapbox/sphericalmercator';
 import mlgl from '@maplibre/maplibre-gl-native';
 import MBTiles from '@mapbox/mbtiles';
@@ -22,7 +22,7 @@ import {getFontsPbf, getTileUrls, fixTileJSONCenter} from './utils.js';
 const FLOAT_PATTERN = '[+-]?(?:\\d+|\\d+\.?\\d+)';
 const httpTester = /^(http(s)?:)?\/\//;
 
-const {createCanvas} = pkg;
+const {createCanvas, Image} = pkg;
 const mercator = new SphericalMercator();
 const getScale = (scale) => (scale || '@1x').slice(1, 2) | 0;
 
@@ -231,11 +231,20 @@ const extractMarkersFromQuery = (query, options, transformer) => {
     // Check if icon is served via http otherwise marker icons are expected to
     // be provided as filepaths relative to configured icon path
     if (!(iconURI.startsWith('http://') || iconURI.startsWith('https://'))) {
-      iconURI = path.resolve(options.paths.icons, iconURI);
-      // Ensure icon exists at provided path
-      if (!fs.existsSync(iconURI)) {
+      // Sanitize URI with sanitize-filename
+      // https://www.npmjs.com/package/sanitize-filename#details
+      iconURI = sanitize(iconURI)
+
+      // If the selected icon is not part of available icons skip it
+      if (!options.paths.availableIcons.includes(iconURI)) {
         continue;
       }
+
+      iconURI = path.resolve(options.paths.icons, iconURI);
+
+    // When we encounter a remote icon check if the configuration explicitly allows them.
+    } else if (options.allowRemoteMarkerIcons !== true) {
+      continue;
     }
 
     // Ensure marker location could be parsed

src/server.js

@@ -95,6 +95,35 @@ export function server(opts) {
   checkPath('mbtiles');
   checkPath('icons');
 
+  /**
+ * Recursively get all files within a directory.
+ * Inspired by https://stackoverflow.com/a/45130990/10133863
+ * @param {String} directory Absolute path to a directory to get files from.
+ */
+  const getFiles = async (directory) => {
+    // Fetch all entries of the directory and attach type information
+    const dirEntries = await fs.promises.readdir(directory, { withFileTypes: true });
+
+    // Iterate through entries and return the relative file-path to the icon directory if it is not a directory
+    // otherwise initiate a recursive call
+    const files = await Promise.all(dirEntries.map((dirEntry) => {
+      const entryPath = path.resolve(directory, dirEntry.name);
+      return dirEntry.isDirectory() ?
+        getFiles(entryPath) : entryPath.replace(paths.icons + path.sep, "");
+    }));
+
+    // Flatten the list of files to a single array
+    return files.flat();
+  }
+
+  // Load all available icons into a settings object
+  startupPromises.push(new Promise(resolve => {
+    getFiles(paths.icons).then((files) => {
+      paths.availableIcons = files;
+      resolve();
+    });
+  }));
+
   if (options.dataDecorator) {
     try {
       options.dataDecoratorFunc = require(path.resolve(paths.root, options.dataDecorator));