Add global isSafeURL utility

- Added isSafeURL utility based on prior work in gitlab-ee
- Also added isAbsoluteOrRootRelative() and getBaseURL() utils,
  needed by isSafeURL
- Removed URL() fallback because URL() is now polyfilled
- Updated specs

app/assets/javascripts/lib/utils/url_utility.js

@@ -121,4 +121,40 @@ export function webIDEUrl(route = undefined) {
   return returnUrl;
 }
 
+/**
+ * Returns current base URL
+ */
+export function getBaseURL() {
+  const { protocol, host } = window.location;
+  return `${protocol}//${host}`;
+}
+
+/**
+ * Returns true if url is an absolute or root-relative URL
+ *
+ * @param {String} url
+ */
+export function isAbsoluteOrRootRelative(url) {
+  return /^(https?:)?\//.test(url);
+}
+
+/**
+ * Checks if the provided URL is a safe URL (absolute http(s) or root-relative URL)
+ *
+ * @param {String} url that will be checked
+ * @returns {Boolean}
+ */
+export function isSafeURL(url) {
+  if (!isAbsoluteOrRootRelative(url)) {
+    return false;
+  }
+
+  try {
+    const parsedUrl = new URL(url, getBaseURL());
+    return ['http:', 'https:'].includes(parsedUrl.protocol);
+  } catch {
+    return false;
+  }
+}
+
 export { join as joinPaths } from 'path';

spec/javascripts/lib/utils/url_utility_spec.js → spec/frontend/lib/utils/url_utility_spec.js

@@ -107,4 +107,88 @@ describe('URL utility', () => {
       expect(url).toBe('/home/feature#install');
     });
   });
+
+  describe('getBaseURL', () => {
+    beforeEach(() => {
+      global.window = Object.create(window);
+      Object.defineProperty(window, 'location', {
+        value: {
+          host: 'gitlab.com',
+          protocol: 'https:',
+        },
+      });
+    });
+
+    it('returns correct base URL', () => {
+      expect(urlUtils.getBaseURL()).toBe('https://gitlab.com');
+    });
+  });
+
+  describe('isAbsoluteOrRootRelative', () => {
+    const validUrls = ['https://gitlab.com/', 'http://gitlab.com/', '/users/sign_in'];
+
+    const invalidUrls = [' https://gitlab.com/', './file/path', 'notanurl', '<a></a>'];
+
+    it.each(validUrls)(`returns true for %s`, url => {
+      expect(urlUtils.isAbsoluteOrRootRelative(url)).toBe(true);
+    });
+
+    it.each(invalidUrls)(`returns false for %s`, url => {
+      expect(urlUtils.isAbsoluteOrRootRelative(url)).toBe(false);
+    });
+  });
+
+  describe('isSafeUrl', () => {
+    const absoluteUrls = [
+      'http://example.org',
+      'http://example.org:8080',
+      'https://example.org',
+      'https://example.org:8080',
+      'https://192.168.1.1',
+    ];
+
+    const rootRelativeUrls = ['/relative/link'];
+
+    const relativeUrls = ['./relative/link', '../relative/link'];
+
+    const urlsWithoutHost = ['http://', 'https://', 'https:https:https:'];
+
+    /* eslint-disable no-script-url */
+    const nonHttpUrls = [
+      'javascript:',
+      'javascript:alert("XSS")',
+      'jav\tascript:alert("XSS");',
+      ' &#14;  javascript:alert("XSS");',
+      'ftp://192.168.1.1',
+      'file:///',
+      'file:///etc/hosts',
+    ];
+    /* eslint-enable no-script-url */
+
+    // javascript:alert('XSS')
+    const encodedJavaScriptUrls = [
+      '&#0000106&#0000097&#0000118&#0000097&#0000115&#0000099&#0000114&#0000105&#0000112&#0000116&#0000058&#0000097&#0000108&#0000101&#0000114&#0000116&#0000040&#0000039&#0000088&#0000083&#0000083&#0000039&#0000041',
+      '&#106;&#97;&#118;&#97;&#115;&#99;&#114;&#105;&#112;&#116;&#58;&#97;&#108;&#101;&#114;&#116;&#40;&#39;&#88;&#83;&#83;&#39;&#41;',
+      '&#x6A&#x61&#x76&#x61&#x73&#x63&#x72&#x69&#x70&#x74&#x3A&#x61&#x6C&#x65&#x72&#x74&#x28&#x27&#x58&#x53&#x53&#x27&#x29',
+      '\\u006A\\u0061\\u0076\\u0061\\u0073\\u0063\\u0072\\u0069\\u0070\\u0074\\u003A\\u0061\\u006C\\u0065\\u0072\\u0074\\u0028\\u0027\\u0058\\u0053\\u0053\\u0027\\u0029',
+    ];
+
+    const safeUrls = [...absoluteUrls, ...rootRelativeUrls];
+    const unsafeUrls = [
+      ...relativeUrls,
+      ...urlsWithoutHost,
+      ...nonHttpUrls,
+      ...encodedJavaScriptUrls,
+    ];
+
+    describe('with URL constructor support', () => {
+      it.each(safeUrls)('returns true for %s', url => {
+        expect(urlUtils.isSafeURL(url)).toBe(true);
+      });
+
+      it.each(unsafeUrls)('returns false for %s', url => {
+        expect(urlUtils.isSafeURL(url)).toBe(false);
+      });
+    });
+  });
 });