A dot is not a hostname

packages/feed/src/discover.js

@@ -52,14 +52,69 @@ export function normalizeUrl(input) {
   try {
     const u = new URL(raw);
     if (u.protocol !== 'http:' && u.protocol !== 'https:') return null;
-    if (!u.hostname.includes('.')) return null;
+    if (!plausibleHost(u.hostname)) return null;
     u.hash = '';
     return u.toString();
   } catch {
     return null;
   }
 }
 
+/**
+ * Is this hostname something a publisher could actually be at?
+ *
+ * `new URL()` is far more permissive about hosts than DNS is. Quotes, parens,
+ * `=` and `&` are not forbidden host code points, so `new URL('https://x')`
+ * happily parses `version="1.0"`, `zombies.)` and `z.` into a hostname — and
+ * the check this replaced, `hostname.includes('.')`, waved all three through.
+ *
+ * That is not a theoretical gap. The bulk-upload scanner splits pasted text on
+ * whitespace and offers every token as a URL, so pasting raw OPML instead of a
+ * URL list turned the markup itself into feeds: `https://version="1.0"/`,
+ * `https://text="gg.deals/`, and a sentence ending in "zombies." into
+ * `https://zombies.)/`. Roughly 3,700 such rows reached the directory, and
+ * every one of them is crawled forever on a cadence, failing `blocked-host`.
+ *
+ * Validating here rather than in the scanner is deliberate: `normalizeUrl` is
+ * the single gate every entry path goes through -- web submit, OPML import,
+ * the queue drain and discovery -- so one check covers all of them, and the
+ * scanner cannot import this module anyway (it runs in the browser, and
+ * pulling `@rssamplifier/feed` into client code fails the build on `node:dns`).
+ *
+ * Kept deliberately loose about what a real domain looks like: this rejects
+ * things that cannot be hostnames, not things that are merely unusual. IDN is
+ * already punycode by the time it arrives, and a bare IPv4 literal is allowed
+ * through so that a feed genuinely served from one is not newly rejected --
+ * private ranges are refused later, by `isPublicHost`.
+ *
+ * @param {string} hostname as parsed by `new URL`, so lowercased and punycoded
+ * @returns {boolean}
+ */
+function plausibleHost(hostname) {
+  const host = String(hostname ?? '');
+  if (!host || host.length > 253) return false;
+
+  // A dotted-quad is a legitimate, if unusual, place for a feed to live.
+  if (/^\d{1,3}(\.\d{1,3}){3}$/.test(host)) {
+    return host.split('.').every((n) => Number(n) <= 255);
+  }
+
+  // Anything outside the DNS alphabet is markup or prose, not a host.
+  if (!/^[a-z0-9.-]+$/.test(host)) return false;
+
+  const labels = host.split('.');
+  // Two labels at least, none empty -- which is what rules out `z.` and `you.`,
+  // whose trailing dot leaves an empty final label.
+  if (labels.length < 2) return false;
+  if (labels.some((l) => l === '' || l.length > 63 || l.startsWith('-') || l.endsWith('-'))) {
+    return false;
+  }
+
+  // A public suffix is letters. This is the part that rejects `1.0` while
+  // leaving `example.co.uk` and `xn--bcher-kva.de` alone.
+  return /^[a-z]{2,}$/.test(labels[labels.length - 1]);
+}
+
 /**
  * Extract feed URLs advertised by a page's <link rel="alternate"> tags.
  *

packages/feed/test/security.test.js

@@ -47,6 +47,44 @@ test('normalizeUrl adds a scheme but rejects dangerous ones', () => {
   assert.equal(normalizeUrl(''), null);
 });
 
+test('normalizeUrl rejects markup and prose that a dot alone would let through', () => {
+  // The bulk-upload scanner splits pasted text on whitespace and offers every
+  // token as a URL, so pasting raw OPML instead of a URL list turned the markup
+  // itself into feeds. The old check was `hostname.includes('.')`, and every
+  // one of these contains a dot: ~3,700 reached production, where they are
+  // re-crawled forever and fail `blocked-host`.
+  //
+  // These are the real stored feed_urls, with the `https://` the old code added
+  // and the trailing slash `URL.toString()` gave them.
+  for (const token of [
+    'version="1.0"',   // an XML declaration
+    'text="gg.deals',  // an OPML attribute, torn at the quote
+    'title="arnika.org',
+    'zombies.)',       // a sentence ending in a word and a bracket
+    'yourself."',
+    'z.',              // a single letter and a full stop
+    'you.',
+    'york.',
+  ]) {
+    assert.equal(normalizeUrl(token), null, `${token} is not a hostname`);
+  }
+});
+
+test('normalizeUrl still accepts the unusual hosts that are real', () => {
+  // The gate rejects what cannot be a hostname, not what is merely unusual --
+  // so this is the half of the change that would break the directory if it
+  // were wrong.
+  assert.equal(normalizeUrl('sub.domain.co.uk'), 'https://sub.domain.co.uk/');
+  assert.equal(normalizeUrl('xn--bcher-kva.de'), 'https://xn--bcher-kva.de/', 'IDN arrives punycoded');
+  assert.equal(normalizeUrl('EXAMPLE.COM'), 'https://example.com/');
+  assert.equal(normalizeUrl('news.ycombinator.com/rss'), 'https://news.ycombinator.com/rss');
+  assert.equal(normalizeUrl('http://example.com:8080/feed'), 'http://example.com:8080/feed', 'a port is fine');
+  // A feed genuinely served from a dotted quad is odd but not impossible, and
+  // private ranges are refused later by isPublicHost rather than here.
+  assert.equal(normalizeUrl('192.168.1.1'), 'https://192.168.1.1/');
+  assert.equal(normalizeUrl('999.1.1.1'), null, 'but not a quad that cannot be one');
+});
+
 test('findFeedLinks reads alternate links regardless of attribute order', () => {
   const html = `
     <link rel="alternate" type="application/rss+xml" href="/feed.xml">