Handle non-IP DNS lookup results (#957)

* Handle non-IP DNS lookup results

Ignore non-IP aliases emitted by Node-compatible DNS implementations when a lookup also returns actual IP addresses. Fail closed for alias-only results and continue checking every returned IP.

Assisted-by: Codex:gpt-5

* Apply comment: Fail on DNS failture

* Document Cloudflare Workers DNS workaround

Clarify that non-IP lookup entries are tolerated only for Workerd issue #6886 while retaining fail-closed validation, and identify the regression source in test names.

Assisted-by: Codex:gpt-5

Author: SJang1

CHANGES.md

@@ -8,6 +8,17 @@ Version 2.0.23
 
 To be released.
 
+### @fedify/vocab-runtime
+
+ -  Fixed document loaders rejecting public URLs backed by CNAMEs on
+    Cloudflare Workers.  `validatePublicUrl()` now ignores non-IP aliases
+    returned alongside DNS lookup results while continuing to validate every
+    resolved IP address, and rejects lookups that return no IP addresses.
+    [[#956], [#957] by SJang1]
+
+[#956]: https://github.com/fedify-dev/fedify/issues/956
+[#957]: https://github.com/fedify-dev/fedify/pull/957
+
 ### @fedify/cfworkers
 
  -  Fixed `WorkersMessageQueue.enqueueMany()` failing when the given messages

packages/vocab-runtime/src/url.test.ts

@@ -1,10 +1,11 @@
-import { deepStrictEqual, ok, rejects } from "node:assert";
+import { deepStrictEqual, ok, rejects, throws } from "node:assert";
 import { test } from "node:test";
 import {
   expandIPv6Address,
   isValidPublicIPv4Address,
   isValidPublicIPv6Address,
   UrlError,
+  validateLookupAddresses,
   validatePublicUrl,
 } from "./url.ts";
 
@@ -65,6 +66,32 @@ test("validatePublicUrl()", async () => {
   await validatePublicUrl("https://[64:ff9b::8.8.8.8]");
 });
 
+test("validateLookupAddresses() tolerates Cloudflare Workers CNAME entries", () => {
+  validateLookupAddresses([
+    { address: "app-host.example.net.", family: 4 },
+    { address: "93.184.216.34", family: 4 },
+    { address: "2606:2800:220:1:248:1893:25c8:1946", family: 6 },
+  ]);
+});
+
+test("validateLookupAddresses() rejects unsafe or CNAME-only Cloudflare Workers results", () => {
+  throws(
+    () =>
+      validateLookupAddresses([
+        { address: "private-host.example.net.", family: 4 },
+        { address: "127.0.0.1", family: 4 },
+      ]),
+    UrlError,
+  );
+  throws(
+    () =>
+      validateLookupAddresses([
+        { address: "app-host.example.net.", family: 4 },
+      ]),
+    UrlError,
+  );
+});
+
 test("isValidPublicIPv4Address()", () => {
   ok(isValidPublicIPv4Address("8.8.8.8")); // Google DNS
   ok(!isValidPublicIPv4Address("192.168.1.1")); // private

packages/vocab-runtime/src/url.ts

@@ -3,8 +3,8 @@ import { lookup } from "node:dns/promises";
 import { isIP } from "node:net";
 
 export class UrlError extends Error {
-  constructor(message: string) {
-    super(message);
+  constructor(message: string, options?: { cause?: unknown }) {
+    super(message, options);
     this.name = "UrlError";
   }
 }
@@ -51,12 +51,42 @@ export async function validatePublicUrl(url: string): Promise<void> {
   let addresses: LookupAddress[];
   try {
     addresses = await lookup(hostname, { all: true });
-  } catch {
-    addresses = [];
+  } catch (error) {
+    throw new UrlError("DNS lookup failed", { cause: error });
   }
-  for (const { address, family } of addresses) {
+  validateLookupAddresses(addresses);
+}
+
+/**
+ * Validates the IP addresses returned by `node:dns.lookup()`.
+ *
+ * Cloudflare Workers' `node:dns` implementation currently maps every record
+ * in a DNS-over-HTTPS `Answer` array—including CNAME records—to a
+ * `LookupAddress`, even though Node.js specifies that the `address` field must
+ * contain an IPv4 or IPv6 literal.  See:
+ * https://github.com/cloudflare/workerd/issues/6886
+ *
+ * Work around that bug by ignoring non-IP entries only when the lookup also
+ * returns at least one actual IP address.  This remains fail-closed: a result
+ * containing no IP addresses is rejected, and every returned IP address is
+ * still validated and must be public.  This workaround can be revisited once
+ * the Workerd issue is fixed in supported Cloudflare Workers runtimes.
+ *
+ * @internal
+ */
+export function validateLookupAddresses(
+  addresses: readonly LookupAddress[],
+): void {
+  let ipAddressCount = 0;
+  for (const { address } of addresses) {
+    const family = isIP(address);
+    if (family === 0) continue;
+    ipAddressCount++;
     validatePublicIpAddress(address, family);
   }
+  if (ipAddressCount === 0) {
+    throw new UrlError("DNS lookup did not return any IP address");
+  }
 }
 
 function validatePublicIpAddress(address: string, family: number): void {