fix(NODE-5200): relax SRV record validation to account for a dot suffix (#3640)

Co-authored-by: Neal Beeken <[email protected]>

Author: baileympearson

src/connection_string.ts

@@ -35,6 +35,7 @@ import {
   HostAddress,
   isRecord,
   makeClientMetadata,
+  matchesParentDomain,
   parseInteger,
   setDifference
 } from './utils';
@@ -47,21 +48,6 @@ const LB_REPLICA_SET_ERROR = 'loadBalanced option not supported with a replicaSe
 const LB_DIRECT_CONNECTION_ERROR =
   'loadBalanced option not supported when directConnection is provided';
 
-/**
- * Determines whether a provided address matches the provided parent domain in order
- * to avoid certain attack vectors.
- *
- * @param srvAddress - The address to check against a domain
- * @param parentDomain - The domain to check the provided address against
- * @returns Whether the provided address matches the parent domain
- */
-function matchesParentDomain(srvAddress: string, parentDomain: string): boolean {
-  const regex = /^.*?\./;
-  const srv = `.${srvAddress.replace(regex, '')}`;
-  const parent = `.${parentDomain.replace(regex, '')}`;
-  return srv.endsWith(parent);
-}
-
 /**
  * Lookup a `mongodb+srv` connection string, combine the parts and reparse it as a normal
  * connection string.

src/sdam/srv_polling.ts

@@ -4,22 +4,7 @@ import { clearTimeout, setTimeout } from 'timers';
 import { MongoRuntimeError } from '../error';
 import { Logger, LoggerOptions } from '../logger';
 import { TypedEventEmitter } from '../mongo_types';
-import { HostAddress } from '../utils';
-
-/**
- * Determines whether a provided address matches the provided parent domain in order
- * to avoid certain attack vectors.
- *
- * @param srvAddress - The address to check against a domain
- * @param parentDomain - The domain to check the provided address against
- * @returns Whether the provided address matches the parent domain
- */
-function matchesParentDomain(srvAddress: string, parentDomain: string): boolean {
-  const regex = /^.*?\./;
-  const srv = `.${srvAddress.replace(regex, '')}`;
-  const parent = `.${parentDomain.replace(regex, '')}`;
-  return srv.endsWith(parent);
-}
+import { HostAddress, matchesParentDomain } from '../utils';
 
 /**
  * @internal

src/utils.ts

@@ -1430,3 +1430,29 @@ export function parseUnsignedInteger(value: unknown): number | null {
 
   return parsedInt != null && parsedInt >= 0 ? parsedInt : null;
 }
+
+/**
+ * Determines whether a provided address matches the provided parent domain.
+ *
+ * If a DNS server were to become compromised SRV records would still need to
+ * advertise addresses that are under the same domain as the srvHost.
+ *
+ * @param address - The address to check against a domain
+ * @param srvHost - The domain to check the provided address against
+ * @returns Whether the provided address matches the parent domain
+ */
+export function matchesParentDomain(address: string, srvHost: string): boolean {
+  // Remove trailing dot if exists on either the resolved address or the srv hostname
+  const normalizedAddress = address.endsWith('.') ? address.slice(0, address.length - 1) : address;
+  const normalizedSrvHost = srvHost.endsWith('.') ? srvHost.slice(0, srvHost.length - 1) : srvHost;
+
+  const allCharacterBeforeFirstDot = /^.*?\./;
+  // Remove all characters before first dot
+  // Add leading dot back to string so
+  //   an srvHostDomain = '.trusted.site'
+  //   will not satisfy an addressDomain that endsWith '.fake-trusted.site'
+  const addressDomain = `.${normalizedAddress.replace(allCharacterBeforeFirstDot, '')}`;
+  const srvHostDomain = `.${normalizedSrvHost.replace(allCharacterBeforeFirstDot, '')}`;
+
+  return addressDomain.endsWith(srvHostDomain);
+}

test/unit/utils.test.ts

@@ -11,6 +11,7 @@ import {
   HostAddress,
   isHello,
   List,
+  matchesParentDomain,
   maybeCallback,
   MongoDBNamespace,
   shuffle
@@ -858,4 +859,46 @@ describe('driver utils', function () {
       it(title, () => expect(compareObjectId(oid1, oid2)).to.equal(result));
     }
   });
+
+  describe('matchesParentDomain()', () => {
+    const exampleSrvName = 'i-love-javascript.mongodb.io';
+    const exampleSrvNameWithDot = 'i-love-javascript.mongodb.io.';
+    const exampleHostNameWithoutDot = 'i-love-javascript-00.mongodb.io';
+    const exampleHostNamesWithDot = exampleHostNameWithoutDot + '.';
+    const exampleHostNamThatDoNotMatchParent = 'i-love-javascript-00.evil-mongodb.io';
+    const exampleHostNamThatDoNotMatchParentWithDot = 'i-love-javascript-00.evil-mongodb.io.';
+
+    context('when address does not match parent domain', () => {
+      it('without a trailing dot returns false', () => {
+        expect(matchesParentDomain(exampleHostNamThatDoNotMatchParent, exampleSrvName)).to.be.false;
+      });
+
+      it('with a trailing dot returns false', () => {
+        expect(matchesParentDomain(exampleHostNamThatDoNotMatchParentWithDot, exampleSrvName)).to.be
+          .false;
+      });
+    });
+
+    context('when addresses in SRV record end with a dot', () => {
+      it('accepts address since it is considered to still match the parent domain', () => {
+        expect(matchesParentDomain(exampleHostNamesWithDot, exampleSrvName)).to.be.true;
+      });
+    });
+
+    context('when SRV host ends with a dot', () => {
+      it('accepts address if it ends with a dot', () => {
+        expect(matchesParentDomain(exampleHostNamesWithDot, exampleSrvNameWithDot)).to.be.true;
+      });
+
+      it('accepts address if it does not end with a dot', () => {
+        expect(matchesParentDomain(exampleHostNameWithoutDot, exampleSrvName)).to.be.true;
+      });
+    });
+
+    context('when addresses in SRV record end without dots', () => {
+      it('accepts address since it matches the parent domain', () => {
+        expect(matchesParentDomain(exampleHostNamesWithDot, exampleSrvName)).to.be.true;
+      });
+    });
+  });
 });