fix: LiveQuery subscription with invalid regular expression crashes server ([GHSA-827p-g5x5-h86c](https://github.com/parse-community/parse-server/security/advisories/GHSA-827p-g5x5-h86c)) (#10199)

spec/ParseLiveQuery.spec.js

@@ -646,6 +646,82 @@ describe('ParseLiveQuery', function () {
     );
   });
 
+  it('rejects subscription with invalid $regex pattern', async () => {
+    await reconfigureServer({
+      liveQuery: {
+        classNames: ['TestObject'],
+      },
+      startLiveQueryServer: true,
+      verbose: false,
+      silent: true,
+    });
+
+    const query = new Parse.Query('TestObject');
+    query._where = { foo: { $regex: '[invalid' } };
+    await expectAsync(query.subscribe()).toBeRejectedWithError(/Invalid regular expression/);
+  });
+
+  it('rejects subscription with non-string $regex value', async () => {
+    await reconfigureServer({
+      liveQuery: {
+        classNames: ['TestObject'],
+      },
+      startLiveQueryServer: true,
+      verbose: false,
+      silent: true,
+    });
+
+    const query = new Parse.Query('TestObject');
+    query._where = { foo: { $regex: 123 } };
+    await expectAsync(query.subscribe()).toBeRejectedWithError(
+      /\$regex must be a string or RegExp/
+    );
+  });
+
+  it('does not crash server when subscription matching throws and other subscriptions still work', async () => {
+    const server = await reconfigureServer({
+      liveQuery: {
+        classNames: ['TestObject'],
+      },
+      startLiveQueryServer: true,
+      verbose: false,
+      silent: true,
+    });
+
+    const object = new TestObject();
+    object.set('foo', 'bar');
+    await object.save();
+
+    // Create a valid subscription
+    const validQuery = new Parse.Query('TestObject');
+    validQuery.equalTo('objectId', object.id);
+    const validSubscription = await validQuery.subscribe();
+
+    // Inject a malformed subscription directly into the LiveQuery server
+    // to bypass subscribe-time validation and test the try-catch in _onAfterSave
+    const lqServer = server.liveQueryServer;
+    const Subscription = require('../lib/LiveQuery/Subscription').Subscription;
+    const badSubscription = new Subscription('TestObject', { foo: { $regex: '[invalid' } });
+    badSubscription.addClientSubscription('fakeClientId', 'fakeRequestId');
+    const classSubscriptions = lqServer.subscriptions.get('TestObject');
+    classSubscriptions.set('bad-hash', badSubscription);
+
+    // Verify the valid subscription still receives updates despite the bad subscription
+    const updatePromise = new Promise(resolve => {
+      validSubscription.on('update', obj => {
+        expect(obj.get('foo')).toBe('baz');
+        resolve();
+      });
+    });
+
+    object.set('foo', 'baz');
+    await object.save();
+    await updatePromise;
+
+    // Clean up the injected subscription
+    classSubscriptions.delete('bad-hash');
+  });
+
   it('can handle mutate beforeSubscribe query', async done => {
     await reconfigureServer({
       liveQuery: {

spec/QueryTools.spec.js

@@ -553,6 +553,49 @@ describe('matchesQuery', function () {
     expect(config.liveQuery.regexTimeout).toBe(100);
   });
 
+  it('does not throw on invalid $regex pattern', function () {
+    const player = {
+      id: new Id('Player', 'P1'),
+      name: 'Player 1',
+    };
+
+    // Invalid regex syntax should not throw, just return false
+    const q = new Parse.Query('Player');
+    q._where = { name: { $regex: '[invalid' } };
+    expect(() => matchesQuery(player, q)).not.toThrow();
+    expect(matchesQuery(player, q)).toBe(false);
+  });
+
+  it('does not throw on invalid $regex pattern with regexTimeout enabled', function () {
+    const { setRegexTimeout } = require('../lib/LiveQuery/QueryTools');
+    setRegexTimeout(100);
+    try {
+      const player = {
+        id: new Id('Player', 'P1'),
+        name: 'Player 1',
+      };
+
+      const q = new Parse.Query('Player');
+      q._where = { name: { $regex: '[invalid' } };
+      expect(() => matchesQuery(player, q)).not.toThrow();
+      expect(matchesQuery(player, q)).toBe(false);
+    } finally {
+      setRegexTimeout(0);
+    }
+  });
+
+  it('does not throw on invalid $regex flags', function () {
+    const player = {
+      id: new Id('Player', 'P1'),
+      name: 'Player 1',
+    };
+
+    const q = new Parse.Query('Player');
+    q._where = { name: { $regex: 'valid', $options: 'xyz' } };
+    expect(() => matchesQuery(player, q)).not.toThrow();
+    expect(matchesQuery(player, q)).toBe(false);
+  });
+
   it('matches $nearSphere queries', function () {
     let q = new Parse.Query('Checkin');
     q.near('location', new Parse.GeoPoint(20, 20));

src/LiveQuery/ParseLiveQueryServer.ts

@@ -190,7 +190,13 @@ class ParseLiveQueryServer {
     }
 
     for (const subscription of classSubscriptions.values()) {
-      const isSubscriptionMatched = this._matchesSubscription(deletedParseObject, subscription);
+      let isSubscriptionMatched;
+      try {
+        isSubscriptionMatched = this._matchesSubscription(deletedParseObject, subscription);
+      } catch (e) {
+        logger.error(`Failed matching subscription for class ${className}: ${e.message}`);
+        continue;
+      }
       if (!isSubscriptionMatched) {
         continue;
       }
@@ -286,14 +292,21 @@ class ParseLiveQueryServer {
       return;
     }
     for (const subscription of classSubscriptions.values()) {
-      const isOriginalSubscriptionMatched = this._matchesSubscription(
-        originalParseObject,
-        subscription
-      );
-      const isCurrentSubscriptionMatched = this._matchesSubscription(
-        currentParseObject,
-        subscription
-      );
+      let isOriginalSubscriptionMatched;
+      let isCurrentSubscriptionMatched;
+      try {
+        isOriginalSubscriptionMatched = this._matchesSubscription(
+          originalParseObject,
+          subscription
+        );
+        isCurrentSubscriptionMatched = this._matchesSubscription(
+          currentParseObject,
+          subscription
+        );
+      } catch (e) {
+        logger.error(`Failed matching subscription for class ${className}: ${e.message}`);
+        continue;
+      }
       for (const [clientId, requestIds] of _.entries(subscription.clientRequestIds)) {
         const client = this.clients.get(clientId);
         if (typeof client === 'undefined') {
@@ -520,6 +533,53 @@ class ParseLiveQueryServer {
     });
   }
 
+  _validateQueryConstraints(where: any): void {
+    if (typeof where !== 'object' || where === null) {
+      return;
+    }
+    for (const key of Object.keys(where)) {
+      const constraint = where[key];
+      if (typeof constraint === 'object' && constraint !== null) {
+        if (constraint.$regex !== undefined) {
+          const regex = constraint.$regex;
+          const isRegExpLike =
+            regex !== null &&
+            typeof regex === 'object' &&
+            typeof regex.source === 'string' &&
+            typeof regex.flags === 'string';
+          if (typeof regex !== 'string' && !isRegExpLike) {
+            throw new Parse.Error(
+              Parse.Error.INVALID_QUERY,
+              'Invalid regular expression: $regex must be a string or RegExp'
+            );
+          }
+          const pattern = isRegExpLike ? regex.source : regex;
+          const flags = isRegExpLike ? regex.flags : constraint.$options || '';
+          try {
+            new RegExp(pattern, flags);
+          } catch (e) {
+            throw new Parse.Error(
+              Parse.Error.INVALID_QUERY,
+              `Invalid regular expression: ${e.message}`
+            );
+          }
+        }
+        for (const op of ['$or', '$and', '$nor']) {
+          if (Array.isArray(constraint[op])) {
+            constraint[op].forEach((subQuery: any) => {
+              this._validateQueryConstraints(subQuery);
+            });
+          }
+        }
+        if (Array.isArray(where[key])) {
+          where[key].forEach((subQuery: any) => {
+            this._validateQueryConstraints(subQuery);
+          });
+        }
+      }
+    }
+  }
+
   _matchesSubscription(parseObject: any, subscription: any): boolean {
     // Object is undefined or null, not match
     if (!parseObject) {
@@ -951,6 +1011,9 @@ class ParseLiveQueryServer {
         }
       }
 
+      // Validate regex patterns in the subscription query
+      this._validateQueryConstraints(request.query.where);
+
       // Get subscription from subscriptions, create one if necessary
       const subscriptionHash = queryHash(request.query);
       // Add className to subscriptions if necessary

src/LiveQuery/QueryTools.js

@@ -14,28 +14,29 @@ function setRegexTimeout(ms) {
 }
 
 function safeRegexTest(pattern, flags, input) {
-  if (!regexTimeout) {
-    var re = new RegExp(pattern, flags);
-    return re.test(input);
-  }
-  var cacheKey = flags + ':' + pattern;
-  var script = scriptCache.get(cacheKey);
-  if (!script) {
-    if (scriptCache.size >= SCRIPT_CACHE_MAX) { scriptCache.clear(); }
-    script = new vm.Script('new RegExp(pattern, flags).test(input)');
-    scriptCache.set(cacheKey, script);
-  }
-  vmContext.pattern = pattern;
-  vmContext.flags = flags;
-  vmContext.input = input;
   try {
+    if (!regexTimeout) {
+      var re = new RegExp(pattern, flags);
+      return re.test(input);
+    }
+    var cacheKey = flags + ':' + pattern;
+    var script = scriptCache.get(cacheKey);
+    if (!script) {
+      if (scriptCache.size >= SCRIPT_CACHE_MAX) { scriptCache.clear(); }
+      script = new vm.Script('new RegExp(pattern, flags).test(input)');
+      scriptCache.set(cacheKey, script);
+    }
+    vmContext.pattern = pattern;
+    vmContext.flags = flags;
+    vmContext.input = input;
     return script.runInContext(vmContext, { timeout: regexTimeout });
   } catch (e) {
     if (e.code === 'ERR_SCRIPT_EXECUTION_TIMEOUT') {
       logger.warn(`Regex timeout: pattern "${pattern}" with flags "${flags}" exceeded ${regexTimeout}ms limit`);
-      return false;
+    } else {
+      logger.warn(`Invalid regex: pattern "${pattern}" with flags "${flags}": ${e.message}`);
     }
-    throw e;
+    return false;
   }
 }