diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5102b5375c..11264ebf0d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,11 @@
+# 2.3.8 (2026-11-06)
+
+### Security
+
+* **Instance isolation**: an instance's API key could act on other instances of the same installation
+  ([#2435](https://github.com/evolution-foundation/evolution-api/issues/2435)). Every request is now bound to the
+  instance it was authenticated for. Installations that host more than one instance should upgrade.
+
 # 2.3.7 (2025-12-05)
 
 ### Features
diff --git a/package-lock.json b/package-lock.json
index c45e8fef38..82f8e1c111 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "evolution-api",
-  "version": "2.3.7",
+  "version": "2.3.8",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "evolution-api",
-      "version": "2.3.7",
+      "version": "2.3.8",
       "license": "Apache-2.0",
       "dependencies": {
         "@adiwajshing/keyed-db": "^0.2.4",
diff --git a/package.json b/package.json
index 56e32fcc8a..e7d48b8fda 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "evolution-api",
-  "version": "2.3.7",
+  "version": "2.3.8",
   "description": "Rest api for communication with WhatsApp",
   "main": "./dist/main.js",
   "type": "commonjs",
diff --git a/src/api/abstract/abstract.router.ts b/src/api/abstract/abstract.router.ts
index e8449a8c8a..6287d858f4 100644
--- a/src/api/abstract/abstract.router.ts
+++ b/src/api/abstract/abstract.router.ts
@@ -17,6 +17,21 @@ type DataValidate<T> = {
 
 const logger = new Logger('Validate');
 
+const PROTECTED_INSTANCE_FIELDS = ['instanceName', 'instanceId'] as const;
+
+function sanitizeUntrustedInput(source: Record<string, any> | undefined): Record<string, any> {
+  if (!source || typeof source !== 'object') return {};
+  const sanitized: Record<string, any> = {};
+  for (const [key, value] of Object.entries(source)) {
+    if ((PROTECTED_INSTANCE_FIELDS as readonly string[]).includes(key)) {
+      logger.warn(`Ignoring attempt to override protected field "${key}" via untrusted input`);
+      continue;
+    }
+    sanitized[key] = value;
+  }
+  return sanitized;
+}
+
 export abstract class RouterBroker {
   constructor() {}
   public routerPath(path: string, param = true) {
@@ -34,9 +49,11 @@ export abstract class RouterBroker {
     const instance = request.params as unknown as InstanceDto;
 
     if (request?.query && Object.keys(request.query).length > 0) {
-      Object.assign(instance, request.query);
+      Object.assign(instance, sanitizeUntrustedInput(request.query as Record<string, any>));
     }
 
+    // Create has no :instanceName in the path and only passes the guard with the
+    // global key, so the body is where the new instance's name legitimately comes from.
     if (request.originalUrl.includes('/instance/create')) {
       Object.assign(instance, body);
     }