diff --git a/application/src/test/java/org/thingsboard/server/controller/RuleChainControllerTest.java b/application/src/test/java/org/thingsboard/server/controller/RuleChainControllerTest.java
index f8cd8e0f33..a485c02bb8 100644
--- a/application/src/test/java/org/thingsboard/server/controller/RuleChainControllerTest.java
+++ b/application/src/test/java/org/thingsboard/server/controller/RuleChainControllerTest.java
@@ -405,4 +405,21 @@ public class RuleChainControllerTest extends AbstractControllerTest {
         return doPost("/api/ruleChain", ruleChain, RuleChain.class);
     }
 
+    @Test
+    public void testScriptForbiddenForCustomer() throws Exception {
+        loginCustomerUser();
+
+        doPost("/api/ruleChain/testScript", (Object) """
+                {
+                  "script": "return msg;",
+                  "scriptType": "update",
+                  "argNames": ["msg", "metadata", "msgType"],
+                  "msg": "{}",
+                  "metadata": {},
+                  "msgType": "POST_TELEMETRY_REQUEST"
+                }
+                """)
+                .andExpect(status().isForbidden());
+    }
+
 }
diff --git a/msa/black-box-tests/src/test/java/org/thingsboard/server/msa/TestRestClient.java b/msa/black-box-tests/src/test/java/org/thingsboard/server/msa/TestRestClient.java
index 7b2cfc68d9..1e14dbd70b 100644
--- a/msa/black-box-tests/src/test/java/org/thingsboard/server/msa/TestRestClient.java
+++ b/msa/black-box-tests/src/test/java/org/thingsboard/server/msa/TestRestClient.java
@@ -328,6 +328,16 @@ public class TestRestClient {
                 .statusCode(HTTP_OK);
     }
 
+    public JsonNode testRuleChainScript(Object body) {
+        return given().spec(requestSpec)
+                .body(body)
+                .post("/api/ruleChain/testScript")
+                .then()
+                .statusCode(HTTP_OK)
+                .extract()
+                .as(JsonNode.class);
+    }
+
     private String getUrlParams(PageLink pageLink) {
         String urlParams = "pageSize={pageSize}&page={page}";
         if (!isEmpty(pageLink.getTextSearch())) {
diff --git a/msa/black-box-tests/src/test/java/org/thingsboard/server/msa/security/JsExecutorSandboxIsolationTest.java b/msa/black-box-tests/src/test/java/org/thingsboard/server/msa/security/JsExecutorSandboxIsolationTest.java
new file mode 100644
index 0000000000..1328382c5d
--- /dev/null
+++ b/msa/black-box-tests/src/test/java/org/thingsboard/server/msa/security/JsExecutorSandboxIsolationTest.java
@@ -0,0 +1,73 @@
+/**
+ * Copyright © 2016-2026 The Thingsboard Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.thingsboard.server.msa.security;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import org.testng.annotations.AfterClass;
+import org.testng.annotations.BeforeClass;
+import org.testng.annotations.Test;
+import org.thingsboard.server.msa.AbstractContainerTest;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class JsExecutorSandboxIsolationTest extends AbstractContainerTest {
+
+    @BeforeClass
+    public void beforeClass() {
+        testRestClient.login("tenant@thingsboard.org", "tenant");
+    }
+
+    @AfterClass
+    public void afterClass() {
+        testRestClient.resetToken();
+    }
+
+    /**
+     * Black-box regression for JVN#16937365: a tenant admin must not be able
+     * to escape the tb-js-executor sandbox via the host-realm prototype chain
+     * exposed through the script's `args` argument. Runs against the live
+     * docker-compose deployment, which uses script.use_sandbox=true and
+     * JS_EVALUATOR=remote (Kafka -> tb-js-executor).
+     */
+    @Test
+    public void testRuleChainScriptCannotReachHostProcess() {
+        JsonNode response = testRestClient.testRuleChainScript("""
+                {
+                  "script": "var F = args.constructor.constructor; var p = F('return process')(); return { reachedHost: !!(p && p.mainModule) };",
+                  "scriptType": "update",
+                  "argNames": ["msg", "metadata", "msgType"],
+                  "msg": "{}",
+                  "metadata": {},
+                  "msgType": "POST_TELEMETRY_REQUEST"
+                }
+                """);
+
+        // The sandboxed run must reject the escape attempt: the host `process`
+        // global is not defined inside the sandbox realm, so executing the
+        // synthesized function `F("return process")` throws.
+        assertThat(response.has("error")).isTrue();
+        String error = response.get("error").asText();
+        assertThat(error)
+                .as("sandbox must block host-realm reach via args.constructor.constructor; full error: %s", error)
+                .contains("process is not defined");
+
+        // Defense in depth: even if the script somehow returned, output must
+        // not indicate that the host process was reached.
+        if (response.hasNonNull("output")) {
+            assertThat(response.get("output").asText()).doesNotContain("\"reachedHost\":true");
+        }
+    }
+}
diff --git a/msa/black-box-tests/src/test/resources/connectivity.xml b/msa/black-box-tests/src/test/resources/connectivity.xml
index a1cbaf4af6..7cd96bb429 100644
--- a/msa/black-box-tests/src/test/resources/connectivity.xml
+++ b/msa/black-box-tests/src/test/resources/connectivity.xml
@@ -25,6 +25,7 @@
             <package name="org.thingsboard.server.msa.edqs"/>
             <package name="org.thingsboard.server.msa.cf"/>
             <package name="org.thingsboard.server.msa.rule.node"/>
+            <package name="org.thingsboard.server.msa.security"/>
         </packages>
     </test>
 </suite>
\ No newline at end of file