diff --git a/code-interpreter/app/services/executor_kubernetes.py b/code-interpreter/app/services/executor_kubernetes.py
index c03c0ea..5247631 100644
--- a/code-interpreter/app/services/executor_kubernetes.py
+++ b/code-interpreter/app/services/executor_kubernetes.py
@@ -176,7 +176,32 @@ def _create_pod_manifest(
             ],
         )
 
+        # Use iptables in an init container to drop all outbound traffic
+        # before the main executor container starts. Since all containers
+        # in a pod share a network namespace, rules set here apply to the
+        # executor container as well. This eliminates the race condition
+        # where the pod can send network requests before the Kubernetes
+        # NetworkPolicy is enforced by the CNI.
+        iptables_script = "set -e && iptables -A OUTPUT -j DROP && ip6tables -A OUTPUT -j DROP"
+        network_lockdown_container = V1Container(
+            name="network-lockdown",
+            image=self.image,
+            command=["sh", "-c", iptables_script],
+            security_context={
+                "runAsUser": 0,
+                "runAsNonRoot": False,
+                "allowPrivilegeEscalation": False,
+                "readOnlyRootFilesystem": True,
+                "capabilities": {"drop": ["ALL"], "add": ["NET_ADMIN"]},
+            },
+            resources={
+                "limits": {"cpu": "100m", "memory": "32Mi"},
+                "requests": {"cpu": "10m", "memory": "16Mi"},
+            },
+        )
+
         spec = V1PodSpec(
+            init_containers=[network_lockdown_container],
             containers=[container],
             restart_policy="Never",
             service_account_name=self.service_account if self.service_account else None,
diff --git a/executor/Dockerfile b/executor/Dockerfile
index 6a5da28..33c03a2 100644
--- a/executor/Dockerfile
+++ b/executor/Dockerfile
@@ -6,6 +6,7 @@ RUN apt-get update \
         build-essential \
         curl \
         gfortran \
+        iptables \
         libfreetype6-dev \
         liblapack-dev \
         libopenblas-dev \