diff --git a/.jules/sentinel.md b/.jules/sentinel.md
new file mode 100644
index 0000000..1d31cae
--- /dev/null
+++ b/.jules/sentinel.md
@@ -0,0 +1,4 @@
+## 2024-05-18 - [Sandbox Environment Leakage]
+**Vulnerability:** The sandbox was leaking the host's environment variables (process.env) into the sandboxed child processes.
+**Learning:** Node's `child_process.spawn()` and `spawnSync()` default to inheriting `process.env` when the `env` option is `undefined`. This bypasses sandbox isolation if the environment object is not explicitly provided.
+**Prevention:** Always explicitly set `env: options.env ?? {}` in child process options when executing untrusted code to enforce a clean environment.
diff --git a/packages/core/src/sandbox.ts b/packages/core/src/sandbox.ts
index 1daaa7b..58bc9b3 100644
--- a/packages/core/src/sandbox.ts
+++ b/packages/core/src/sandbox.ts
@@ -42,7 +42,7 @@ export function runSandboxedNodeScript(
   try {
     const result = spawnSync(process.execPath, [scriptPath], {
       cwd: options.cwd,
-      env: options.env,
+      env: options.env ?? {},
       encoding: "utf8",
       timeout: options.timeoutMs ?? DEFAULT_CPU_TIMEOUT_MS,
       killSignal: "SIGKILL",
@@ -85,7 +85,7 @@ export function runSandboxedNodeScriptAsync(
 
     const child = spawn(process.execPath, [scriptPath], {
       cwd: options.cwd,
-      env: options.env,
+      env: options.env ?? {},
       stdio: ["ignore", "pipe", "pipe"],
     });