diff --git a/changelog.d/9568-child-process-null-bytes.md b/changelog.d/9568-child-process-null-bytes.md
new file mode 100644
index 0000000000..87626eef03
--- /dev/null
+++ b/changelog.d/9568-child-process-null-bytes.md
@@ -0,0 +1,11 @@
+### Fixed
+
+- **`child_process` now rejects embedded null bytes synchronously through both
+  direct imports and CommonJS-default namespaces (#9537).** The CJS method-call
+  dispatcher bypassed codegen-only validators, so `spawn`, `spawnSync`,
+  `execFile`, and related calls handed invalid file/argument strings to the OS
+  and later reported `UNKNOWN`. Runtime entry points now validate command,
+  file, and indexed argument strings before constructing a process, and
+  OS-facing `cwd`, `argv0`, `shell`, and environment strings use Node's exact
+  `ERR_INVALID_ARG_VALUE` message, including the property name and escaped
+  received value.
diff --git a/crates/perry-runtime/src/child_process/exec.rs b/crates/perry-runtime/src/child_process/exec.rs
index f0f22016ce..adfc1ac7bc 100644
--- a/crates/perry-runtime/src/child_process/exec.rs
+++ b/crates/perry-runtime/src/child_process/exec.rs
@@ -42,6 +42,7 @@ pub extern "C" fn js_child_process_exec_sync(
         let cmd_bytes = std::slice::from_raw_parts(data_ptr, len);
         String::from_utf8_lossy(cmd_bytes).into_owned()
     };
+    validate::cp_validate_no_null_bytes("command", &cmd_str);
 
     // Execute the command using the shell, honoring `cwd`/`env` options.
     #[cfg(unix)]
@@ -92,6 +93,8 @@ pub extern "C" fn js_child_process_spawn_sync(
         let cmd_data = (cmd_ptr as *const u8).add(std::mem::size_of::<StringHeader>());
         String::from_utf8_lossy(std::slice::from_raw_parts(cmd_data, cmd_len)).into_owned()
     };
+    validate::cp_validate_no_null_bytes("file", &cmd_str);
+    unsafe { validate::cp_validate_raw_args(args_ptr as i64) };
 
     let opts_val = cp_options_from_raw_args(args_ptr as i64, options_ptr as i64);
     let mode = cp_read_output_mode(opts_val, false);
@@ -258,6 +261,7 @@ pub extern "C" fn js_child_process_exec(cmd_ptr: *const StringHeader, arg1: f64,
         let cmd_bytes = std::slice::from_raw_parts(data_ptr, len);
         String::from_utf8_lossy(cmd_bytes).into_owned()
     };
+    validate::cp_validate_no_null_bytes("command", &cmd_str);
 
     if abort_signal.is_some_and(cp_abort_signal_is_aborted) {
         let stdout_box = cp_box_output(b"", &mode);
@@ -338,6 +342,8 @@ pub extern "C" fn js_child_process_exec_file(
     };
 
     let file_str = unsafe { cp_read_string_header(file_ptr) };
+    validate::cp_validate_no_null_bytes("file", &file_str);
+    validate::cp_validate_args(args_val);
     let arg_strs = cp_args_from_value(args_val);
     // execFile defaults to utf8 (callback stdout/stderr are strings).
     let mode = cp_read_output_mode(opts_val, true);
@@ -394,6 +400,8 @@ pub extern "C" fn js_child_process_exec_file_sync(
     opts_val: f64,
 ) -> f64 {
     let file_str = unsafe { cp_read_string_header(file_ptr) };
+    validate::cp_validate_no_null_bytes("file", &file_str);
+    validate::cp_validate_args(args_val);
     let mode = cp_read_output_mode(opts_val, false);
     if file_str.is_empty() {
         return cp_box_output(b"", &mode);
@@ -483,6 +491,7 @@ fn cp_promisified_run(command: Command, cmd_str: String, opts: f64) -> f64 {
 }
 
 extern "C" fn cp_promisified_exec(_closure: *const ClosureHeader, cmd_val: f64, opts: f64) -> f64 {
+    validate::cp_validate_command(cmd_val, "command");
     let cmd = cp_value_to_string(cmd_val).unwrap_or_default();
     #[cfg(unix)]
     let mut command = {
@@ -508,6 +517,8 @@ extern "C" fn cp_promisified_exec_file(
     file_val: f64,
     args_val: f64,
 ) -> f64 {
+    validate::cp_validate_command(file_val, "file");
+    validate::cp_validate_args(args_val);
     let file = cp_value_to_string(file_val).unwrap_or_default();
     let arg_strs = cp_args_from_value(args_val);
     // The 2-arg promisify(execFile) wrapper has no options slot; resolve a bare
diff --git a/crates/perry-runtime/src/child_process/options.rs b/crates/perry-runtime/src/child_process/options.rs
index 41fe9cf91a..2fd591a54b 100644
--- a/crates/perry-runtime/src/child_process/options.rs
+++ b/crates/perry-runtime/src/child_process/options.rs
@@ -52,6 +52,7 @@ pub(crate) fn cp_apply_options(command: &mut Command, opts_val: f64) {
     }
 
     if let Some(dir) = cp_value_to_string(cp_get_field(opts_val, b"cwd")) {
+        validate::cp_validate_path_no_null_bytes("options.cwd", &dir);
         if !dir.is_empty() {
             command.current_dir(dir);
         }
@@ -72,7 +73,11 @@ pub(crate) fn cp_apply_options(command: &mut Command, opts_val: f64) {
                 if JSValue::from_bits(v.to_bits()).is_undefined() {
                     continue; // Node omits keys whose value is `undefined`.
                 }
-                command.env(&key, cp_coerce_string(v));
+                let property = format!("options.env['{key}']");
+                validate::cp_validate_no_null_bytes(&property, &key);
+                let value = cp_coerce_string(v);
+                validate::cp_validate_no_null_bytes(&property, &value);
+                command.env(&key, value);
             }
         }
     }
@@ -82,7 +87,9 @@ pub(crate) fn cp_apply_options(command: &mut Command, opts_val: f64) {
 
 pub(crate) fn cp_read_argv0(opts_val: f64) -> Option<String> {
     cp_object_ptr(opts_val)?;
-    cp_value_to_string(cp_get_field(opts_val, b"argv0"))
+    let argv0 = cp_value_to_string(cp_get_field(opts_val, b"argv0"))?;
+    validate::cp_validate_no_null_bytes("options.argv0", &argv0);
+    Some(argv0)
 }
 
 pub(crate) fn cp_read_abort_signal(opts_val: f64) -> Option<f64> {
@@ -513,7 +520,10 @@ pub(crate) fn cp_build_command(cmd: &str, args: &[String], opts_val: f64) -> Com
     let mut command = if crate::value::js_is_truthy(shell) != 0 {
         // `shell: "<path>"` picks the binary; `shell: true` uses the default.
         let shell_bin = match cp_value_to_string(shell) {
-            Some(s) if !s.is_empty() => s,
+            Some(s) if !s.is_empty() => {
+                validate::cp_validate_no_null_bytes("options.shell", &s);
+                s
+            }
             _ => cp_default_shell(),
         };
         let mut line = program.clone();
diff --git a/crates/perry-runtime/src/child_process/reactor.rs b/crates/perry-runtime/src/child_process/reactor.rs
index 9d54b0302c..65cda0298e 100644
--- a/crates/perry-runtime/src/child_process/reactor.rs
+++ b/crates/perry-runtime/src/child_process/reactor.rs
@@ -1041,6 +1041,8 @@ pub extern "C" fn js_child_process_spawn_streams(
             cp_read_arg_strings(args_ptr),
         )
     };
+    validate::cp_validate_no_null_bytes("file", &cmd_str);
+    unsafe { validate::cp_validate_raw_args(args_ptr) };
 
     // `opts_ptr` arrives as a raw (unboxed) heap pointer; re-box it so the
     // options helpers can read `cwd`/`env`/`shell`. Small values mean
diff --git a/crates/perry-runtime/src/child_process/validate.rs b/crates/perry-runtime/src/child_process/validate.rs
index d1314fb3f5..91d059fe5e 100644
--- a/crates/perry-runtime/src/child_process/validate.rs
+++ b/crates/perry-runtime/src/child_process/validate.rs
@@ -13,15 +13,82 @@
 use crate::value::JSValue;
 
 use super::{
-    cp_array_ptr, cp_get_field, cp_object_ptr, cp_signal_is_valid, cp_stdio_stream_fd,
+    cp_array_ptr, cp_box_ptr, cp_get_field, cp_object_ptr, cp_signal_is_valid, cp_stdio_stream_fd,
     cp_value_to_string,
 };
 
-fn cp_throw_null_bytes() -> ! {
-    crate::fs::validate::throw_type_error_with_code(
-        "The argument must not contain null bytes",
-        "ERR_INVALID_ARG_VALUE",
-    );
+fn cp_inspect_received_string(received: &str) -> String {
+    // Node's ERR_INVALID_ARG_VALUE uses util.inspect's string quoting: prefer
+    // a delimiter absent from the value, and escape controls/backslashes.
+    let quote = if !received.contains('\'') {
+        '\''
+    } else if !received.contains('"') {
+        '"'
+    } else if !received.contains('`') && !received.contains("${") {
+        '`'
+    } else {
+        '\''
+    };
+    let mut display = String::with_capacity(received.len() + 2);
+    display.push(quote);
+    for ch in received.chars() {
+        match ch {
+            '\0' => display.push_str("\\x00"),
+            '\x08' => display.push_str("\\b"),
+            '\x0c' => display.push_str("\\f"),
+            '\n' => display.push_str("\\n"),
+            '\r' => display.push_str("\\r"),
+            '\t' => display.push_str("\\t"),
+            '\x0b' => display.push_str("\\v"),
+            '\\' => display.push_str("\\\\"),
+            ch if ch == quote => {
+                display.push('\\');
+                display.push(ch);
+            }
+            ch if ch.is_ascii_control() => {
+                use std::fmt::Write;
+                let _ = write!(display, "\\x{:02x}", ch as u32);
+            }
+            ch => display.push(ch),
+        }
+    }
+    display.push(quote);
+    display
+}
+
+fn cp_throw_null_bytes(name: &str, received: &str, path_like: bool) -> ! {
+    let subject = if name.starts_with("options.") {
+        "property"
+    } else {
+        "argument"
+    };
+    let expected = if path_like {
+        "a string, Uint8Array, or URL without null bytes"
+    } else {
+        "a string without null bytes"
+    };
+    let display = cp_inspect_received_string(received);
+    let message = format!("The {subject} '{name}' must be {expected}. Received {display}");
+    crate::fs::validate::throw_type_error_with_code(&message, "ERR_INVALID_ARG_VALUE");
+}
+
+/// Reject a string before it crosses into `std::process::Command`. This lives
+/// in the runtime, rather than only in the direct-import lowering, so CJS
+/// namespace dispatch and future call paths cannot bypass the check. Node's
+/// `ERR_INVALID_ARG_VALUE` distinguishes top-level arguments from `options.*`
+/// properties in the message.
+pub(super) fn cp_validate_no_null_bytes(name: &str, received: &str) {
+    if received.contains('\0') {
+        cp_throw_null_bytes(name, received, false);
+    }
+}
+
+/// `options.cwd` is PathLike, so Node's expected-type clause also names
+/// Uint8Array and URL even when the received value is a string.
+pub(super) fn cp_validate_path_no_null_bytes(name: &str, received: &str) {
+    if received.contains('\0') {
+        cp_throw_null_bytes(name, received, true);
+    }
 }
 
 /// Validate a `command` / `file` argument. `value` is the original NaN-boxed
@@ -31,8 +98,8 @@ fn cp_throw_null_bytes() -> ! {
 /// message when `value` is not a string. A no-op for any string.
 pub(crate) fn cp_validate_command(value: f64, name: &str) {
     if JSValue::from_bits(value.to_bits()).is_any_string() {
-        if cp_value_to_string(value).is_some_and(|value| value.contains('\0')) {
-            cp_throw_null_bytes();
+        if let Some(received) = cp_value_to_string(value) {
+            cp_validate_no_null_bytes(name, &received);
         }
         return;
     }
@@ -48,7 +115,7 @@ pub(crate) fn cp_validate_command(value: f64, name: &str) {
 /// (arrays and plain objects), but throws `TypeError [ERR_INVALID_ARG_TYPE]`
 /// with `The "args" argument must be of type object. Received …` for a
 /// primitive such as a string, number, boolean, bigint, or symbol.
-fn cp_validate_args(value: f64) {
+pub(super) fn cp_validate_args(value: f64) {
     let jv = JSValue::from_bits(value.to_bits());
     // Node's `normalizeSpawnArguments` / `normalizeExecFileArgs` reject the
     // args slot only when it is a non-nullish *primitive* (string, number,
@@ -67,8 +134,8 @@ fn cp_validate_args(value: f64) {
         if let Some(args) = cp_array_ptr(value) {
             for i in 0..unsafe { (*args).length } {
                 let value = crate::array::js_array_get_f64(args, i);
-                if cp_value_to_string(value).is_some_and(|value| value.contains('\0')) {
-                    cp_throw_null_bytes();
+                if let Some(received) = cp_value_to_string(value) {
+                    cp_validate_no_null_bytes(&format!("args[{i}]"), &received);
                 }
             }
         }
@@ -81,6 +148,21 @@ fn cp_validate_args(value: f64) {
     crate::fs::validate::throw_type_error_with_code(&message, "ERR_INVALID_ARG_TYPE");
 }
 
+/// Validate a raw args slot after codegen/native-module dispatch has stripped
+/// its NaN-box tag. Only real heap pointers can name an args array; nullish and
+/// options-overload sentinels are intentionally ignored. Re-boxing lets the
+/// shared validator preserve the original array index in its error message.
+///
+/// # Safety
+///
+/// A non-sentinel `args_ptr` must be a runtime-managed heap pointer.
+pub(super) unsafe fn cp_validate_raw_args(args_ptr: i64) {
+    if args_ptr <= 0 || !crate::value::addr_class::is_above_handle_band(args_ptr as usize) {
+        return;
+    }
+    cp_validate_args(cp_box_ptr(args_ptr as *const u8));
+}
+
 fn cp_throw_option_type(name: &str, value: f64) -> ! {
     let message = format!(
         "The \"options.{name}\" property must be of type {}. Received {}",
diff --git a/test-files/test_gap_9537_child_process_null_bytes.ts b/test-files/test_gap_9537_child_process_null_bytes.ts
new file mode 100644
index 0000000000..910b02983f
--- /dev/null
+++ b/test-files/test_gap_9537_child_process_null_bytes.ts
@@ -0,0 +1,55 @@
+// #9537 — every child_process spelling must reject embedded null bytes
+// synchronously, before a command reaches the OS. The direct-import lowering
+// already called setup validators, but CJS-default namespace dispatch skipped
+// them and surfaced an asynchronous `UNKNOWN` spawn error instead.
+//
+// Byte-for-byte vs `node --experimental-strip-types`.
+import * as direct from "node:child_process";
+import { createRequire } from "node:module";
+
+const require = createRequire(import.meta.url);
+const cjs: any = require("child_process");
+
+function probe(label: string, run: () => any): void {
+  try {
+    const value = run();
+    // Keep the broken async-spawn path from turning the fixture's intended
+    // mismatch into an unhandled `error` event on a pre-fix binary.
+    if (value && typeof value.on === "function") value.on("error", () => {});
+    console.log(label, "NO_THROW");
+  } catch (e: any) {
+    console.log(label, "|", e.name, "|", e.code, "|", e.message);
+  }
+}
+
+// Existing direct-import path: pin the corrected Node message, including the
+// argument name, original array index, escaped received value, class and code.
+probe("direct spawn file", () => direct.spawn("/bin/tr\x00ue", []));
+probe("direct spawn args[1]", () => direct.spawn("/bin/true", ["ok", "a\x00b"]));
+probe("direct spawn escaped received", () =>
+  direct.spawn("/bin/true", ["a'\\\n\x00b"]));
+probe("direct exec command", () => direct.exec("echo\x00x", () => {}));
+probe("direct execFileSync args[1]", () =>
+  direct.execFileSync("/bin/true", ["ok", "a\x00b"]));
+
+// Regression path: fused method calls on require("child_process") route
+// through the native-module dispatcher and then the runtime entry points.
+probe("cjs spawn file", () => cjs.spawn("/bin/tr\x00ue", []));
+probe("cjs spawn args[1]", () => cjs.spawn("/bin/true", ["ok", "a\x00b"]));
+probe("cjs spawnSync args[1]", () => cjs.spawnSync("/bin/true", ["ok", "a\x00b"]));
+probe("cjs exec command", () => cjs.exec("echo\x00x", () => {}));
+probe("cjs execSync command", () => cjs.execSync("echo\x00x"));
+probe("cjs execFile args[1]", () =>
+  cjs.execFile("/bin/true", ["ok", "a\x00b"], () => {}));
+probe("cjs execFileSync file", () => cjs.execFileSync("/bin/tr\x00ue", []));
+
+// OS-facing option strings use Node's `property` wording. `cwd` is PathLike,
+// so its expected-type clause additionally names Uint8Array and URL.
+probe("cjs cwd", () => cjs.spawn("/bin/true", [], { cwd: "/tmp/a\x00b" }));
+probe("cjs argv0", () => cjs.spawn("/bin/true", [], { argv0: "a\x00b" }));
+probe("cjs shell", () => cjs.spawn("true", [], { shell: "/bin/s\x00h" }));
+probe("cjs env value", () => cjs.spawn("/bin/true", [], { env: { A: "a\x00b" } }));
+probe("cjs env undefined key", () =>
+  cjs.spawn("/bin/true", [], { env: { ["A\x00B"]: undefined } }));
+
+console.log("done");