diff --git a/python/packages/tools/agent_framework_tools/shell/_docker.py b/python/packages/tools/agent_framework_tools/shell/_docker.py
index a5ad3814a15..20da2b78da0 100644
--- a/python/packages/tools/agent_framework_tools/shell/_docker.py
+++ b/python/packages/tools/agent_framework_tools/shell/_docker.py
@@ -463,6 +463,7 @@ async def _run_stateless(self, command: str, *, timeout: float | None) -> ShellR
         started = time.monotonic()
         proc = await asyncio.create_subprocess_exec(
             *argv,
+            stdin=asyncio.subprocess.DEVNULL,
             stdout=asyncio.subprocess.PIPE,
             stderr=asyncio.subprocess.PIPE,
         )
diff --git a/python/packages/tools/agent_framework_tools/shell/_executor.py b/python/packages/tools/agent_framework_tools/shell/_executor.py
index 446d227ae1c..e12ab7da317 100644
--- a/python/packages/tools/agent_framework_tools/shell/_executor.py
+++ b/python/packages/tools/agent_framework_tools/shell/_executor.py
@@ -60,6 +60,7 @@ async def run_stateless(
     started = time.monotonic()
     proc = await asyncio.create_subprocess_exec(
         *full_argv,
+        stdin=asyncio.subprocess.DEVNULL,
         stdout=asyncio.subprocess.PIPE,
         stderr=asyncio.subprocess.PIPE,
         cwd=workdir,
diff --git a/python/packages/tools/tests/test_docker_shell_tool.py b/python/packages/tools/tests/test_docker_shell_tool.py
index 932fdb39bb2..58a145a8894 100644
--- a/python/packages/tools/tests/test_docker_shell_tool.py
+++ b/python/packages/tools/tests/test_docker_shell_tool.py
@@ -614,3 +614,27 @@ async def test_docker_no_network_by_default():
         # busybox wget against a host that should be unreachable with --network none
         r = await shell.run("wget -q -T 2 -O- http://example.com || echo NOACCESS")
         assert "NOACCESS" in r.stdout
+
+
+async def test_run_stateless_sets_stdin_to_devnull() -> None:
+    """Regression: stateless Docker spawns must not inherit host stdin.
+
+    Without stdin=DEVNULL, `docker run -i` forwards the host's stdin into the
+    container. Combined with model-chosen commands that read stdin (e.g., `cat`),
+    this causes the same input theft/hang bug as the local tool.
+
+    This test asserts the spawn is given stdin=DEVNULL by inspecting the
+    asyncio.create_subprocess_exec call.
+    """
+    tool = DockerShellTool(mode="stateless", image="alpine:3", shell="sh")
+    proc = _FakeProcess(returncode=0, communicate_results=[(b"", b"")])
+
+    with patch(
+        "agent_framework_tools.shell._docker.asyncio.create_subprocess_exec",
+        AsyncMock(return_value=proc),
+    ) as create_proc:
+        await tool._run_stateless("echo hi", timeout=5.0)
+
+    assert create_proc.await_args is not None
+    kwargs = create_proc.await_args.kwargs
+    assert kwargs.get("stdin") == asyncio.subprocess.DEVNULL, f"Expected stdin=DEVNULL, got {kwargs.get('stdin')!r}"
diff --git a/python/packages/tools/tests/test_local_shell_tool.py b/python/packages/tools/tests/test_local_shell_tool.py
index f9dcbdf172c..24ecbaaeb3b 100644
--- a/python/packages/tools/tests/test_local_shell_tool.py
+++ b/python/packages/tools/tests/test_local_shell_tool.py
@@ -846,3 +846,55 @@ async def test_persistent_confines_workdir_by_default_powershell(tmp_path: os.Pa
         await tool.run(f"Set-Location -LiteralPath '{subdir}'")
         pwd = await tool.run("(Get-Location).Path")
         assert os.path.realpath(pwd.stdout.strip()) == os.path.realpath(str(tmp_path))
+
+
+@pytest.mark.skipif(sys.platform == "win32", reason="POSIX pipe stdin test")
+async def test_stateless_does_not_inherit_host_stdin() -> None:
+    """Regression: stateless commands must not inherit the host's stdin.
+
+    Without stdin=DEVNULL, a model-chosen command like `cat` would read from
+    the agent host's stdin. In a CLI agent, that's where the user types approval
+    prompts, so `cat` would steal input and cause either theft or a hang.
+
+    This test runs a real `cat` against a real pipe as the host's stdin and asserts:
+    1. The command gets EOF immediately (not the pipe's data)
+    2. The pipe's data is still unread by the host
+    """
+    tool = LocalShellTool(mode="stateless", approval_mode="never_require", acknowledge_unsafe=True)
+
+    # Create a pipe and write data to it: this simulates a host that has
+    # input queued on stdin (e.g., a CLI agent with pre-filled approval).
+    r, w = os.pipe()
+    # Save the original stdin so we can restore it in finally
+    original_stdin = os.dup(0)
+    try:
+        os.write(w, b"host stdin data that must not be read by the tool\n")
+        # Keep write end open while executing so cat doesn't get EOF immediately
+        # if it inherits the pipe. Only close it after subprocess completes.
+
+        # Redirect file descriptor 0 (stdin) to the pipe's read end.
+        # This makes the pipe the host process's stdin.
+        os.dup2(r, 0)
+
+        # Run `cat` through the tool. Without the fix, `cat` would read from
+        # the inherited stdin (the pipe) and block until EOF.
+        result = await tool.run("cat", timeout=1.0)
+
+        # The command should exit with code 0 and produce no output (got EOF).
+        assert result.exit_code == 0, f"cat exited with {result.exit_code}"
+        assert result.stdout == "", f"cat unexpectedly read stdin: {result.stdout!r}"
+        assert result.timed_out is False, "cat hung waiting for stdin"
+
+        # Verify the pipe's data is still unread by the host.
+        # Since stdin is still redirected to the pipe, we need to restore it first.
+        os.dup2(original_stdin, 0)
+        remaining = os.read(r, 1024)
+        assert remaining == b"host stdin data that must not be read by the tool\n", (
+            f"Host stdin was consumed: {remaining!r}"
+        )
+    finally:
+        # Restore original stdin even if execution or assertions fail
+        os.dup2(original_stdin, 0)
+        os.close(original_stdin)
+        os.close(r)
+        os.close(w)