diff --git a/backend/src/sandbox/tools.py b/backend/src/sandbox/tools.py
index 4bccd82..cd6a79a 100644
--- a/backend/src/sandbox/tools.py
+++ b/backend/src/sandbox/tools.py
@@ -14,6 +14,16 @@ from src.sandbox.exceptions import (
 from src.sandbox.sandbox import Sandbox
 from src.sandbox.sandbox_provider import get_sandbox_provider
 
+_ABSOLUTE_PATH_PATTERN = re.compile(r"(?<![:\w])/(?:[^\s\"'`;&|<>()]+)")
+_LOCAL_BASH_SYSTEM_PATH_PREFIXES = (
+    "/bin/",
+    "/usr/bin/",
+    "/usr/sbin/",
+    "/sbin/",
+    "/opt/homebrew/bin/",
+    "/dev/",
+)
+
 
 def replace_virtual_path(path: str, thread_data: ThreadDataState | None) -> str:
     """Replace virtual /mnt/user-data paths with actual thread data paths.
@@ -144,6 +154,35 @@ def resolve_local_tool_path(path: str, thread_data: ThreadDataState | None) -> s
     raise PermissionError("Access denied: path traversal detected")
 
 
+def validate_local_bash_command_paths(command: str, thread_data: ThreadDataState | None) -> None:
+    """Validate absolute paths in local-sandbox bash commands.
+
+    In local mode, commands must use virtual paths under /mnt/user-data for
+    user data access. A small allowlist of common system path prefixes is kept
+    for executable and device references (e.g. /bin/sh, /dev/null).
+    """
+    if thread_data is None:
+        raise SandboxRuntimeError("Thread data not available for local sandbox")
+
+    unsafe_paths: list[str] = []
+
+    for absolute_path in _ABSOLUTE_PATH_PATTERN.findall(command):
+        if absolute_path == VIRTUAL_PATH_PREFIX or absolute_path.startswith(f"{VIRTUAL_PATH_PREFIX}/"):
+            continue
+
+        if any(
+            absolute_path == prefix.rstrip("/") or absolute_path.startswith(prefix)
+            for prefix in _LOCAL_BASH_SYSTEM_PATH_PREFIXES
+        ):
+            continue
+
+        unsafe_paths.append(absolute_path)
+
+    if unsafe_paths:
+        unsafe = ", ".join(sorted(dict.fromkeys(unsafe_paths)))
+        raise PermissionError(f"Unsafe absolute paths in command: {unsafe}. Use paths under {VIRTUAL_PATH_PREFIX}")
+
+
 def replace_virtual_paths_in_command(command: str, thread_data: ThreadDataState | None) -> str:
     """Replace all virtual /mnt/user-data paths in a command string.
 
@@ -330,12 +369,15 @@ def bash_tool(runtime: ToolRuntime[ContextT, ThreadState], description: str, com
         ensure_thread_directories_exist(runtime)
         thread_data = get_thread_data(runtime)
         if is_local_sandbox(runtime):
+            validate_local_bash_command_paths(command, thread_data)
             command = replace_virtual_paths_in_command(command, thread_data)
             output = sandbox.execute_command(command)
             return mask_local_paths_in_output(output, thread_data)
         return sandbox.execute_command(command)
     except SandboxError as e:
         return f"Error: {e}"
+    except PermissionError as e:
+        return f"Error: {e}"
     except Exception as e:
         return f"Error: Unexpected error executing command: {type(e).__name__}: {e}"
 
diff --git a/backend/tests/test_sandbox_tools_security.py b/backend/tests/test_sandbox_tools_security.py
index 0fd2fbf..651701d 100644
--- a/backend/tests/test_sandbox_tools_security.py
+++ b/backend/tests/test_sandbox_tools_security.py
@@ -7,6 +7,7 @@ from src.sandbox.tools import (
     mask_local_paths_in_output,
     replace_virtual_path,
     resolve_local_tool_path,
+    validate_local_bash_command_paths,
 )
 
 
@@ -56,3 +57,27 @@ def test_resolve_local_tool_path_rejects_path_traversal() -> None:
 
     with pytest.raises(PermissionError, match="path traversal"):
         resolve_local_tool_path(f"{VIRTUAL_PATH_PREFIX}/workspace/../../../../etc/passwd", thread_data)
+
+
+def test_validate_local_bash_command_paths_blocks_host_paths() -> None:
+    thread_data = {
+        "workspace_path": "/tmp/deer-flow/threads/t1/user-data/workspace",
+        "uploads_path": "/tmp/deer-flow/threads/t1/user-data/uploads",
+        "outputs_path": "/tmp/deer-flow/threads/t1/user-data/outputs",
+    }
+
+    with pytest.raises(PermissionError, match="Unsafe absolute paths"):
+        validate_local_bash_command_paths("cat /etc/passwd", thread_data)
+
+
+def test_validate_local_bash_command_paths_allows_virtual_and_system_paths() -> None:
+    thread_data = {
+        "workspace_path": "/tmp/deer-flow/threads/t1/user-data/workspace",
+        "uploads_path": "/tmp/deer-flow/threads/t1/user-data/uploads",
+        "outputs_path": "/tmp/deer-flow/threads/t1/user-data/outputs",
+    }
+
+    validate_local_bash_command_paths(
+        "/bin/echo ok > /mnt/user-data/workspace/out.txt && cat /dev/null",
+        thread_data,
+    )