diff --git a/core/engine.py b/core/engine.py
index c47512d..5dfad9b 100644
--- a/core/engine.py
+++ b/core/engine.py
@@ -19,7 +19,7 @@
 from datetime import datetime, timezone
 
 from .atomics        import get_all_techniques, get_technique, get_test
-from .executor       import execute, execute_cleanup, substitute_variables, DEFAULT_TIMEOUT
+from .executor       import execute, execute_cleanup, substitute_variables_safe, DEFAULT_TIMEOUT
 from .event_collector import collect_events, normalize_via_lognorm
 from .validator      import validate_detection, validate_events_only
 from .storage        import RunStorage
@@ -147,12 +147,12 @@ def run_test(
                     }
 
         # Substitute variables in command
-        command  = substitute_variables(
-            test["command"], input_args, test.get("input_arguments", {})
+        command  = substitute_variables_safe(
+            test["command"], input_args, test.get("input_arguments", {}), test["executor_type"]
         )
         cleanup_cmd_raw = test.get("cleanup_command")
-        cleanup_command = substitute_variables(
-            cleanup_cmd_raw, input_args, test.get("input_arguments", {})
+        cleanup_command = substitute_variables_safe(
+            cleanup_cmd_raw, input_args, test.get("input_arguments", {}), test["executor_type"]
         ) if cleanup_cmd_raw else None
 
         executed_at = datetime.utcnow().isoformat() + "Z"
diff --git a/core/executor.py b/core/executor.py
index 083717f..56dc5d4 100644
--- a/core/executor.py
+++ b/core/executor.py
@@ -15,6 +15,7 @@
 import os
 import platform
 import re
+import shlex
 import subprocess
 import time
 from dataclasses import dataclass, field
@@ -48,6 +49,50 @@ def substitute_variables(command: str, input_args: dict, test_input_defs: dict)
     return result
 
 
+def _escape_for_executor(value: object, executor_type: str) -> str:
+    """Escape user-controlled values for the target shell/interpreter."""
+    s = str(value)
+    et = (executor_type or "").lower().strip()
+
+    if et in {"bash", "sh"}:
+        return shlex.quote(s)
+
+    if et == "powershell":
+        # PowerShell single-quoted string escaping: ' -> ''
+        return "'" + s.replace("'", "''") + "'"
+
+    if et == "cmd":
+        # Conservative quoting for cmd.exe arguments.
+        return '"' + s.replace('"', '""') + '"'
+
+    # Fallback: safe POSIX-style quoting.
+    return shlex.quote(s)
+
+
+def substitute_variables_safe(
+    command: str,
+    input_args: dict,
+    test_input_defs: dict,
+    executor_type: str,
+) -> str:
+    """Replace #{variable} placeholders with safely escaped values for executor_type."""
+    result = command
+    for arg_name, arg_def in test_input_defs.items():
+        value = input_args.get(arg_name, arg_def.get("default", ""))
+        result = result.replace(f"#{{{arg_name}}}", _escape_for_executor(value, executor_type))
+
+    # Replace any remaining #{...} placeholders with escaped value or marker.
+    result = re.sub(
+        r"#\{([^}]+)\}",
+        lambda m: _escape_for_executor(
+            input_args.get(m.group(1), f"MISSING_{m.group(1)}"),
+            executor_type,
+        ),
+        result,
+    )
+    return result
+
+
 def execute(
     command:       str,
     executor_type: str,