diff --git a/tools/code_execution_tool.py b/tools/code_execution_tool.py
index 19270c6fe..b2fd52acd 100644
--- a/tools/code_execution_tool.py
+++ b/tools/code_execution_tool.py
@@ -431,27 +431,57 @@ def execute_code(
         # Exception: env vars declared by loaded skills (via env_passthrough
         # registry) or explicitly allowed by the user in config.yaml
         # (terminal.env_passthrough) are passed through.
-        _SAFE_ENV_PREFIXES = ("PATH", "HOME", "USER", "LANG", "LC_", "TERM",
-                              "TMPDIR", "TMP", "TEMP", "SHELL", "LOGNAME",
-                              "XDG_", "PYTHONPATH", "VIRTUAL_ENV", "CONDA")
-        _SECRET_SUBSTRINGS = ("KEY", "TOKEN", "SECRET", "PASSWORD", "CREDENTIAL",
-                              "PASSWD", "AUTH")
+        #
+        # SECURITY FIX (V-003): Whitelist-only approach for environment variables.
+        # Only explicitly allowed environment variables are passed to child.
+        # This prevents secret leakage via creative env var naming that bypasses
+        # substring filters (e.g., MY_API_KEY_XYZ instead of API_KEY).
+        _ALLOWED_ENV_VARS = frozenset([
+            # System paths
+            "PATH", "HOME", "USER", "LOGNAME", "SHELL", 
+            "PWD", "OLDPWD", "CWD", "TMPDIR", "TMP", "TEMP",
+            # Locale
+            "LANG", "LC_ALL", "LC_CTYPE", "LC_NUMERIC", "LC_TIME",
+            "LC_COLLATE", "LC_MONETARY", "LC_MESSAGES", "LC_PAPER",
+            "LC_NAME", "LC_ADDRESS", "LC_TELEPHONE", "LC_MEASUREMENT",
+            "LC_IDENTIFICATION",
+            # Terminal
+            "TERM", "TERMINFO", "TERMINFO_DIRS", "COLORTERM",
+            # XDG
+            "XDG_CONFIG_DIRS", "XDG_CONFIG_HOME", "XDG_CACHE_HOME",
+            "XDG_DATA_DIRS", "XDG_DATA_HOME", "XDG_RUNTIME_DIR",
+            "XDG_SESSION_TYPE", "XDG_CURRENT_DESKTOP",
+            # Python
+            "PYTHONPATH", "PYTHONHOME", "PYTHONDONTWRITEBYTECODE",
+            "PYTHONUNBUFFERED", "PYTHONIOENCODING", "PYTHONNOUSERSITE",
+            "VIRTUAL_ENV", "CONDA_DEFAULT_ENV", "CONDA_PREFIX",
+            # Hermes-specific (safe only)
+            "HERMES_RPC_SOCKET", "HERMES_TIMEZONE",
+        ])
+        
+        # Prefixes that are safe to pass through
+        _ALLOWED_PREFIXES = ("LC_",)
+        
         try:
             from tools.env_passthrough import is_env_passthrough as _is_passthrough
         except Exception:
             _is_passthrough = lambda _: False  # noqa: E731
+            
         child_env = {}
         for k, v in os.environ.items():
             # Passthrough vars (skill-declared or user-configured) always pass.
             if _is_passthrough(k):
                 child_env[k] = v
                 continue
-            # Block vars with secret-like names.
-            if any(s in k.upper() for s in _SECRET_SUBSTRINGS):
-                continue
-            # Allow vars with known safe prefixes.
-            if any(k.startswith(p) for p in _SAFE_ENV_PREFIXES):
+            
+            # SECURITY: Whitelist-only approach
+            # Only allow explicitly listed env vars or allowed prefixes
+            if k in _ALLOWED_ENV_VARS:
                 child_env[k] = v
+            elif any(k.startswith(p) for p in _ALLOWED_PREFIXES):
+                child_env[k] = v
+            # All other env vars are silently dropped
+            # This prevents secret leakage via creative naming
         child_env["HERMES_RPC_SOCKET"] = sock_path
         child_env["PYTHONDONTWRITEBYTECODE"] = "1"
         # Ensure the hermes-agent root is importable in the sandbox so