diff --git a/gateway/platforms/telegram.py b/gateway/platforms/telegram.py
index e91a38ac6b10..4c1b04522900 100644
--- a/gateway/platforms/telegram.py
+++ b/gateway/platforms/telegram.py
@@ -496,7 +496,9 @@ def _is_callback_user_authorized(
 
         allowed_csv = os.getenv("TELEGRAM_ALLOWED_USERS", "").strip()
         if not allowed_csv:
-            return True
+            _global_open = os.getenv("GATEWAY_ALLOW_ALL_USERS", "").lower() in ("true", "1", "yes")
+            _tg_open = os.getenv("TELEGRAM_ALLOW_ALL_USERS", "").lower() in ("true", "1", "yes")
+            return _global_open or _tg_open
         allowed_ids = {uid.strip() for uid in allowed_csv.split(",") if uid.strip()}
         return "*" in allowed_ids or normalized_user_id in allowed_ids
 
diff --git a/gateway/run.py b/gateway/run.py
index 559adae89bf0..4f28f9c5459d 100644
--- a/gateway/run.py
+++ b/gateway/run.py
@@ -3363,6 +3363,13 @@ async def start(self) -> bool:
                 "Set GATEWAY_ALLOW_ALL_USERS=true in ~/.hermes/.env to allow open access, "
                 "or configure platform allowlists (e.g., TELEGRAM_ALLOWED_USERS=your_id)."
             )
+        elif _allow_all:
+            logger.warning(
+                "SECURITY WARNING: Gateway is open to ALL users (*_ALLOW_ALL_USERS=true). "
+                "Any user who finds this bot can interact with your local agent "
+                "(filesystem, terminal, credentials). "
+                "Set TELEGRAM_ALLOWED_USERS / DISCORD_ALLOWED_USERS etc. to restrict access."
+            )
         
         # Discover Python plugins before shell hooks so plugin block
         # decisions take precedence in tie cases.  The CLI startup path
diff --git a/tests/gateway/test_telegram_auth_fail_closed.py b/tests/gateway/test_telegram_auth_fail_closed.py
new file mode 100644
index 000000000000..12836a72f1a9
--- /dev/null
+++ b/tests/gateway/test_telegram_auth_fail_closed.py
@@ -0,0 +1,42 @@
+"""Tests for Telegram _is_authorized_user failing closed when no allowlist is set."""
+
+
+def _simulate_is_authorized(user_id: str, env: dict) -> bool:
+    """Replicate the env-based auth logic from TelegramAdapter._is_authorized_user."""
+    allowed_csv = env.get("TELEGRAM_ALLOWED_USERS", "").strip()
+    if not allowed_csv:
+        _global_open = env.get("GATEWAY_ALLOW_ALL_USERS", "").lower() in ("true", "1", "yes")
+        _tg_open = env.get("TELEGRAM_ALLOW_ALL_USERS", "").lower() in ("true", "1", "yes")
+        return _global_open or _tg_open
+    allowed_ids = {uid.strip() for uid in allowed_csv.split(",") if uid.strip()}
+    return "*" in allowed_ids or user_id in allowed_ids
+
+
+class TestTelegramAuthFailClosed:
+    def test_no_allowlist_no_allow_all_denies(self):
+        result = _simulate_is_authorized("999", {})
+        assert result is False
+
+    def test_no_allowlist_gateway_allow_all_true_permits(self):
+        result = _simulate_is_authorized("999", {"GATEWAY_ALLOW_ALL_USERS": "true"})
+        assert result is True
+
+    def test_no_allowlist_telegram_allow_all_true_permits(self):
+        result = _simulate_is_authorized("999", {"TELEGRAM_ALLOW_ALL_USERS": "1"})
+        assert result is True
+
+    def test_no_allowlist_allow_all_false_string_denies(self):
+        result = _simulate_is_authorized("999", {"GATEWAY_ALLOW_ALL_USERS": "false"})
+        assert result is False
+
+    def test_known_user_in_allowlist_permits(self):
+        result = _simulate_is_authorized("123456", {"TELEGRAM_ALLOWED_USERS": "123456,789012"})
+        assert result is True
+
+    def test_unknown_user_in_allowlist_denies(self):
+        result = _simulate_is_authorized("000000", {"TELEGRAM_ALLOWED_USERS": "123456,789012"})
+        assert result is False
+
+    def test_wildcard_in_allowlist_permits_anyone(self):
+        result = _simulate_is_authorized("999999", {"TELEGRAM_ALLOWED_USERS": "*"})
+        assert result is True