diff --git a/.env.example b/.env.example
index 2ebd111..db26eed 100644
--- a/.env.example
+++ b/.env.example
@@ -9,6 +9,7 @@ CLICKTHROUGH_GRID_COLS=12
 # CLICKTHROUGH_ALLOWED_REGION=0,0,1920,1080
 
 CLICKTHROUGH_EXEC_ENABLED=true
+CLICKTHROUGH_EXEC_SECRET=replace-with-a-strong-random-secret
 CLICKTHROUGH_EXEC_DEFAULT_SHELL=powershell
 CLICKTHROUGH_EXEC_TIMEOUT_S=30
 CLICKTHROUGH_EXEC_MAX_TIMEOUT_S=120
diff --git a/README.md b/README.md
index cfbd57e..b57fc1c 100644
--- a/README.md
+++ b/README.md
@@ -50,6 +50,7 @@ Environment variables:
 - `CLICKTHROUGH_GRID_COLS` (default `12`)
 - `CLICKTHROUGH_ALLOWED_REGION` (optional `x,y,width,height`)
 - `CLICKTHROUGH_EXEC_ENABLED` (default `true`)
+- `CLICKTHROUGH_EXEC_SECRET` (**required for `/exec` to run**)
 - `CLICKTHROUGH_EXEC_DEFAULT_SHELL` (default `powershell`; one of `powershell`, `bash`, `cmd`)
 - `CLICKTHROUGH_EXEC_TIMEOUT_S` (default `30`)
 - `CLICKTHROUGH_EXEC_MAX_TIMEOUT_S` (default `120`)
diff --git a/TODO.md b/TODO.md
index 4a326c7..a5e56aa 100644
--- a/TODO.md
+++ b/TODO.md
@@ -22,3 +22,4 @@
 - [x] Document exec API + config
 - [x] Create backlog issues for OCR/find/window/input/session-state improvements
 - [ ] Open PR for exec feature branch and review/merge
+- [x] Require configured exec secret + per-request exec secret header
diff --git a/docs/API.md b/docs/API.md
index 1c9bf7d..26b6237 100644
--- a/docs/API.md
+++ b/docs/API.md
@@ -147,6 +147,10 @@ Hotkey:
 
 Execute a shell command on the host running Clickthrough.
 
+Requirements:
+- `CLICKTHROUGH_EXEC_SECRET` must be configured on the server
+- send header `x-clickthrough-exec-secret: <secret>`
+
 ```json
 {
   "command": "Get-Process | Select-Object -First 5",
@@ -162,6 +166,7 @@ Notes:
 - if `shell` is omitted, server uses `CLICKTHROUGH_EXEC_DEFAULT_SHELL`
 - output is truncated based on `CLICKTHROUGH_EXEC_MAX_OUTPUT_CHARS`
 - endpoint can be disabled with `CLICKTHROUGH_EXEC_ENABLED=false`
+- if `CLICKTHROUGH_EXEC_SECRET` is missing, `/exec` is blocked (`403`)
 
 Response includes `stdout`, `stderr`, `exit_code`, timeout state, and execution metadata.
 
diff --git a/server/app.py b/server/app.py
index ab30f76..602fd6c 100644
--- a/server/app.py
+++ b/server/app.py
@@ -1,4 +1,5 @@
 import base64
+import hmac
 import io
 import os
 import subprocess
@@ -49,6 +50,7 @@ SETTINGS = {
     "exec_default_timeout_s": int(os.getenv("CLICKTHROUGH_EXEC_TIMEOUT_S", "30")),
     "exec_max_timeout_s": int(os.getenv("CLICKTHROUGH_EXEC_MAX_TIMEOUT_S", "120")),
     "exec_max_output_chars": int(os.getenv("CLICKTHROUGH_EXEC_MAX_OUTPUT_CHARS", "20000")),
+    "exec_secret": os.getenv("CLICKTHROUGH_EXEC_SECRET", "").strip(),
 }
 
 
@@ -299,6 +301,8 @@ def _resolve_exec_program(shell_name: str, command: str) -> list[str]:
 def _exec_command(req: ExecRequest) -> dict:
     if not SETTINGS["exec_enabled"]:
         raise HTTPException(status_code=403, detail="exec endpoint disabled")
+    if not SETTINGS["exec_secret"]:
+        raise HTTPException(status_code=403, detail="exec secret not configured")
 
     run_dry = SETTINGS["dry_run"] or req.dry_run
     shell_name = _pick_shell(req.shell)
@@ -452,6 +456,7 @@ def health(_: None = Depends(_auth)):
         "allowed_region": SETTINGS["allowed_region"],
         "exec": {
             "enabled": SETTINGS["exec_enabled"],
+            "secret_configured": bool(SETTINGS["exec_secret"]),
             "default_shell": SETTINGS["exec_default_shell"],
             "default_timeout_s": SETTINGS["exec_default_timeout_s"],
             "max_timeout_s": SETTINGS["exec_max_timeout_s"],
@@ -575,7 +580,17 @@ def action(req: ActionRequest, _: None = Depends(_auth)):
 
 
 @app.post("/exec")
-def exec_command(req: ExecRequest, _: None = Depends(_auth)):
+def exec_command(
+    req: ExecRequest,
+    x_clickthrough_exec_secret: Optional[str] = Header(default=None),
+    _: None = Depends(_auth),
+):
+    expected = SETTINGS["exec_secret"]
+    if not expected:
+        raise HTTPException(status_code=403, detail="exec secret not configured")
+    if not x_clickthrough_exec_secret or not hmac.compare_digest(x_clickthrough_exec_secret, expected):
+        raise HTTPException(status_code=401, detail="invalid exec secret")
+
     result = _exec_command(req)
     return {
         "ok": True,