diff --git a/app/main.py b/app/main.py
index 86232f6..84be412 100644
--- a/app/main.py
+++ b/app/main.py
@@ -40,6 +40,42 @@ logger = logging.getLogger("pointeuse")
 app = FastAPI(title="Décompte Horaire")
 
 
+@app.middleware("http")
+async def csrf_origin_check(request: Request, call_next):
+    """Protection CSRF stateless sur les requêtes mutatives.
+
+    Stratégie défense-en-profondeur combinée au cookie SameSite=Lax :
+    si la requête porte un header Origin ou Referer, on vérifie que son host
+    correspond à celui attendu (config.base_url si définie, sinon le Host de
+    la requête). Une requête cross-site aura un Origin différent.
+    L'absence d'Origin est tolérée (cas des clients non-navigateurs comme
+    Tasker ou curl, où SameSite=Lax suffit).
+    """
+    if request.method in ("POST", "PUT", "DELETE", "PATCH"):
+        origin = request.headers.get("origin") or request.headers.get("referer")
+        if origin:
+            try:
+                parsed = urlsplit(origin)
+            except ValueError:
+                return JSONResponse({"error": "csrf"}, status_code=403)
+            origin_host = (parsed.hostname or "").lower()
+            configured_base = (load_config().get("base_url") or "").strip()
+            if configured_base:
+                try:
+                    expected = (urlsplit(configured_base).hostname or "").lower()
+                except ValueError:
+                    expected = ""
+            else:
+                expected = (request.headers.get("host") or "").lower().split(":", 1)[0]
+            if origin_host and expected and origin_host != expected:
+                logger.warning(
+                    "CSRF: origin rejettée origin=%r host=%r path=%r",
+                    origin, request.headers.get("host"), request.url.path,
+                )
+                return JSONResponse({"error": "csrf"}, status_code=403)
+    return await call_next(request)
+
+
 @app.on_event("startup")
 async def _log_config_at_startup():
     cfg = load_config()
diff --git a/app/tests/test_security.py b/app/tests/test_security.py
index a0a4e7d..73fc356 100644
--- a/app/tests/test_security.py
+++ b/app/tests/test_security.py
@@ -337,3 +337,64 @@ def test_safe_base_url_helper_unit():
     assert "localhost" in main._safe_base_url(_FakeReq("localhost"))
     # Host sans header → None
     assert main._safe_base_url(_FakeReq("")) is None
+
+
+# ── Protection CSRF (Origin check) ────────────────────────────────────────────
+
+def test_csrf_rejects_post_with_cross_site_origin():
+    """Un POST avec Origin cross-site doit être rejeté."""
+    cookies = _login("grace")
+    r = client.post(
+        "/pointage/2026-07-17",
+        cookies=cookies,
+        data={"matin_entree": "08:00", "matin_sortie": "", "aprem_entree": "", "aprem_sortie": ""},
+        headers={"Host": "testserver", "Origin": "https://evil.attacker"},
+        follow_redirects=False,
+    )
+    assert r.status_code == 403
+    assert "csrf" in r.text.lower()
+
+
+def test_csrf_rejects_post_with_cross_site_referer():
+    """Un POST avec Referer cross-site doit aussi être rejeté."""
+    cookies = _login("heidi")
+    r = client.post(
+        "/pointage/2026-07-17",
+        cookies=cookies,
+        data={"matin_entree": "08:00", "matin_sortie": "", "aprem_entree": "", "aprem_sortie": ""},
+        headers={"Host": "testserver", "Referer": "https://evil.attacker/page"},
+        follow_redirects=False,
+    )
+    assert r.status_code == 403
+
+
+def test_csrf_accepts_post_without_origin():
+    """L'absence d'Origin (curl/Tasker) doit être tolérée (SameSite suffit)."""
+    cookies = _login("ivan")
+    r = client.post(
+        "/pointage/2026-07-17",
+        cookies=cookies,
+        data={"matin_entree": "08:00", "matin_sortie": "", "aprem_entree": "", "aprem_sortie": ""},
+        follow_redirects=False,
+    )
+    assert r.status_code == 200
+
+
+def test_csrf_accepts_post_with_matching_origin():
+    """Un POST avec Origin == Host est accepté."""
+    cookies = _login("judy")
+    r = client.post(
+        "/pointage/2026-07-17",
+        cookies=cookies,
+        data={"matin_entree": "08:00", "matin_sortie": "", "aprem_entree": "", "aprem_sortie": ""},
+        headers={"Host": "testserver", "Origin": "http://testserver"},
+        follow_redirects=False,
+    )
+    assert r.status_code == 200
+
+
+def test_csrf_accepts_get_regardless_of_origin():
+    """Les GET ne sont pas concernés par la vérification CSRF."""
+    r = client.get("/login", headers={"Origin": "https://evil.attacker"})
+    # 200 (page login) ou 302 (déjà loggué) mais pas 403
+    assert r.status_code != 403