diff --git a/backend/internal/api/handlers/import_handler_coverage_test.go b/backend/internal/api/handlers/import_handler_coverage_test.go
index 42881d79..418d487d 100644
--- a/backend/internal/api/handlers/import_handler_coverage_test.go
+++ b/backend/internal/api/handlers/import_handler_coverage_test.go
@@ -340,6 +340,11 @@ func TestCommitAndCancel_InvalidSessionUUID(t *testing.T) {
 	r.ServeHTTP(wCommit, reqCommit)
 	assert.Equal(t, http.StatusBadRequest, wCommit.Code)
 
+	wCancelMissing := httptest.NewRecorder()
+	reqCancelMissing, _ := http.NewRequest(http.MethodDelete, "/api/v1/import/cancel", http.NoBody)
+	r.ServeHTTP(wCancelMissing, reqCancelMissing)
+	assert.Equal(t, http.StatusBadRequest, wCancelMissing.Code)
+
 	wCancel := httptest.NewRecorder()
 	reqCancel, _ := http.NewRequest(http.MethodDelete, "/api/v1/import/cancel?session_uuid=.", http.NoBody)
 	r.ServeHTTP(wCancel, reqCancel)
diff --git a/backend/internal/api/handlers/json_import_handler.go b/backend/internal/api/handlers/json_import_handler.go
index 9c549680..a2ffae1b 100644
--- a/backend/internal/api/handlers/json_import_handler.go
+++ b/backend/internal/api/handlers/json_import_handler.go
@@ -310,6 +310,11 @@ func (h *JSONImportHandler) Cancel(c *gin.Context) {
 		return
 	}
 
+	if strings.TrimSpace(req.SessionUUID) == "" {
+		c.JSON(http.StatusBadRequest, gin.H{"error": "session_uuid required"})
+		return
+	}
+
 	// Clean up session if it exists
 	jsonImportSessionsMu.Lock()
 	delete(jsonImportSessions, req.SessionUUID)
diff --git a/backend/internal/api/handlers/json_import_handler_test.go b/backend/internal/api/handlers/json_import_handler_test.go
index 1ae7a230..3345dd2a 100644
--- a/backend/internal/api/handlers/json_import_handler_test.go
+++ b/backend/internal/api/handlers/json_import_handler_test.go
@@ -497,6 +497,62 @@ func TestJSONImportHandler_ConflictDetection(t *testing.T) {
 	assert.Contains(t, conflictDetails, "conflict.com")
 }
 
+func TestJSONImportHandler_Cancel_RequiresValidJSONBody(t *testing.T) {
+	db := setupJSONTestDB(t)
+	handler := NewJSONImportHandler(db)
+
+	gin.SetMode(gin.TestMode)
+	router := gin.New()
+	api := router.Group("/api/v1")
+	handler.RegisterRoutes(api)
+
+	t.Run("missing body", func(t *testing.T) {
+		req := httptest.NewRequest(http.MethodPost, "/api/v1/import/json/cancel", http.NoBody)
+		req.Header.Set("Content-Type", "application/json")
+		w := httptest.NewRecorder()
+
+		router.ServeHTTP(w, req)
+		assert.Equal(t, http.StatusBadRequest, w.Code)
+	})
+
+	t.Run("invalid json", func(t *testing.T) {
+		req := httptest.NewRequest(http.MethodPost, "/api/v1/import/json/cancel", bytes.NewBufferString("{"))
+		req.Header.Set("Content-Type", "application/json")
+		w := httptest.NewRecorder()
+
+		router.ServeHTTP(w, req)
+		assert.Equal(t, http.StatusBadRequest, w.Code)
+	})
+
+	t.Run("empty object payload", func(t *testing.T) {
+		req := httptest.NewRequest(http.MethodPost, "/api/v1/import/json/cancel", bytes.NewBufferString("{}"))
+		req.Header.Set("Content-Type", "application/json")
+		w := httptest.NewRecorder()
+
+		router.ServeHTTP(w, req)
+		assert.Equal(t, http.StatusBadRequest, w.Code)
+
+		var resp map[string]string
+		err := json.Unmarshal(w.Body.Bytes(), &resp)
+		require.NoError(t, err)
+		assert.Equal(t, "session_uuid required", resp["error"])
+	})
+
+	t.Run("missing session_uuid payload", func(t *testing.T) {
+		req := httptest.NewRequest(http.MethodPost, "/api/v1/import/json/cancel", bytes.NewBufferString(`{"foo":"bar"}`))
+		req.Header.Set("Content-Type", "application/json")
+		w := httptest.NewRecorder()
+
+		router.ServeHTTP(w, req)
+		assert.Equal(t, http.StatusBadRequest, w.Code)
+
+		var resp map[string]string
+		err := json.Unmarshal(w.Body.Bytes(), &resp)
+		require.NoError(t, err)
+		assert.Equal(t, "session_uuid required", resp["error"])
+	})
+}
+
 func TestJSONImportHandler_IsCharonFormat(t *testing.T) {
 	db := setupJSONTestDB(t)
 	handler := NewJSONImportHandler(db)