Index: openacs-4/packages/file-storage/www/file-add.tcl
===================================================================
RCS file: /usr/local/cvsroot/openacs-4/packages/file-storage/www/file-add.tcl,v
diff -u -r1.28.2.3 -r1.28.2.4
--- openacs-4/packages/file-storage/www/file-add.tcl	7 Jun 2021 14:00:06 -0000	1.28.2.3
+++ openacs-4/packages/file-storage/www/file-add.tcl	29 Dec 2021 17:38:20 -0000	1.28.2.4
@@ -239,6 +239,14 @@
                              -collapse_spaces \
                              -tolower \
                              $upload_file]
+        # If the sanitized upload_file name turns out empty, the file
+        # name was only made of invalid characters and chances are
+        # something funny is happening. We complain.
+        if {[string length $upload_file] == 0} {
+            template::form::set_error file-add upload_file \
+                [_ acs-tcl.lt_name_contains_invalid [list name [_ file-storage.Name]]]
+            break
+        }
 
         set existing_item_id [fs::get_item_id -name $upload_file -folder_id $folder_id]