\file_storage::unpack_reference was changed to use unserialize_array instead of unserialize in MDL-78647 (which I cannot access).

However, the docstring of unserialize_array states

 * Note: If any string (key or value) has semicolon (;) as part of the string parsing will fail.

Thus, if the filename in a reference contains a semicolon, \file_storage::unpack_reference throws a file_reference_exception. The same happens with closing curly braces ("}").

Steps to reproduce

1. Create an assignment
2. Submit a file with a semicolon in its name, e.g. "foo;bar.pdf"
3. Click "Edit submission"
4. The following error will be shown

   error/filereferenceproblem

   Debug info: Not an unserializeable value

   Error code: filereferenceproblem

   $a contents: stdClass Object

   (

   [repositoryid] =>

   [reference] => a:6:{s:9:"contextid";i:3993;s:9:"component";s:21:"assignsubmission_file";s:6:"itemid";i:1;s:8:"filearea";s:16:"submission_files";s:8:"filepath";s:1:"/";s:8:"filename";s:11:"foo;bar.pdf";}

   [referencefileid] =>

   [fileid] =>

   )

   Stack trace:

   line 1962 of /lib/filestorage/file_storage.php: file_reference_exception thrown

   line 2101 of /lib/filestorage/file_storage.php: call to file_storage::unpack_reference()

   line 790 of /lib/filelib.php: call to file_storage->search_references_count()

   line 429 of /lib/form/filemanager.php: call to file_get_drafarea_files()

   line 295 of /lib/form/filemanager.php: call to form_filemanager->__construct()

   line 192 of /lib/pear/HTML/QuickForm/Renderer/Tableless.php: call to MoodleQuickForm_filemanager->toHtml()

   line 3477 of /lib/formslib.php: call to HTML_QuickForm_Renderer_Tableless->renderElement()

   line 430 of /lib/pear/HTML/QuickForm/element.php: call to MoodleQuickForm_Renderer->renderElement()

   line 1642 of /lib/pear/HTML/QuickForm.php: call to HTML_QuickForm_element->accept()

   line 2113 of /lib/formslib.php: call to HTML_QuickForm->accept()

   line 1685 of /lib/pear/HTML/QuickForm.php: call to MoodleQuickForm->accept()

   line 445 of /lib/pear/HTML/Common.php: call to HTML_QuickForm->toHtml()

   line 1045 of /lib/formslib.php: call to HTML_Common->display()

   line 1483 of /mod/assign/classes/output/renderer.php: call to moodleform->display()

   line 141 of /mod/assign/classes/output/renderer.php: call to mod_assign\output\renderer->moodleform()

   line 495 of /lib/outputrenderers.php: call to mod_assign\output\renderer->render_assign_form()

   line 4849 of /mod/assign/locallib.php: call to plugin_renderer_base->render()

   line 660 of /mod/assign/locallib.php: call to assign->view_edit_submission_page()

   line 55 of /mod/assign/view.php: call to assign->view()