Claws crashes with heap corruption or an access violation when unloading the RSSyl plugin, depending on the configuration. rssyl_destroy_folder() calls folder_local_destroy_folder() on the Folder* parameter, which doesn't appear to be a LocalFolder. With appverifier enabled, the Folder is allocated at the end of a page with an unmapped page immediately following. Casting it to a LocalFolder and accessing rootpath crosses into the unmapped page. The crash happens in folder_local_folder_destroy() either when trying to access the rootpath member, or shortly afterwards when freeing it. Backtrace: # Call Site 00 claws_mail!folder_local_folder_destroy+0x45 [..\..\claws-mail-3.17.8\src\localfolder.c @ 38] 01 rssyl!rssyl_destroy_folder+0x15 [..\..\..\..\claws-mail-3.17.8\src\plugins\rssyl\rssyl.c @ 263] 02 claws_mail!folder_destroy+0xa2 [..\..\claws-mail-3.17.8\src\folder.c @ 279] 03 claws_mail!folder_unregister_class+0xc7 [..\..\claws-mail-3.17.8\src\folder.c @ 165] 04 rssyl!rssyl_done+0x4d [..\..\..\..\claws-mail-3.17.8\src\plugins\rssyl\rssyl.c @ 177] 05 rssyl!plugin_done+0xd [..\..\..\..\claws-mail-3.17.8\src\plugins\rssyl\plugin.c @ 55] 06 claws_mail!plugin_unload+0x74 [..\..\..\claws-mail-3.17.8\src\common\plugin.c @ 547] 07 claws_mail!unload_cb+0x68 [..\..\..\claws-mail-3.17.8\src\gtk\pluginwindow.c @ 190] 08 libgobject_2_0_0!g_closure_invoke+0x183 09 libgobject_2_0_0!g_signal_handler_disconnect+0x11d5 0a libgobject_2_0_0!g_signal_emit_valist+0x94d 0b libgobject_2_0_0!g_signal_emit+0x18 0c libgtk_win32_2_0_0!gtk_button_clicked+0x205 0d libgobject_2_0_0!g_closure_invoke+0x183 0e libgobject_2_0_0!g_signal_handler_disconnect+0x1333 0f libgobject_2_0_0!g_signal_emit_valist+0x94d 10 libgobject_2_0_0!g_signal_emit+0x18 11 libgtk_win32_2_0_0!gtk_button_released+0x89 12 libgtk_win32_2_0_0!gtk_marshal_VOID__UINT_STRING+0x117 13 libgobject_2_0_0!g_closure_invoke+0x183 14 libgobject_2_0_0!g_signal_handler_disconnect+0x93c 15 libgobject_2_0_0!g_signal_emit_valist+0x65f 16 libgobject_2_0_0!g_signal_emit+0x18 17 libgtk_win32_2_0_0!gtk_widget_translate_coordinates+0x4ed 18 libgtk_win32_2_0_0!gtk_propagate_event+0xa1 19 libgtk_win32_2_0_0!gtk_main_do_event+0x2ab 1a libgdk_win32_2_0_0!gdk_win32_drawable_get_handle+0xcda 1b libglib_2_0_0!g_main_context_dispatch+0x253 1c libglib_2_0_0!g_main_context_dispatch+0x458 1d libglib_2_0_0!g_main_loop_run+0x74 1e libgtk_win32_2_0_0!gtk_main+0xa0 1f claws_mail!main+0x151e [..\..\claws-mail-3.17.8\src\main.c @ 1666] 20 claws_mail!__tmainCRTStartup+0x247 [.\mingw-w64-crt\crt\crtexe.c @ 341] 21 claws_mail!WinMainCRTStartup+0x1b [.\mingw-w64-crt\crt\crtexe.c @ 197] 22 KERNEL32!BaseThreadInitThunk+0x14 23 ntdll!RtlUserThreadStart+0x21