Understanding and Fixing Media File Upload and Deletion Issues with User Roles

Managing user roles and capabilities is a core part of WordPress administration, but it can sometimes lead to unexpected behavior. A common issue reported by users involves conflicts with the delete_users capability blocking PDF or large file uploads, and confusion over which capabilities are required to delete items from the media library. This guide explains why these problems occur and provides clear solutions.

The Problem: Unexpected Media Upload Errors and Deletion Restrictions

Users have encountered two primary issues:

1. Upload Errors with delete_users Enabled: When the delete_users capability is enabled for a role, it can sometimes cause the server to return an "Unexpected response from the server" error during media uploads, particularly for PDFs or larger files. This is counterintuitive, as these capabilities seem unrelated.
2. Inability to Delete Media Files: Users with roles like Author, Contributor, or custom roles often find they cannot delete their own or others' media files from the library, even when they believe they have the correct permissions.

Why This Happens

The root cause of these issues lies in how WordPress core and other plugins check for capabilities, often in indirect ways.

• The delete_users Upload Conflict: While WordPress core does not use the delete_users capability to check upload permissions, the function is_super_admin() uses it to define a Super Admin on a single site. Some security or admin plugins might indirectly use this function or capability check in a way that interferes with the upload process, causing a server-side error.
• Media Deletion Permissions: By default, WordPress ties the permission to delete a media file (an "attachment" post type) to the permissions for the post it is attached to. To delete a media file, a user generally needs:
  • delete_posts (to delete their own files)
  • delete_others_posts (to delete files uploaded by other users)
  • edit_posts or similar capabilities are also often involved in these checks.
  The media library interface performs additional checks that rely on these broader post capabilities.

Common Solutions

1. Fixing the delete_users Upload Conflict

If enabling delete_users is causing upload errors, the conflict is likely with another plugin.

1. Conflict Test: Deactivate all plugins except User Role Editor. Try to reproduce the upload error. If it is resolved, reactivate your plugins one-by-one to identify which one is causing the conflict.
2. Check Plugin Settings: Investigate the settings of your security, admin, or membership plugins for any options that might link user deletion rights to other administrative functions.
3. Alternative: If the delete_users capability is not essential for the role in question, consider leaving it disabled. The core capabilities needed for uploading files are upload_files and edit_posts.

2. Granting Permissions to Delete Media Files

To allow a user role to delete from the media library, you need to ensure they have the correct set of capabilities.

1. Delete Their Own Media: For a user to delete their own uploaded files, ensure the role has the delete_posts capability.
2. Delete Anyone's Media: For a user to delete any file in the library (files uploaded by other users), the role must have the delete_others_posts capability.
3. Verify Other Capabilities: Some workflows may also require edit_posts or edit_others_posts. If you are managing a custom post type, ensure its specific delete capabilities (e.g., delete_partners) are also granted.

Example for an Author role: To allow authors to delete their own media, confirm they have upload_files, edit_posts, and delete_posts.

Conclusion

Capability conflicts often arise from the complex interplay between WordPress core, themes, and plugins. The key to resolving upload and deletion issues is a methodical approach: ensure the role has the necessary core capabilities and then perform conflict testing to rule out other plugins. Understanding that media deletion is tied to post deletion permissions is the first step to unlocking the right settings for your user roles.