CVE-2026-55843: CWE-269: Improper Privilege Management in grokability snipe-it

## Impact The `update()` method in `UsersController` passes the `permission` request field unconditionally to `NormalizePermissionsPayloadAction`, which returns an empty array when the field is absent. The result is passed to `PreserveUnauthorizedPrivilegedPermissionsAction`, which selectively restores only the `superuser` key (when the editor is not a superuser) and the `admin` key (when the editor is neither admin nor superuser). All other permissions — including the `admin` flag itself when the editing user is an admin — are discarded and `$user->permissions` is overwritten with the sparse result. The `canEditAuthFields` gate permits admins to update other non-superuser accounts (including other admins). When an admin sends a `PUT /users/{id}` request for another admin without including the `permission` field, the target's `admin` flag and all granular permissions are permanently destroyed. The target loses administrative access entirely with no error, warning, or out-of-band notification. A secondary, lower-impact path exists for non-admin users holding the `users.edit` permission: they may target regular (non-admin, non-superuser) accounts and wipe all granular permissions in the same way. ### Patches Patched in https://github.com/grokability/snipe-it/commit/1cff2d67aabd00ee51d864c1d7fb717494c1d6ad