Maintenance tool stuck in a useless state by broken update hash error

Trying to use the maintenance tool, I am informed that:

"There is an important update available. Please select 'Update components' first"

Trying to update components, I get a hash verification error:

I see that the update is dated to 23 Sep, so this "temporary" error evidently has persisted for the entire week. The maintenance tool refuses to maintain unless updated, and the update process fails, so it is stuck in a useless state.