In the context of a long-lived build server it could permanently compromise the machine, allowing an attacker to modify any other package you publish from there and maintain that access even after Rust has been fixed.
If it’s not practical to use a fresh machine/vm/container/function for each build, at least rotate them out more than once a day.
You need full repeatable control over the execution environment for hermetic builds.
I also agree rust needs to either fix mitigate this. One option you have is to disable networking on the build machine.