Comment 1 for bug 220843

Workaround:
I'd previously enabled root account so I was able to regain full control over system quite easily via su which does not suffers from issue:

sk@ath64:~$ su
Password:
root@ath64:/home/sk# echo 127.0.0.1 ath64 >> /etc/hosts

This has helped and now sudo resumed operation.

However please note:
- Usual user does not has root account enabled so I guess the only way in such case is to boot from CD and mount partition.Not what I'm calling easy.
- This bug leads to inabilty of updating system or configuring lots of things.

Generally, "average Joe" user probably will think his system is done.