It was discovered that sudo misparsed network masks used in Host and Host_List stanzas. This allowed the execution of commands on hosts, where the user would not be allowed to run the specified command.
For the stable distribution (squeeze), this problem has been fixed in version 1.7.4p4-2.squeeze.3.
For the unstable distribution (sid), this problem will be fixed soon.
We recommend that you upgrade your sudo packages.