When sudo is configured to allow a user to edit files under a
directory that they can already write to without using sudo, they can
actually edit (read and write) arbitrary files. Daniel Svartman
reported that a configuration like this might be introduced
unintentionally if the editable files are specified using wildcards,
for example:
operator ALL=(root) sudoedit /home/\*/\*/test.txt
The default behaviour of sudo has been changed so that it does not
allow editing of a file in a directory that the user can write to, or
that is reached by following a symlink in a directory that the user
can write to. These restrictions can be disabled, but this is
strongly discouraged.
For the oldoldstable distribution (squeeze), this has been fixed in
version 1.7.4p4-2.squeeze.6.
For the oldstable distribution (wheezy) and the stable distribution
(jessie), this will be fixed soon.