Warning: work in progress. Incomplete
People who have been in security a long time (or even not that long) know that some inputs should be treated
as tainted. For example, environment variables from a user should not be used in a
set-uid program, inputs from a different user should be validated, etc...
Traditionally we say that the environment of a set-uid program is tainted
and
should not be used (or used with much care).
Therefore we want all set-uid/set-gid programs to treat their environment and user inputs as tainted.