Issue #16131 has been updated by jeremyevans0 (Jeremy Evans).


I've expanded my pull request to deprecate taint/trust and related methods with verbose warnings, and make the methods no-ops.  I believe this implements matz's plan for Ruby 2.7.

The changes involved removing tainting from all included libraries, which includes libraries such as rubygems, bundler, and json, that may want to support older versions of ruby upstream (and may need to keep taint code to work correctly in older ruby versions).  I'm not sure how we want to handle this, and I'm open to ideas.

----------------------------------------
Feature #16131: Remove $SAFE, taint and trust
https://bugs.ruby-lang.org/issues/16131#change-81708

* Author: naruse (Yui NARUSE)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
Ruby had Taint checking which is originally introduced in Perl.
https://en.wikipedia.org/wiki/Taint_checking

It was intended to provide a useful tool for handle objects which are come from outside.
Input data is set as tainted by default and call untaint if you checked or filtered the value.
Some people used this feature in the age of CGI.

But these days, no one use the mechanism and input libraries usually doesn't support it.
For example rack, as following shows its input is not tainted and the mechanism is unusable.

```
% cat foo.ru
run ->(env) do
  ['200', {'Content-Type' => 'text/plain'}, ["Is QUERY_STRING tainted?: #{env["QUERY_STRING"].tainted?}"]]
end
% rackup foo.ru
[51724] Puma starting in cluster mode...
[51724] * Version 3.12.1 (ruby 2.6.3-p62), codename: Llamas in Pajamas
[51724] * Min threads: 3, max threads: 3
[51724] * Environment: development
[51724] * Process workers: 1
[51724] * Preloading application
[51724] * Listening on tcp://localhost:9292
[51724] Use Ctrl-C to stop
[51737] + Gemfile in context: /Users/naruse/work/td-cdp-api/Gemfile
[51724] - Worker 0 (pid: 51737) booted, phase: 0
```

```
% curl http://localhost:9292/\?foo=1
Is QUERY_STRING tainted?: false
```

Therefore I think Taint checking mechanism is unusable on the current Ruby ecosystem.

On the other hand we experienced multiple vulnerability around $SAFE and taint mechanism.
https://cse.google.com/cse?q=taint&cx=008288045305770251182%3Afvruzsaknew&ie=UTF-8
The cost of maintaining it is expensive.

In conclusion, I think the taint mechanism is too expensive to maintain for the merit of it.
I suggest to remove it.



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