Information Exposure with Puma when used with Rails

Impact

Prior to puma version 5.6.2, puma may not always call
close on the response body. Rails, prior to version 7.0.2.2, depended on the
response body being closed in order for its CurrentAttributes implementation to
work correctly.

From Rails:

> Under certain circumstances response bodies will not be closed, for example
> a bug in a webserver[1] or a bug in a Rack middleware. In the event a
> response is not notified of a close, ActionDispatch::Executor will not know
> to reset thread local state for the next request. This can lead to data
> being leaked to subsequent requests, especially when interacting with
> ActiveSupport::CurrentAttributes.

The combination of these two behaviors (Puma not closing the body + Rails’
Executor implementation) causes information leakage.

Patches

This problem is fixed in Puma versions 5.6.2 and 4.3.11.

This problem is fixed in Rails versions 7.02.2, 6.1.4.6, 6.0.4.6, and 5.2.6.2.

See: https://github.com/advisories/GHSA-wh98-p28r-vrc9
for details about the rails vulnerability

Upgrading to a patched Rails or Puma version fixes the vulnerability.

Workarounds

Upgrade to Rails versions 7.0.2.2, 6.1.4.6, 6.0.4.6, and 5.2.6.2.

The Rails CVE
includes a middleware that can be used instead.