[CVE-2021-22903] Possible Open Redirect Vulnerability in Action Pack

[Aaron Patterson]

There is a possible Open Redirect Vulnerability in Action Pack. This

vulnerability has been assigned the CVE identifier CVE-2021-22903.

Versions Affected:  >= v6.1.0.rc2

Not affected:       < v6.1.0.rc2

Fixed Versions:     6.1.3.2

Impact

------

This is similar to CVE-2021-22881: Specially crafted Host headers in

combination with certain "allowed host" formats can cause the Host

Authorization middleware in Action Pack to redirect users to a malicious

website.

Since rails/rails@9bc7ea5, strings in config.hosts that do not have a leading

dot are converted to regular expressions without proper escaping. This causes,

for example, config.hosts << "sub.example.com" to permit a request with a Host

header value of sub-example.com.

Releases

--------

The fixed releases are available at the normal locations.

Workarounds

-----------

The following monkey patch put in an initializer can be used as a workaround:

```ruby

class ActionDispatch::HostAuthorization::Permissions

  def sanitize_string(host)

    if host.start_with?(".")

      /\A(.+\.)?#{Regexp.escape(host[1..-1])}\z/i

    else

      /\A#{Regexp.escape host}\z/i

    end

  end

end

```

Patches

-------

To aid users who aren't able to upgrade immediately we have provided patches for

the two supported release series. They are in git-am format and consist of a

single changeset.

* 6-1-open-redirect.patch - Patch for 6.1 series

Please note that only the 6.1.Z, 6.0.Z, and 5.2.Z series are supported at

present. Users of earlier unsupported releases are advised to upgrade as soon

as possible as we cannot guarantee the continued availability of security

fixes for unsupported releases.

Credits

-------

Thanks Jonathan Hefner (https://hackerone.com/jonathanhefner) for reporting this bug!

--

Aaron Patterson
http://tenderlovemaking.com/