There is a possible DoS vulnerability in the Token Authentication logic in
Action Controller.  This vulnerability has been assigned the CVE identifier
CVE-2021-22904.

Versions Affected:  >= 4.0.0
Not affected:       < 4.0.0
Fixed Versions:     6.1.3.2, 6.0.3.7, 5.2.4.6, 5.2.6

Impact
------
Impacted code uses `authenticate_or_request_with_http_token` or
`authenticate_with_http_token` for request authentication.  Impacted code
will
look something like this:

```
class PostsController < ApplicationController
  before_action :authenticate

  private

  def authenticate
    authenticate_or_request_with_http_token do |token, options|
      # ...
    end
  end
end
```

All users running an affected release should either upgrade or use one of
the
workarounds immediately.

Releases
--------
The fixed releases are available at the normal locations.

Workarounds
-----------
The following monkey patch placed in an initializer can be used to work
around
the issue:

```ruby
module ActionController::HttpAuthentication::Token
  AUTHN_PAIR_DELIMITERS = /(?:,|;|\t)/
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.

* 5-2-http-authentication-dos.patch - Patch for 5.2 series
* 6-0-http-authentication-dos.patch - Patch for 6.0 series
* 6-1-http-authentication-dos.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
-------
Thank you to https://hackerone.com/wonda_tea_coffee for reporting this
issue!

-- 
Aaron Patterson
http://tenderlovemaking.com/