[CVE-2021-22902] Possible Denial of Service vulnerability in Action Dispatch

[Aaron Patterson]

There is a possible Denial of Service vulnerability in the Mime type parser of

Action Dispatch. This vulnerability has been assigned the CVE identifier

CVE-2021-22902.

Versions Affected:  >= 6.0.0

Not affected:       < 6.0.0

Fixed Versions:     6.0.3.7, 6.1.0.2

Impact

------

There is a possible Denial of Service vulnerability in Action Dispatch.

Carefully crafted Accept headers can cause the mime type parser in Action

Dispatch to do catastrophic backtracking in the regular expression engine.

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 Mime

  class Type

    MIME_REGEXP = /\A(?:\*\/\*|#{MIME_NAME}\/(?:\*|#{MIME_NAME})(?>\s*#{MIME_PARAMETER}\s*)*)\z/

  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.

* 6-0-Prevent-catastrophic-backtracking-during-mime-parsin.patch - Patch for 6.0 series

* 6-1-Prevent-catastrophic-backtracking-during-mime-parsin.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 to Security Curious <security...@pm.me> for reporting this!

--

Aaron Patterson
http://tenderlovemaking.com/