Possible DoS vulnerability in Rack

There is a possible DoS vulnerability in the multipart parser in Rack. This
vulnerability has been assigned the CVE identifier CVE-2018-16470.

Versions Affected: 2.0.4, 2.0.5
Not affected: <= 2.0.3
Fixed Versions: 2.0.6

Impact

There is a possible DoS vulnerability in the multipart parser in Rack.
Carefully crafted requests can cause the multipart parser to enter a
pathological state, causing the parser to use CPU resources disproportionate to
the request size.

Impacted code can look something like this:

Rack::Request.new(env).params

But any code that uses the multi-part parser may be vulnerable.

Rack users that have manually adjusted the buffer size in the multipart parser
may be vulnerable as well.

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

Releases

The 2.0.6 release is available at the normal locations.

Workarounds

To work around this issue, the following code can be used:

require "rack/multipart/parser"

Rack::Multipart::Parser.send :remove_const, :BUFSIZE
Rack::Multipart::Parser.const_set :BUFSIZE, 16384