How to recognize CVE-2019-5418

If you get requests with values for formats like this:

Copy{:locale=>[:de], :formats=>["../../../../../../../../../../etc/services{{"], :variants=>[], :handlers=>[:erb, :builder, :raw, :ruby, :coffee, :haml]}

or fails like this:

CopyInvalid query parameters: invalid %-encoding (../../../../../../../../../etc/passwd%%0000.html)

Someone tries to exploit CVE-2019-5418 Show archive.org snapshot .
If you use the latest Rails (or latest Rails LTS) you're safe. The exact versions that fix this issue are: Rails 6.0.0.beta3, 5.2.2.1, 5.1.6.2, 5.0.7.2, 4.2.11.1, Rails LTS 3.2.22.13 and Rails LTS 2.3.18.24.