Debian DSA-4247-1: Critical Timing Attack Fix in Ruby Rack Protection

A timing attack was discovered in the function for CSRF token validation
of the "Ruby rack protection" framework.

For the stable distribution (stretch), this problem has been fixed in
version 1.5.3-2+deb9u1.

We recommend that you upgrade your ruby-rack-protection packages.

For the detailed security status of ruby-rack-protection please refer to
its security tracker page at:

Further information about Debian Security Advisories, how to apply
these updates to your system and frequently asked questions can be
found at: https://www.debian.org/security/