There was a possible directory traversal vulnerability in the Rack::Directory app that is bundled with Rack.

If certain directories exist in a director that is managed by `Rack::Directory`, an attacker could, using this vulnerability, read the contents of files on the server that were outside of the root specified in the Rack::Directory initializer.

For Debian 8 Jessie, this problem has been fixed in version 1.5.2-3+deb8u3.

We recommend that you upgrade your ruby-rack packages.

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