Several security vulnerabilities have been discovered in puma, a web server for Ruby/Rack applications. These flaws may lead to information leakage due to not always closing response bodies, allowing untrusted input in a response header (HTTP Response Splitting) and thus potentially facilitating several other attacks like cross-site scripting. A poorly-behaved client could also use keepalive requests to monopolize Puma's reactor and create a denial of service attack.
For Debian 9 stretch, these problems have been fixed in version 3.6.0-1+deb9u2.
We recommend that you upgrade your puma packages.
For the detailed security status of puma please refer to its security tracker page at: https://security-tracker.debian.org/tracker/puma
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