Comment 3 for bug 1829055

rds is also blocked by default in ubuntu, via the /etc/modprobe.d/blacklist-rare-network.conf configuration file.

  # rds
  alias net-pf-21 off

It's also not entirely clear that this is actually remotely exploitable, as network namespace exit is normally a local action, which is what would trigger a cleanup. NVD's CVSS score (https://nvd.nist.gov/vuln/detail/CVE-2019-11815) claims the vulnerability is network accessible (which is the basis for a couple of the news articles going around), but e.g. SUSE considers it local access only (see https://www.suse.com/security/cve/CVE-2019-11815/).