Interaction between the sks-keyserver code through 1.2.0 of the SKS keyserver network, and GnuPG through 2.2.16, makes it risky to have a GnuPG keyserver configuration line referring to a host on the SKS keyserver network. Retrieving data from this network may cause a persistent denial of service, because of a Certificate Spamming Attack.
https://twitter.com/lambdafu/status/1147162583969009664
https://support.f5.com/csp/article/K08654551?utm_source=f5support&%3Butm_medium=RSS
https://support.f5.com/csp/article/K08654551
https://lists.gnupg.org/pipermail/gnupg-announce/2019q3/000439.html
https://gist.github.com/rjhansen/67ab921ffb4084c865b3618d6955275f
http://lists.opensuse.org/opensuse-security-announce/2019-08/msg00039.html