An issue has been found in PowerDNS Recursor from 4.0.0 up to and including 4.1.4. A remote attacker sending a DNS query for a meta-type like OPT can lead to a zone being wrongly cached as failing DNSSEC validation. It only arises if the parent zone is signed, and all the authoritative servers for that parent zone answer with FORMERR to a query for at least one of the meta-types. As a result, subsequent queries from clients requesting DNSSEC validation will be answered with a ServFail.
Exploitability
AV:NAC:LPR:NUI:NScope
S:UImpact
C:NI:NA:L5.3/CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:LInput Validation