Versions mentioned in the description apply to the upstream
Remediation section below for
Debian:10 relevant versions.
GnuPG 2.2.4 and 2.2.5 does not enforce a configuration in which key certification requires an offline master Certify key, which results in apparently valid certifications that occurred only with access to a signing subkey.
gnupg2 to version 2.2.7-1 or higher.