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.

Affected: Ubuntu:14.04:LTS: gnupg, Ubuntu:16.04:LTS: gnupg, Ubuntu:18.04:LTS: gnupg2

Marcus Brinkmann discovered that during decryption or verification, GnuPG did not properly filter out terminal sequences when reporting the original filename. An attacker could use this to specially craft a file that would cause an application parsing GnuPG output to incorrectly interpret the status of the cryptographic operation reported by GnuPG. (CVE-2018-12020)

Lance Vick discovered that GnuPG did not enforce configurations where key certification required an offline primary Certify key. An attacker with access to a signing subkey could generate certifications that appeared to be valid. This issue only affected Ubuntu 18.04 LTS. (CVE-2018-9234)