OpenPGP data signature accepted from a signing subkey without cross-certification

{
                    "vendor": "Legion of the Bouncy Castle Inc.",
                    "product": "BC-JAVA",
                    "platforms": [
                        "all"
                    ],
                    "collectionURL": "https://www.bouncycastle.org/download/bouncy-castle-java/",
                    "packageName": "bcpg",
                    "repo": "https://github.com/bcgit/bc-java",
                    "packageURL": "pkg:maven/org.bouncycastle/bcpg-jdk18on",
                    "modules": [
                        "pg"
                    ],
                    "programFiles": [
                        "OpenPGPCertificate"
                    ],
                    "versions": [
                        {
                            "status": "affected",
                            "version": "1.81",
                            "lessThan": "1.86",
                            "versionType": "maven"
                        }
                    ],
                    "defaultStatus": "unaffected"
                }