A certificate validation issue existed when processing administrator added certificates. This issue was addressed with improved certificate validation. This issue is fixed in iOS 13.6 and iPadOS 13.6, macOS Catalina 10.15.6, tvOS 13.4.8, watchOS 6.2.8. An attacker may have been able to impersonate a trusted website using shared key material for an administrator added certificate.
https://support.apple.com/kb/HT211291
https://support.apple.com/kb/HT211290