In libzypp before August 2018 GPG keys attached to YUM repositories were not correctly pinned, allowing malicious repository mirrors to silently downgrade to unsigned repositories with potential malicious content.
A protocol or its implementation supports interaction between multiple actors and allows those actors to negotiate which algorithm should be used as a protection mechanism such as encryption or authentication, but it does not select the strongest algorithm that is available to both parties.
The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.