The encoding/xml package in Go versions 1.15 and earlier does not correctly preserve the semantics of directives during tokenization round-trips, which allows an attacker to craft inputs that behave in conflicting ways during different stages of processing in affected downstream applications.
https://security.netapp.com/advisory/ntap-20210129-0006/
https://github.com/mattermost/xml-roundtrip-validator/blob/master/advisories/unstable-directives.md