html/template: improper handling of empty HTML attributes #59722
Description
Templates containing actions in unquoted HTML attributes (e.g. "attr={{.}}") executed with empty input could result in output that would have unexpected results when parsed due to HTML normalization rules. This may allow injection of arbitrary attributes into tags.
Thanks to Juho Nurminen of Mattermost for reporting this issue.
This is CVE-2023-29400 and Go issue https://go.dev/issue/59722.
/cc @golang/security and @golang/release