Fixes go into the next release. Older releases are not maintained separately.
Report it privately, through GitHub's private vulnerability reporting: https://github.com/theloop-am/obsidian-skywalker/security/advisories/new.
If that is unavailable to you, open an issue asking for a private channel and leave the details out of it.
Include the theme version, the Obsidian version, the platform, and how to reproduce it. A report is reviewed before anything is disclosed publicly; when a fix is released, the advisory says who reported it unless you would rather it did not.
A theme is a stylesheet. It runs no code and reads no files. The one thing it can
do that touches the outside world is fetch a resource — a font, an image, a
stylesheet — and that is what mise run test:assets refuses: every font and image
is inside the stylesheet, and a rule that names an http, https or protocol-
relative address fails the build.
That check covers the snippets in this repository as well, because they ship here and people copy them into their vaults.
If you find a released theme.css that reaches the network, that is a security
report and the section above is how to send it.