We just released security patches for versions 4.1, 4.2, and nightly. If you are using nightly, you can upgrade to nightly.2024-05-31-security. We strongly suggest you upgrade to one of those versions.
@MastodonEngineering thank you!
for anyone else looking for the new version number and the link, it's 4.2.9 and https://github.com/mastodon/mastodon/releases/tag/v4.2.9 :)