Forgejo before 1.20.5-1 allows remote attackers to test for the existence of private user accounts by appending .rss (or another extension) to a URL.
https://forgejo.org/2023-11-release-v1-20-5-1/
https://codeberg.org/forgejo/forgejo/src/branch/forgejo/RELEASE-NOTES.md
https://codeberg.org/forgejo/forgejo/commit/d7408d8b0b04afd2a3c8e23cc908e7bd3849f34d