The multi-user installer in Nix before 2.35.3 sets the ownership of store contents to the user (who invoked the installer) even though it should be root ownership.
https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-100808
https://discourse.nixos.org/t/security-advisory-for-nix-and-lix-october-2026/80547