Julian Gilbey discovered that schroot, a tool allowing users to execute commands in a chroot environment, had too permissive rules on chroot or session names, allowing a denial of service on the schroot service for all users that may start a schroot session. Note that existing chroots and sessions are checked during upgrade, and an upgrade is aborted if any future invalid name is detected. Problematic session and chroots can be checked before upgrading with the following command: schroot --list --all | LC_ALL=C grep -vE "^[a-z]+:[a-zA-Z0-9][a-zA-Z0-9_.-]*$" See https://codeberg.org/shelter/reschroot/src/tag/release/reschroot-1.6.13/NEWS#L10-L41 for instructions on how to resolve such a situation.