Ubuntu-specific modifications to accountsservice (in patch file debian/patches/0010-set-language.patch) caused the fallback_locale variable, pointing to static storage, to be freed, in the user_change_language_authorized_cb function. This is reachable via the SetLanguage dbus function. This is fixed in versions 0.6.55-0ubuntu12~20.04.5, 0.6.55-0ubuntu13.3, 0.6.55-0ubuntu14.1.
Exploitability
AV:LAC:HPR:LUI:NScope
S:CImpact
C:HI:HA:H7.8/CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:HOther