accountsservice vulnerabilities

Ubuntu-specific language helper scripts (save-to-pam-env, update-langlist) in accountsservice before 23.13.9-8ubuntu7 treat the user-controlled LANGUAGE entry in ~/.pam_environment as trusted. The value is interpolated unescaped into a sed replacement expression, allowing an attacker to inject a sed 'e' flag and arbitrary shell commands that execute with AccountsService helper process privileges (real UID 0) via the SetLanguage D-Bus method.

An Ubuntu-specific patch to AccountsService before 23.13.9-8ubuntu7 only partially drops privileges before launching language helper scripts. It changes the effective UID/GID to the target user but leaves the real UID as 0 (root). A shell spawned by a helper script inherits ruid=0 and may reset its effective UID to root, enabling local privilege escalation.

In the accountsservice package, the systemd-homed code path for SetIconFile opens a user-supplied filename as root without the validation and privilege drop performed by the classic handler. A local attacker with a systemd-homed-managed account can read arbitrary files accessible to the accounts-daemon process.

In Ubuntu's accountsservice, there is a use-after-free vulnerability that can be exploited by an unprivileged local attacker by sending a D-Bus message to the accounts-daemon process.