CVE-2018-6954

systemd-tmpfiles en systemd, hasta 237, gestiona de manera incorrecta los vínculos simbólicos presentes en componentes de ruta no terminales. Esto permite que usuarios locales se hagan dueños de archivos arbitrarios mediante vectores relacionados con la creación de un directorio y un archivo bajo ese directorio para, posteriormente, reemplazarlo por un vínculo simbólico. Esto ocurre incluso aunque el sysctl fs.protected_symlinks esté activado.

USN-3816-1 fixed several vulnerabilities in systemd. However, the fix for CVE-2018-6954 was not sufficient. This update provides the remaining fixes. Jann Horn discovered that unit_deserialize incorrectly handled status messages above a certain length. A local attacker could potentially exploit this via NotifyAccess to inject arbitrary state across re-execution and obtain root privileges. Jann Horn discovered a race condition in chown_one. A local attacker could potentially exploit this by setting arbitrary permissions on certain files to obtain root privileges. This issue only affected Ubuntu 18.04 LTS and Ubuntu 18.10. It was discovered that systemd-tmpfiles mishandled symlinks in non-terminal path components. A local attacker could potentially exploit this by gaining ownership of certain files to obtain root privileges. This issue only affected Ubuntu 16.04 LTS and Ubuntu 18.04 LTS. Various other issues were also addressed.