init_tmp in TeeJee.FileSystem.vala in Timeshift before 20.03 unsafely reuses a preexisting temporary directory in the predictable location /tmp/timeshift. It follows symlinks in this location or uses directories owned by unprivileged users. Because Timeshift also executes scripts under this location, an attacker can attempt to win a race condition to replace scripts created by Timeshift with attacker-controlled scripts. Upon success, an attacker-controlled script is executed with full root privileges. This logic is practically always triggered when Timeshift runs regardless of the command-line arguments used.

References

• https://nvd.nist.gov/vuln/detail/CVE-2020-10174
• teejee2008/timeshift@335b3d5
• https://bugzilla.suse.com/show_bug.cgi?id=1165802
• https://github.com/teejee2008/timeshift/releases/tag/v20.03
• https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/AAOFXT64CEUMJE3723JDJWTEQWQUCYMD/
• https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/SXDEPC52G46U6I7GLQNFLZXVSM7V2HYY/
• https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/TXXYQFSZ5P6ZMNFIDBAQKBFZIR2T7ZLL/
• https://usn.ubuntu.com/4312-1/
• http://www.openwall.com/lists/oss-security/2020/03/06/3