runc is a CLI tool for spawning and running containers according to the OCI specification. In versions prior to 1.3.6, 1.4.0-rc.1 through 1.4.3, and 1.5.0-rc.1 through 1.5.0-rc.3, when setting up the container rootfs, setupPtmx and setupDevSymlinks call os.Remove and os.Symlink with a filepath.Join string which allow an image with /dev as a symlink to trick runc into deleting files called ptmx on the host or creating a hardcoded set of symlinks with specific names and targets in an arbitrary pre-existing host directory. This issue is not exploitable under Docker, but affects other Linux container tooling whose higher-level runtimes are built on runc. Fixed in versions 1.3.6, 1.4.3 and 1.5.0.