The vulnerability arises because crun versions before 1.28 open the container root filesystem's /dev directory without the O_NOFOLLOW flag, which prevents following symbolic links. When an OCI bundle's rootfs/dev is a symlink and the bundle configuration does not mount /dev, crun follows the symlink and creates default device nodes and standard I/O symlinks at the symlink target outside the container rootfs. This can lead to creation or replacement of files outside the container, including overwriting a pre-existing ptmx file with a forced symlink. The issue occurs during a local rootful crun replay and results in crun returning failure after these changes. Version 1.28 of crun addresses this issue by fixing the device setup behavior.

An attacker with local root privileges running crun versions prior to 1.28 can cause crun to follow symlinks outside the container root filesystem and create or overwrite device nodes and symlinks on the host filesystem. This could lead to unintended modifications of host files, including replacing critical device symlinks such as ptmx. The vulnerability does not allow privilege escalation or remote exploitation by itself but can affect system integrity when exploited locally with root access.

Upgrade crun to version 1.28 or later, where this issue is fixed. There is no indication of an official patch or temporary workaround other than upgrading. Since this is not a cloud service, remediation depends on applying the fixed version. Check the vendor's official release notes or advisories for confirmation and further guidance.