CVE-2026-47243: Kata guest escape: runtime-rs guest-root to host-root escape via virtiofs

In the runtime-rs standalone virtio-fs path, verified here with QEMU (and verified with Cloud Hypervisor too), Kata Containers runs host virtiofsd as root with:

--sandbox none --seccomp none

If an attacker has root-equivalent execution inside the Kata guest VM, they can send raw FUSE requests directly to the host virtiofsd. With the tested runtime-rs virtio-fs configuration, a raw FUSE_SYMLINK request whose new symlink name is an absolute host path is honored outside the virtio-fs shared directory.

This lets guest root create host-root owned symlinks in sensitive host paths. The PoC created here will create symlinks in the host /etc/cron.d directory, causing host cron to execute a guest-controlled payload as host root.

Impact: guest root can execute code as host root.