Incus is a system container and virtual machine manager that supports user‑created images. Prior to version 7.3.0, any user with the non‑admin TLS/RBAC rights `can_create_images` and `can_create_instances` can supply a custom image. An image may contain a file called `backup.yaml` that is a symbolic link pointing to an arbitrary file on the host. When the root‑privileged daemon performs an instance backup, it follows that symlink and writes the backup data to the referenced host file, effectively allowing the attacker to overwrite or execute code as root. This vulnerability is classified as an OS path traversal / local file overwrite flaw (CWE‑59, CWE‑61).

The affected product is Incus by LXC. The issue exists in any release before 7.3.0; users running 7.2.x or earlier are at risk. The fix was introduced in Incus 7.3.0.

The risk is critical with a CVSS score of 9.9. No EPSS data is available, and the flaw is not listed in CISA’s KEV catalog. An attacker who can create a project‑confined Incus user with image upload rights can supply a crafted backup.yaml symlink and trigger arbitrary code execution as root on the host. The exploitation path requires legitimate access to the Incus API or CLI with the minimal permissions mentioned above; no network‑wide exposure is required beyond that access. The vulnerability is fully mitigated by upgrading to 7.3.0 or later, which removes the ability to follow symlinks during backup creation.