LXD Root

Local Privilege Escalation to root via default lxd group membership and the lxd-installer package on Ubuntu.

Demo runs on AWS EC2 Ubuntu Server 26.04

The bug is that Ubuntu Server 26.04's default install silently grants the primary user membership in the lxd group, a group that by LXD's trust model equals passwordless root, while presenting it as an innocuous "container management" capability. Moreover, that unprivileged user can install and set up LXD on their own, without any additional privilege, so the root-equivalent group is reachable end to end without ever touching the sudo password.

Am I affected?

A host is exposed when both are true: someone unprivileged is in the lxd group, and a root-run LXD path (an installed daemon, or the lxd-installer socket) is reachable.

Check and run poc/check-vulnerable.sh:

cd poc && chmod +x check-vulnerable.sh && ./check-vulnerable.sh

LPE PoC

cd poc && chmod +x exploit.sh && ./exploit.sh # run as an unprivileged user in the lxd group

See poc/README.md for requirements, expected output, manual reproduction, and cleanup.

Suggested mitigation

The fix is on the distro side: Ubuntu Server should not place the primary user in the lxd group by default. That group is root-equivalent, so it deserves the same explicit, understood grant as sudo, not a silent default. Requiring the sudo password before the on-demand lxd-installer runs would also close the pre-install vector, but on its own it leaves an already-installed LXD exposed.

Temporary patch

Until that lands, remove every unprivileged account from the lxd group. The change takes effect on the member's next login.

getent group lxd               # list current members
sudo gpasswd -d "$USER" lxd    # remove one member; repeat for each

Then treat lxd membership like passwordless sudo: grant it only to users you already trust with root.

Credits

• Weiming Shi (swing) — STAR Labs SG Pte. Ltd.
• n132

Disclaimer

We responsibly disclosed this issue to the Ubuntu Security team and, following their review, it was determined not to constitute a security vulnerability.

This material is provided solely for authorized security research, testing, and educational purposes. It should only be used on systems that you own or for which you have obtained explicit permission to assess. The authors assume no responsibility or liability for any misuse, damage, or consequences arising from the use of this information.