CANONICAL has patched three critical vulnerabilities in LXD, its manager for system containers and virtual machines. CVE-2026-87799 and CVE-2026-85526 are rated CVSS 9.9, while CVE-2026-85185 is rated 9.6. The flaws can allow a low-privileged user, or a malicious migration source, to write to or delete files on the host as root. This could let one tenant compromise other workloads on a shared LXD system. The affected ranges are LXD 4.0 and later for CVE-2026-87799, and LXD 4.0.2 and later for the two btrfs issues.
CVE-2026-87799 abuses symlinks planted in migration data, causing rsync or btrfs receive to redirect later writes outside the intended volume; the advisory says optimised ZFS transfers are not affected. CVE-2026-85185 uses an unchecked btrfs subvolume path in backup and migration headers, while CVE-2026-85526 exploits path traversal in an optimised backup tarball restored to btrfs storage. Canonical’s advisories report no exploitation in the wild, although a public proof of concept has been confirmed.
Administrators should upgrade to LXD 4.0.14, 5.0.10, 5.21.8 or 6.10, or use the 6.9 build at commit `bf243da`. Until patching, access to instance and volume creation, migrations and btrfs backup imports should be restricted to trusted users and sources.