Critical LXD Flaws Let Users Write to Hosts as Root

Canonical has patched three critical vulnerabilities in LXD that could allow a low-privileged user, or a malicious migration source, to write to or delete files on the host as root. CVE-2026-87799 and CVE-2026-85526 have CVSS scores of 9.9, while CVE-2026-85185 is rated 9.6. The issues affect shared and multi-tenant LXD environments, where project-level access could potentially be escalated to control of the underlying host. The article says there is no confirmed exploitation in the wild, although a public proof of concept has been confirmed.

CVE-2026-87799 involves symlinks planted in migration streams processed by rsync or btrfs receive, allowing later entries to be redirected outside the intended volume; optimised ZFS transfers are not affected. CVE-2026-85185 and CVE-2026-85526 involve attacker-controlled btrfs paths in migration headers and optimised backup tarballs, respectively, allowing path traversal during root-level file operations. The latter two flaws affect LXD 4.0.2 and later, while CVE-2026-87799 affects LXD 4.0 and later.

Administrators should upgrade to LXD 4.0.14, 5.0.10, 5.21.8 or 6.10, or use the specified 6.9 build at commit `bf243da`. Until patching, Canonical recommends restricting instance and volume creation, accepting migrations only from trusted servers, avoiding untrusted btrfs backup imports and considering blocking backup imports for non-administrators.