CVE-2026-85526: Path traversal via Btrfs optimized-backup subvolumes[].path enables root file/dir manipulation in LXD
Path traversal in the Btrfs storage driver (unpackVolume) in Canonical LXD on Linux allows an authenticated user with instance creation privileges to delete or replace arbitrary files and directories on the host filesystem as root via a crafted subvolumes[].path entry in backup/optimizedheader.yaml during a btrfs optimized backup import.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Canonical LXDto a version that resolves this vulnerability.Fixed in 4.0.14
Event History
Frequently Asked Questions
Can an unauthenticated remote attacker exploit this issue?
No. Exploitation requires an authenticated LXD user with privileges to create instances.
What environment and operation are required for exploitation?
The affected workflow is importing a Btrfs optimized backup. The attacker must provide a crafted subvolumes[].path entry in the backup's optimized_header.yaml file.
What is the impact on the host if exploitation succeeds?
The attacker can cause arbitrary host files and directories to be deleted or replaced. These operations occur with root privileges.