Executive brief
LXD is a system container and virtual machine manager used to run isolated environments on Linux. A vulnerability in how LXD imports backup files allows a user with limited permissions to bypass security restrictions and gain full administrative control over the host server. By providing a specially crafted backup file, an attacker can create a container that has unauthorized access to the host's files and resources, potentially leading to a complete system takeover.
Technical details
The vulnerability arises from a discrepancy between two configuration files within a backup tar archive: 'backup/index.yaml' and 'backup/container/backup.yaml'. LXD's 'AllowInstanceCreation' function validates project restrictions (such as blocking privileged containers or host device passthrough) against 'index.yaml'. However, the actual instance is created using the configuration in 'backup.yaml', which is not re-validated against project-specific restrictions. An attacker with instance-creation rights in a restricted project can craft a backup where 'index.yaml' appears benign while 'backup.yaml' contains malicious configurations like 'security.privileged=true' or 'raw.lxc' host mounts. This allows for container escape and full host compromise. Patches are available in LXD series 5.0, 5.21, and 6.
Affected products
- Canonical LXD >= 0.0.0-20210305023314-538ac3df036e, <= 0.0.0-20260226085519-736f34afb267
Timeline
- 2026-04-09: advisory: Initial GitHub Advisory published
- 2026-04-10: disclosed: Full advisory details and CVE-2026-34178 assigned