Critical LXD and MicroCloud flaw lets attackers impersonate trusted clients
Canonical said it has released fixed versions of LXD and MicroCloud for CVE-2026-112816, a critical flaw that can let an attacker log in as a trusted client without holding that client's private key. The vulnerability carries a maximum CVSS score of 10.0, according to the CVE record cited in the report.
The attacker must reach the HTTPS API over the network and obtain the public certificate of a client that the server already trusts, Canonical said. The flaw affects the mutual TLS certificate check: the server verifies ownership of the first certificate in a chain, but accepted a trusted public certificate attached later in a chain chosen by the attacker.
After authentication, the attacker acts as the impersonated client and can access the cluster and its virtual machines, Canonical said. If that client has administrative privileges, the attacker could gain root access to the host machine.
A standalone LXD server does not expose the vulnerable API by default, according to Canonical. It listens on a local socket unless an administrator enables the network API with the core.https_address setting. MicroCloud has an additional exposure path: Canonical said an attacker who captures a member's public certificate while it joins the cluster can use that certificate to log in as the member.
The CVE record lists LXD 4.0.14, 5.0.10, 5.21.8 and 6.9 as affected before their respective fixed releases. Incus, the community fork of LXD, fixed the same flaw in version 7.6.0 after reporting it, according to the report.
There is no public sign that the flaw has been used in an attack. The CISA assessment cited in the report says it is not known to have been exploited, and the vulnerability is not listed in CISA's Known Exploited Vulnerabilities catalog.
Canonical said administrators should update LXD and MicroCloud. For snap installations, its guidance is to run sudo snap refresh lxd and sudo snap refresh microcloud, then verify the installed versions because the fixed LXD point releases were still moving from the candidate channel to stable. The Incus project said it has no configuration fix; restricting network access to the listener is the available interim measure.