LXD/MicroCloud mTLS flaw lets attackers impersonate trusted clients without private key (CVE-2026-112816)
Severity: critical · Patch status: patched · Since 2026-10-28 · CVE-2026-112816
Canonical's LXD and MicroCloud, and the Incus fork, check the client certificate chain in mutual-TLS API authentication against the trust store but never verify that the client holds the key for the leaf certificate, so only the leaf proves key possession. An attacker who can reach the HTTPS API can append the public certificate of a trusted client, or of a cluster member, behind their own certificate and be accepted as that identity without its private key. That yields cluster and VM access and, if the impersonated client is privileged, root on the host. Canonical says the bug was referred by the Incus project and confirmed in LXD, and that a MicroCloud member can be impersonated once an attacker intercepts the certificate of a joining member. The LXD HTTPS listener is off by default, so exposure is limited to deployments that enable it and to clusters. No exploitation is reported. Fixed snaps were released on 2026-10-29 for every affected branch (LXD 6.10.1, 5.21.9, 5.0.11, 4.0.15; MicroCloud 3.4.1, 2.1.5), and Incus fixed it in 7.6.0 on 2026-10-30. There is no configuration workaround, so until patching, restrict network access to the HTTPS listener.
What to do
- Immediately update LXD and MicroCloud snaps: sudo snap refresh lxd && sudo snap refresh microcloud, then verify the installed version matches the fixed release (rollout was still in progress)
- Upgrade Incus to 7.6.0 if running Incus
- Until patched, restrict network access to the LXD/MicroCloud HTTPS API (firewall/allowlists); there is no configuration workaround
- Check whether any untrusted party had network reach to the API and audit cluster activity for signs of impersonation
- Avoid exposing core.https_address on untrusted networks
Fixed versions
- LXD 6.10.1 (6/stable), 5.21.9 (5.21/stable), 5.0.11 (5.0/stable), 4.0.15 (4.0/stable)
- MicroCloud 3.4.1 (3/stable), 2.1.5 (2/stable)
- Incus 7.6.0
Sources
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