CVE-2026-40251 Incus out-of-bounds panic in snapshot metadata handling allows denial of service

What is CVE-2026-40251?

CVE-2026-40251 is a high-severity denial of service vulnerability in lxc incus, published on 6 May 2026. Any signed-in user can exploit it over the network, with no action from the victim.

Official description

Incus is a system container and virtual machine manager. In versions before 7.0.0, missing validation logic in the storage volume import logic allows an authenticated user with access to the storage volume feature to cause the Incus daemon to crash. The backup restore subsystem contains an out-of-bounds panic vulnerability caused by an invalid bounds check when indexing snapshot metadata arrays, and the same flawed pattern also appears in the migration path. When iterating through physical snapshots provided in a backup archive, the loop uses the index to look up corresponding metadata in the parsed `Config.Snapshots` and `Config.VolumeSnapshots` slices. The guard condition `len(slice) >= i-1` is incorrect because it can still evaluate to true when the subsequent slice[i] access is out of bounds.

An attacker can submit a backup archive that contains physical snapshot directories while supplying a tampered `index.yaml` with an empty or truncated snapshot metadata array, causing the daemon to index beyond the end of the metadata slice and crash. Repeated use of this issue can be used to keep Incus offline, causing a denial of service. This issue is fixed in version 7.0.0.

Weakness: CWE-129

Which versions are affected by CVE-2026-40251?

5 open source packages ship an affected version, including github.com/lxc/incus/v6/cmd/incusd, github.com/lxc/incus and github.com/lxc/incus/v6. It affects 1 product.

Products include Linuxcontainers Incus.

How do I fix CVE-2026-40251?

Upgrade github.com/lxc/incus/v6/cmd/incusd to 7.0.0 or later.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-40251 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40251 exists.

Other vulnerabilities in lxc incus

• CVE-2026-33897 Incus vulnerable to arbitrary file read and write through pongo templates Critical 10.0
• CVE-2026-33945 Abitrary file write through systemd-creds option Critical 10.0
• CVE-2026-33898 Local Incus UI web server vulnerable to nuthentication bypass High 8.8
• CVE-2026-23953 Incus container environment configuration newline injection High 8.7
• CVE-2026-23954 Incus container image templating arbitrary host file read and write High 8.7

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as DEBIAN-CVE-2026-40251, GHSA-4m88-wxj4-9qj6, GO-2026-5127, UBUNTU-CVE-2026-40251.