GHSA-4xg6-52mh-fpw8: Incus: Nil-pointer dereference in createDependentVolumesFromBackup on disk.{Volume,VolumeSnapshots,Pool}
Summary`(*backend).createDependentVolumesFromBackup` in [`internal/server/storage/backend.go`](https://github.com/lxc/incus/blob/d768f81c0a1d985f35ae56219519822b080bf5e3/internal/server/storage/backend.go) contains a cluster of unguarded pointer derefs on every dependent-volume entry's `VolumeSnapshots[i]`, `Volume`, and `Pool` sub-fields. An authenticated user with `can_create_instances` permission on any project can crash the `incusd` daemon by uploading an instance backup tarball whose `dependent_volumes[*]` block contains a nil snapshot pointer (or omits `volume:` / `pool:`).This is a sibling-field variant of the 2026-05-04 batch fix `d768f81c0a1d985f35ae56219519822b080bf5e3` ("Properly check dependent volumes on import"). That commit added `if disk == nil` at the top of the outer loop, but did not guard the four sub-pointer fields the loop body dereferences naked.Vulnerable code[`internal/server/storage/backend.go:9352-9412`](https://github.com/lxc/incus/blob/d768f81c0a1d985f35ae56219519822b080bf5e3/internal/server/storage/backend.go#L9352-L9412):`disk` has type `*config.Config` (declared in [`internal/server/backup/config/backup_config.go:8`](https://github.com/lxc/incus/blob/d768f81c0a1d985f35ae56219519822b080bf5e3/internal/server/backup/config/backup_config.go#L8)). Its `Volume` field is `*api.StorageVolume`, `Pool` is `*api.StoragePool`, `VolumeSnapshots` is `[]*api.StorageVolumeSnapshot` — all yaml `omitempty`. YAML omission decodes to nil for each.The parent fix mental-modeled "outer-iteration variable nil"; it did not walk every sub-field deref inside the loop body. Direct asymmetric-guard variant.ReachAttacker is an authenticated client with `can_create_instances` on any project. Same auth gate as GHSA-8g7m-96c8-8wwc / CVE-2026-47753.`POST /1.0/instances` with `Content-Type: application/octet-stream` and `X-Incus-name: <name>`.Body is a tar containing [`backup/index.yaml`](https://github.com/lxc/incus/blob/d768f81c0a1d985f35ae56219519822b080bf5e3/backup/index.yaml) whose `config:` block has a non-nil `container:` (passes `instances_post.go:854 if bInfo.Config == nil || bInfo.Config.Container == nil`) and a `dependent_volumes:` list with a malformed entry.Chain: `instancesPost` -> `createFromBackup:854` (Container guard passes) -> `pool.CreateInstanceFromBackup` -> `backend.go:782 b.createDependentVolumesFromBackup` -> `backend.go:9374 snap.Name` panics on the nil `*api.StorageVolumeSnapshot` element.`incusd` dies. Persistent DoS on repeat.Minimal [`backup/index.yaml`](https://github.com/lxc/incus/blob/d768f81c0a1d985f35ae56219519822b080bf5e3/backup/index.yaml) (used in the bundled PoC):(The container block must declare at least one device with `type: disk`, `dependent: "true"`, `pool != ""`, `path != "/"` to populate `devicesMap` and reach the second loop. Trivially satisfiable.)An equivalent triggering YAML omits `volume:` or `pool:` from the dependent_volumes entry; in that case `disk.Volume.Project` at 9378 panics instead.Proof of concept (end-to-end against running daemon)Bundled in the report: `make_backup.sh` + 666-byte `poc-inst.tar.gz`.Tested against `incus 7.0.0` (zabbly latest GA, build `1:0~ubuntu24.04~202605201355`) inside a privileged Ubuntu 24.04 container with default `dir` pool.Daemon panic:Stack frame [`backend.go:9374`](https://github.com/lxc/incus/blob/d768f81c0a1d985f35ae56219519822b080bf5e3/backend.go#L9374) is the literal `snap.Name` line.Impact**Severity:** denial of service against the entire `incusd` process. Every container / VM / storage operation on the host (and on the cluster member, if clustered) is aborted; subsequent requests fail until an operator restarts the process.**Privileges required:** any authenticated user with `can_create_instances` on any project. Not behind the admin tier.**Network attack surface:** the Incus REST API on `:8443` or the unix socket.**CWE-476** — Nil-Pointer Dereference. **CVSS estimate:** 6.5 (AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H).**Versions:** v7.0.0 confirmed. The `dependent_volumes` feature did not exist in v6.x, so the vulnerable code is v7-only.Suggested fixReporter notesReported via Privately-Reported Vulnerability against `lxc/incus` by tonghuaroot.
CVSS v4.0: 2.1