PyLoad Path Traversal Vulnerability in set_package_data

PyLoad, a free and open-source download manager, is vulnerable to a path traversal vulnerability within its set_package_data API function. Specifically, versions up to and including 0.5.0b3.dev99 fail to properly sanitize the package folder name. This lack of sanitization allows a user with Perms.MODIFY to specify arbitrary directories as download locations for a package. An attacker can leverage this flaw to write files outside the intended download directory, potentially leading to arbitrary code execution if the PyLoad process has sufficient privileges. The vulnerability was disclosed in GHSA-838g-gr43-qqg9 on May 5, 2026.

Attack Chain

1. The attacker gains access to the PyLoad API, potentially through leaked credentials or other vulnerabilities.
2. The attacker crafts a POST request to the /api/add_package endpoint to create a new package with a specified name and download link (e.g., http://example.com/file.txt). The response includes the assigned package ID.
3. The attacker crafts a POST request to the /api/set_package_data endpoint, targeting the newly created package ID.
4. Within the JSON payload for set_package_data, the attacker includes a data object with the key _folder set to an absolute path containing directory traversal sequences (e.g., /users/root/).
5. The PyLoad application, lacking proper sanitization, accepts the attacker-controlled path as the download location.
6. The attacker triggers a download associated with the package.
7. PyLoad attempts to write downloaded files to the attacker-specified path (e.g., /users/root/), potentially overwriting existing files or creating new ones.
8. The attacker achieves arbitrary file write, leading to potential privilege escalation or code execution if writable locations like system configuration files are targeted.

Impact

Successful exploitation allows an attacker to write files to arbitrary locations on the file system with the privileges of the PyLoad process. This could lead to privilege escalation, arbitrary code execution, or denial of service. Given that PyLoad is often deployed on personal servers or NAS devices, the impact could range from data theft to complete system compromise. Affected versions include all PyLoad versions up to and including 0.5.0b3.dev99.

Recommendation

• Upgrade PyLoad to a version beyond 0.5.0b3.dev99 that includes the patch for CVE-2026-42315.
• Deploy the Sigma rule Detect PyLoad set_package_data Path Traversal to detect attempts to exploit this vulnerability by monitoring for suspicious folder paths in set_package_data requests.
• Monitor web server logs for POST requests to /api/set_package_data with suspicious _folder values containing absolute paths and directory traversal sequences.
• Review and restrict API access to PyLoad to only trusted sources to mitigate the risk of unauthorized exploitation.