CVE-2026-48484: pyLoad: Lack of Input Size Validation Leads to Denial of Service (DoS) and Process Termination
Description: The API rpc function in apiblueprint.py handles multipart/form-data uploads by reading the whole content of the uploaded file into memory with file.read(). This occurs before the data is sent to the underlying function. Since there is no size limit set at this point, a large file upload can exhaust the server's available memory which led to process termination.
VulnerableCode & Path: https://github.com/pyload/pyload/blob/8e447958b8a66c5899775e725a8b90bce6643004/src/pyload/webui/app/blueprints/apiblueprint.py#L73
Steps to Reproduce: 1. Log in to pyLoad (or use an API key, here i used api to communicate). 2. Prepare a large file (e.g., 10GB) . bash truncate -s 10G largefile.bin 3. Send a multipart request to an API function that accepts a file, such as checkonlinestatuscontainer: bash curl -X POST "http://localhost:8000/api/rpc" \ -H "X-API-Key: YOURAPIKEY" \ -F "func=checkonlinestatuscontainer" \ -F "container=@largefile.bin" 4. Monitor the server's memory usage. The process will attempt to allocate memory for the entire file and last the process will be killed by the kernel. <img width="1902" height="610" alt="dos-process-kill-poc" src="https://github.com/user-attachments/assets/2b9bfd0f-5b9f-48dd-983f-f97dfcc358cc" />
Impact - Denial of Service (DoS): The pyLoad process will be killed by the Operating System's Out-Of-Memory (OOM) killer, or the entire system may become unresponsive due to swap thrashing or memory exhaustion. - Service Instability: Any active downloads or tasks will be interrupted.
Mitigations - Implement File Size Limits: Enforce a maximum size for uploaded files in the web server configuration (e.g., Nginx clientmaxbodysize).
Other sources
pyLoad is a free and open-source download manager written in Python. Prior to 0.5.0b3.dev101, the API rpc function in apiblueprint.py handles multipart/form-data uploads by reading the whole content of the uploaded file into memory with file.read(). This occurs before the data is sent to the underlying function. Since there is no size limit set at this point, a large file upload can exhaust the server's available memory which led to process termination. Version 0.5.0b3.dev101 contains a patch.
— MITRE
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
pip/pyload-ngto a version that resolves this vulnerability.Fixed in 0.5.0b3.dev101 - Upgrade
Upgrade
pyLoadto a version that resolves this vulnerability.Fixed in 0.5.0b3.dev101 - Configuration
Set client_max_body_size to enforce a maximum size for uploaded files.
Nginx client_max_body_size
Event History
Frequently Asked Questions
Who can trigger the denial of service?
An attacker needs to be authenticated to pyLoad, either by logging in or by using an API key. They can send a multipart request to an API function that accepts a file.
What happens when the issue is exploited?
pyLoad reads the entire uploaded file into memory before passing it to the underlying function. A sufficiently large upload can exhaust available memory and cause the process to be terminated by the kernel.
Which API usage is implicated?
The affected path is the rpc API handler for multipart/form-data uploads. The provided example targets the check_online_status_container function with a container file upload.