Affected: pyload

pyLoad is a free and open-source download manager written in Python. In versions prior to 0.5.0b3.dev91, pyLoad web interface contained insufficient input validation in both the Captcha script endpoint and the Click'N'Load (CNL) Blueprint. This flaw allowed untrusted user input to be processed unsafely, which could be exploited by an attacker to inject arbitrary content into the web UI or manipulate request handling. The vulnerability could lead to client-side code execution (XSS) or other unintended behaviors when a malicious payload is submitted. user-supplied parameters from HTTP requests were not adequately validated or sanitized before being passed into the application logic and response generation. This allowed crafted input to alter the expected execution flow. CNL (Click'N'Load) blueprint exposed unsafe handling of untrusted parameters in HTTP requests. The application did not consistently enforce input validation or encoding, making it possible for an attacker to craft malicious requests. Version 0.5.0b3.dev91 contains a patch for the issue.

Affected: PyPI: pyload-ng

### Summary pyLoad web interface contained insufficient input validation in both the Captcha script endpoint and the Click'N'Load (CNL) Blueprint. This flaw allowed untrusted user input to be processed unsafely, which could be exploited by an attacker to inject arbitrary content into the web UI or manipulate request handling. The vulnerability could lead to client-side code execution (XSS) or other unintended behaviors when a malicious payload is submitted.

user-supplied parameters from HTTP requests were not adequately validated or sanitized before being passed into the application logic and response generation. This allowed crafted input to alter the expected execution flow. CNL (Click'N'Load) blueprint exposed unsafe handling of untrusted parameters in HTTP requests. The application did not consistently enforce input validation or encoding, making it possible for an attacker to craft malicious requests.

### PoC

1. Run a vulnerable version of pyLoad prior to commit [`f9d27f2`](https://github.com/pyload/pyload/pull/4624). 2. Start the web UI and access the Captcha or CNL endpoints. 3. Submit a crafted request containing malicious JavaScript payloads in unvalidated parameters (`/flash/addcrypted2?jk=function(){alert(1)}&crypted=12345`). 4. Observe that the payload is reflected and executed in the client’s browser, demonstrating cross-site scripting (XSS).

Example request:

```http GET /flash/addcrypted2?jk=function(){alert(1)}&crypted=12345 HTTP/1.1 Host: 127.0.0.1:8000…