Overview
We are currently investigating a critical vulnerability, CVE-2025-53890, that resides within the CAPTCHA processing code of pyLoad, a popular open-source download manager written in Python. This vulnerability could potentially affect thousands of users who rely on pyLoad for managing their downloads. The severity of this issue is underlined by its CVSS Severity Score of 9.8, which signifies a critical impact. The flaw can allow unauthenticated remote attackers to execute arbitrary code, resulting in severe consequences such as session hijacking, credential theft, and even full system remote code execution.
Vulnerability Summary
CVE ID: CVE-2025-53890
Severity: Critical (9.8/10)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: Session hijacking, Credential theft, Full system remote code execution
Affected Products
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Product | Affected Versions
pyLoad | Prior to 0.5.0b3.dev89
How the Exploit Works
The vulnerability lies in pyLoad’s CAPTCHA processing code. It is an unsafe JavaScript evaluation vulnerability, which means it allows the execution of arbitrary code in the client browser without any form of user interaction or authentication. This code execution can extend to the backend server and can be exploited by remote attackers. The vulnerability can lead to a full system compromise, allowing attackers to hijack sessions, steal credentials, and execute code remotely.
Conceptual Example Code
To illustrate how an attacker might exploit this vulnerability, consider the following hypothetical HTTP request:
POST /pyload/captcha/endpoint HTTP/1.1
Host: target.example.com
Content-Type: application/json
{ "captcha_solution": "eval('malicious_code')" }In this example, the attacker is embedding malicious JavaScript code in the `captcha_solution` field. When this request is processed by the server, it evaluates the malicious JavaScript code leading to the potential compromise of the system.
Mitigation Guidance
Users are strongly urged to update their pyLoad software to version 0.5.0b3.dev89 or later where the patch for this issue has been included. If updating is not an immediate option, using a Web Application Firewall (WAF) or Intrusion Detection System (IDS) can offer temporary mitigation. However, these are temporary measures and updating the software is the most reliable way to ensure protection against this severe vulnerability.