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CVE-2025-43979: Arbitrary OS Command Execution Vulnerability in FIRSTNUM JC21A-04 Devices

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Overview

This report covers the analysis of a critical vulnerability identified in FIRSTNUM JC21A-04 devices. The discovered issue, designated as CVE-2025-43979, enables authenticated attackers to execute arbitrary operating system commands with root privileges. Given the severity of the vulnerability, it’s imperative for all users of these devices to take immediate measures to mitigate its potential impact.

Vulnerability Summary

CVE ID: CVE-2025-43979
Severity: High (CVSS: 7.4)
Attack Vector: Network
Privileges Required: Low (Authentication required)
User Interaction: None
Impact: System compromise or data leakage

Affected Products

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Product | Affected Versions

FIRSTNUM JC21A-04 | Up to and including 2.01ME/FN

How the Exploit Works

The exploit takes advantage of a vulnerability in the xml_action.cgi?method= endpoint of FIRSTNUM JC21A-04 devices. By sending a crafted payload to this endpoint, an authenticated attacker is capable of executing arbitrary operating system commands with root privileges, allowing them to gain complete control over the affected system or access sensitive data.

Conceptual Example Code

Below is a conceptual example of a malicious HTTP request exploiting this vulnerability:

POST /xml_action.cgi?method= HTTP/1.1
Host: target_device_ip
Content-Type: application/json
Authorization: Basic base64_auth_string
{
"command": "malicious_os_command"
}

In this example, `base64_auth_string` is the base64 encoded string of the attacker’s username and password, and `malicious_os_command` is the OS command that the attacker wants to execute with root privileges.

Mitigation

Users are advised to apply the latest vendor patch to remediate this vulnerability. If a patch is not immediately available, users can employ a Web Application Firewall (WAF) or Intrusion Detection System (IDS) as a temporary mitigation measure. This vulnerability underlines the importance of continually monitoring for and applying security updates to all systems and devices.

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Disclaimer:

The information and code presented in this article are provided for educational and defensive cybersecurity purposes only. Any conceptual or pseudocode examples are simplified representations intended to raise awareness and promote secure development and system configuration practices.

Do not use this information to attempt unauthorized access or exploit vulnerabilities on systems that you do not own or have explicit permission to test.

Ameeba and its authors do not endorse or condone malicious behavior and are not responsible for misuse of the content. Always follow ethical hacking guidelines, responsible disclosure practices, and local laws.

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