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CVE-2025-20133: Remote Access SSL VPN Vulnerability in Cisco Secure Firewall ASA Software and Secure FTD Software

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Overview

A critical vulnerability, designated as CVE-2025-20133, has been identified within the Remote Access SSL VPN feature of Cisco Secure Firewall ASA Software and Secure FTD Software. This vulnerability could potentially allow an unauthenticated, remote attacker to render the device unresponsive, thereby triggering a Denial of Service (DoS) condition.
This vulnerability is of high importance, particularly for businesses and corporations using Cisco Secure Firewall ASA Software and Secure FTD Software. The successful exploitation of this vulnerability could ultimately lead to system compromise or data leakage, posing significant risks to data integrity and business continuity.

Vulnerability Summary

CVE ID: CVE-2025-20133
Severity: High (8.6 on the CVSS scale)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: Successful exploitation could lead to system disruption (DoS condition) and potential system compromise or data leakage.

Affected Products

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Product | Affected Versions

Cisco Secure Firewall ASA Software | All versions preceding the vendor patch
Cisco Secure FTD Software | All versions preceding the vendor patch

How the Exploit Works

The vulnerability stems from ineffective validation of user-supplied input during the Remote Access SSL VPN authentication process. An attacker can exploit this vulnerability by sending a specially crafted request to the VPN service on an affected device. This malformed request, when processed, causes the device to stop responding to Remote Access SSL VPN authentication requests, ultimately leading to a DoS condition.

Conceptual Example Code

Below is a conceptual HTTP request example that could potentially exploit the vulnerability:

POST /vpn_authenticate HTTP/1.1
Host: target_device_IP
Content-Type: application/json
{ "username": "valid_user", "password": "malicious_payload" }

In this example, the “malicious_payload” is designed to exploit the vulnerability by triggering the DoS condition. The actual form and specifics of the “malicious_payload” would depend on the internal workings of the SSL VPN feature, which are not publicly disclosed for security reasons.

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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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