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CVE-2025-20244: Denial of Service Vulnerability in Cisco Secure Firewall

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Overview

This report discusses a critical vulnerability, CVE-2025-20244, that poses a significant threat to the Cisco Secure Firewall Adaptive Security Appliance (ASA) Software and Cisco Secure Firewall Threat Defense (FTD) Software. This vulnerability could allow a remote attacker, authenticated as a VPN user, to cause an unexpected system reload and subsequently a denial of service (DoS) condition.

Vulnerability Summary

CVE ID: CVE-2025-20244
Severity: High (7.7 CVSS Score)
Attack Vector: Network
Privileges Required: Low (Authenticated VPN User)
User Interaction: None
Impact: Potential system compromise or data leakage, denial of service condition

Affected Products

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Product | Affected Versions

Cisco Secure Firewall Adaptive Security Appliance (ASA) Software | All versions prior to patch
Cisco Secure Firewall Threat Defense (FTD) Software | All versions prior to patch

How the Exploit Works

The vulnerability CVE-2025-20244 is due to incomplete error checking when parsing an HTTP header field value. An attacker could exploit this vulnerability by sending a crafted HTTP request to a targeted Remote Access SSL VPN service on an affected device. A successful exploit could cause a DoS condition, which would cause the affected device to reload.

Conceptual Example Code

Below is a conceptual example of how the vulnerability might be exploited. This is a crafted HTTP request that could potentially trigger the vulnerability:

POST /targeted/vpn/service HTTP/1.1
Host: target.example.com
Content-Type: application/json
VPN-User: authenticated user
{ "malicious_payload": "crafted HTTP header field value causing error" }

Please note that the above is a simplified representation and actual exploitation may require more sophisticated techniques.

Mitigation

To mitigate this vulnerability, it is recommended to apply the vendor patch as soon as it becomes available. Until then, using a Web Application Firewall (WAF) or Intrusion Detection System (IDS) may serve as temporary mitigation. Regularly updating all software and maintaining vigilance for any unusual network activity can also provide additional layers of security.

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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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