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CVE-2025-20239: Denial of Service Vulnerability in Cisco IOS, IOS XE, ASA and FTD Software

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Overview

This blog post is set to discuss the recently discovered vulnerability, CVE-2025-20239, which poses a significant threat to the Internet Key Exchange Version 2 (IKEv2) feature of various Cisco software. This vulnerability is particularly alarming due to its potential to allow an unauthenticated, remote attacker to cause a denial of service condition. As Cisco software is widely utilized, this vulnerability has wide-ranging implications and requires immediate attention.

Vulnerability Summary

CVE ID: CVE-2025-20239
Severity: High (8.6)
Attack Vector: Network
Privileges Required: None
User Interaction: None
Impact: Potential system compromise or data leakage

Affected Products

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Product | Affected Versions

Cisco IOS Software | All versions prior to the vendor patch
Cisco IOS XE Software | All versions prior to the vendor patch
Cisco Secure Firewall ASA Software | All versions prior to the vendor patch
Cisco Secure Firewall FTD Software | All versions prior to the vendor patch

How the Exploit Works

The CVE-2025-20239 vulnerability takes advantage of a flaw in the processing of IKEv2 packets within the affected Cisco software. An attacker can craft specific IKEv2 packets and send them to the targeted device. These packets can trigger a memory leak, leading to a denial of service condition. In the case of Cisco IOS and IOS XE Software, this could cause the device to unexpectedly reload, while in the case of Cisco ASA and FTD Software, it could lead to exhaustion of system memory, causing system instability and the inability to establish new IKEv2 VPN sessions.

Conceptual Example Code

While the exact methods will vary based on the attacker’s skill and the specific target, a conceptual example of an attack might look like this:

POST /IKEv2/process HTTP/1.1
Host: target.example.com
Content-Type: application/x.ikev2
{ "IKEv2_packet": "crafted_malicious_packet_data" }

In this example, the attacker sends a crafted IKEv2 packet to the vulnerable endpoint (“IKEv2/process” in this example), which subsequently triggers the memory leak and denial of service condition.

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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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