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.