In January 2022, Microsoft disclosed a new vulnerability tracked as CVE-2022-21843, which affects the Windows IKE Extension. This issue leads to a Denial of Service (DoS) attack, allowing a remote attacker to make the system unresponsive. In this post, we’ll break down the details of this vulnerability, how it differs from similar CVEs, and explore how attackers might exploit it. We’ll also show some demonstration code and discuss mitigation steps.

What is Windows IKE Extension?

Internet Key Exchange (IKE) is a fundamental part of the IPsec protocol suite used in VPNs and secure communications. On Windows, the IKEEXT service handles the negotiation of IPsec security associations and key management.

Severity: Important (Score: 7.5 base CVSS)

- Patch Available: Yes (see Microsoft Security Update Guide)

Unique From: CVE-2022-21848, CVE-2022-21883, CVE-2022-21889, CVE-2022-21890

> This vulnerability allows a remote, unauthenticated attacker to crash the IKEEXT service and potentially disrupt VPN and network security services.

How Does CVE-2022-21843 Work?

The vulnerability exists because the IKEEXT service improperly handles certain specially crafted IKEv2 packets. If an attacker sends these packets to a vulnerable Windows machine (especially where VPN servers are exposed), the service can crash due to unhandled exceptions or memory corruption—resulting in network disruption.

Below is a simplified workflow

1. Find a Target: Locate a public IP exposing the VPN/IKEEXT service (default: UDP port 500 and 450).

Send Malicious Packet: Send a malformed IKEv2 packet that triggers the vulnerability.

3. Service Crash: Target's IKEEXT service crashes, breaking VPN connections and possibly network communication.

This is what’s called a “one-packet DoS”.

Proof-of-Concept Code (Python Pseudocode)

Warning: For educational/research purposes only. Do not run against systems you don’t own.

import socket

TARGET_IP = "192..2.10"    # Replace with target
IKE_PORT = 500

# Craft an IKEv2 malformed packet (pseudocode bytes, not actual malicious buffer)
IKEV2_PAYLOAD = b"\x00\x00\x00\x00" + b"SomeMalformedStuff"

def send_ike_packet(ip, port):
    sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    sock.sendto(IKEV2_PAYLOAD, (ip, port))
    print(f"Sent malformed IKEv2 packet to {ip}:{port}")

send_ike_packet(TARGET_IP, IKE_PORT)


This snippet just sends a minimal UDP packet, but the real exploit would craft specific bytes that trigger the failure in the IKEEXT input handler.

References and Original Sources

- Microsoft Security Response Center: CVE-2022-21843
- Microsoft Patch Tuesday: January 2022
- NVD CVE-2022-21843 Details
- Community discussion: PacketStorm Security

How Is It Different From Other IKEEXT CVEs?

> Some related vulnerabilities published in the same patch batch include CVE-2022-21848, CVE-2022-21883, CVE-2022-21889, and CVE-2022-21890. Each has its *own* specific bug and attack method.

Apply Microsoft patches: Regular security updates (January 2022 and later).

2. Limit IKE exposure: Block UDP 500/450 from untrusted networks (via firewall).

Conclusion

CVE-2022-21843 is a critical example of how a single packet can crash security-critical Windows services. While the DoS impact is serious, timely patching and smart network design can defeat most mass exploitation.

Stay patched, stay safe!

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*This write-up is for educational and defensive purposes only. Always follow your local laws and respect network boundaries.*

Timeline

Published on: 01/11/2022 21:15:00 UTC
Last modified on: 05/23/2022 17:29:00 UTC