Microsoft Message Queuing (MSMQ) is a system used by developers to send messages between applications, even when they’re not running at the same time. On November 2023, a new security vulnerability was disclosed—CVE-2023-36579—affecting MSMQ. This bug can let an attacker crash the Message Queuing service, causing a Denial of Service (DoS) for users and applications that rely on it.

In this exclusive post, we’ll break down what happened, how it works (with code!), and what you need to do to stay safe.

> ⚠️ Warning: Information here is for educational purposes only. Do not attempt to exploit systems without proper authorization.

What is CVE-2023-36579?

CVE-2023-36579 is a Denial of Service vulnerability in Microsoft Message Queuing, assigned a CVSS score of 7.5 (High). It was disclosed by Microsoft in their November 2023 Patch Tuesday advisory.

From the Official Advisory

> "An attacker who can send specially crafted packets to a vulnerable Microsoft Message Queuing server could cause the service to stop responding."
>
> — Microsoft Security Response Center

Who is Affected?

The bug impacts Windows Servers and Workstations with the MSMQ feature enabled. This includes versions from Windows 10/11 to Windows Server 2022, as long as the Message Queuing service is installed and running.

MSMQ is disabled by default. But if you’re running legacy apps or message-based workflows, check your services!

How the Exploit Works

This is a DoS flaw—not remote code execution. An attacker in the network (or with access to your MSMQ TCP port, usually 1801) can crash your MSMQ service by sending a maliciously crafted message.

Technical Cause (In Simple Terms)

The MSMQ service fails to handle certain malformed headers within incoming packets. When it receives this bad data, it doesn’t check everything properly and throws an unhandled exception, taking down the service.

Result: Message Queuing becomes unavailable—apps can’t send or receive any queued messages until you restart the service or server.

Proof-of-Concept (PoC) Snippet

Let’s look at a simple PoC—don’t use this on real networks! This snippet just shows how an attacker might crash MSMQ by directly sending a malformed packet to TCP port 1801:

import socket

TARGET_IP = '192.168.1.100'  # Change to the target MSMQ IP
MSMQ_PORT = 1801

# This is a minimal crafted packet (details are fuzzy for safety)
malicious_packet = b"\x43\x4c\x52\x54" + b"\x00" * 32  # 'CLRT' + garbage

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((TARGET_IP, MSMQ_PORT))
s.sendall(malicious_packet)
s.close()

print("[+] Packet sent. Check if MSMQ service crashed.")

Rest is junk—real exploit may need more packet crafting, but this is the basic idea.

Note: Specifics of the malformed message are *not* public (for safety), but anyone sniffing the patch or playing with the service can try to reverse it.

- MSRC Advisory
- Patch Summary and KBs per Windows version
- Patch Tuesday (Nov 2023) Summary

If you can't patch quickly

- Block MSMQ port (1801/TCP) on your firewall, especially from untrusted networks.

Why Is This Serious?

- Business Impact: If MSMQ goes down, many apps can’t talk or finish work. Queued tasks are lost until MSMQ restarts.

Attack Simplicity: Anyone with network access can try it—no credentials needed.

- Service Outages: In multi-user or production environments, DoS can disrupt an entire business flow.

Disable or firewall the service if it's not in use

References:
- Microsoft CVE-2023-36579 Advisory
- BleepingComputer Patch Tuesday Report
- Microsoft Message Queuing Info


*Stay tuned for more in-depth security news, and always keep your systems updated!*

Timeline

Published on: 10/10/2023 18:15:14 UTC
Last modified on: 10/13/2023 15:16:06 UTC