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Critical unauthorised RCE vulnerability in MSMQ service

Check Point Research recently discovered three vulnerabilities in the "Microsoft Message Queuing" service, commonly known as MSMQ.

These vulnerabilities were disclosed to Microsoft and patched in the April Patch Tuesday update. The most severe of these, dubbed QueueJumper by CPR (CVE-2023-21554), is a critical vulnerability that could allow unauthorised attackers to remotely execute arbitrary code in the context of the Windows service process mqsvc.exe.

Three vulnerabilities in the MSMQ service were discovered, with all of them  patched in the April Patch Tuesday update:

CVE-2023-21554 (QueueJumper) — Unauthorised Remote Code Execution
CVE-2023-21769 — Unauthorised Remote Application Level DoS (service crash)
CVE-2023-28302 — Unauthorised Remote Kernel Level DoS (Windows BSOD)

The most significant vulnerability allows unauthorised attackers to execute arbitrary code in the context of the Windows service process, mqsvc.exe.

MSMQ is provided as an optional Windows component and is still available on all Windows operating systems, including the latest Windows Server 2022 and Windows 11

According to Microsoft, Microsoft Message Queuing is a message infrastructure and a development platform for creating distributed, loosely-coupled messaging applications for the Microsoft Windows operating system. Message Queuing applications can use the Message Queuing infrastructure to communicate across heterogeneous networks and with computers that may be offline. Message Queuing provides guaranteed message delivery, efficient routing, security, transaction support, and priority-based messaging.

The most recent Microsoft documents discussing the service were updated in 2016. Some MSMQ experts published a blog post in January 2020 exploring the retiring trend of the service. Despite being considered a "forgotten" or "legacy" service, MSMQ is still available on all Windows operating systems, including the latest Windows Server 2022 and Windows 11 and is provided as an optional Windows component. Users can easily enable the service via the Control Panel or via PowerShell command “Install-WindowsFeature MSMQ-Services”.

The QueueJumper Vulnerability
The CVE-2023-21554  vulnerability allows an attacker to potentially execute code remotely and without authorisation by reaching the TCP port 1801. In other words, an attacker could gain control of the process through just one packet to the 1801/tcp port with the exploit, triggering the vulnerability.

The Impact
The attack vector sends packets to the service port 1801/tcp. In order to have a better understanding of the potential impact in the real world of this service, CPR did a full Internet scan. It found that more than ~360,000 IPs have the 1801/tcp open to the internet and are running the MSMQ service.

Note that this only includes the number of hosts facing the Internet and does not account for computers hosting the MSMQ service on internal networks, where the number should be far more.

The MSMQ service is a "middleware" service that some popular software relies on. When the user installs the popular software, the MSMQ service is enabled on Windows, which may be done without the user’s knowledge.

Protection & Mitigation
CPR recommends all Windows admins check their servers and clients to see if the MSMQ service is installed. Users can check if there is a service running named ‘Message Queuing’, and TCP port 1801 is listening on the computer. If it is installed, double-check if it is needed. Closing unnecessary attack surfaces is a good security practice.

"For this particular vulnerability we discussed, we recommend users install Microsoft's official patch as soon as possible," CPR says.

"If your business requires MSMQ but is unable to apply Microsoft's patch right now, you may block the inbound connections for 1801/tcp from untrusted sources with Firewall rules (for example, blocking Internet connections to 1801/tcp for Internet-facing machines), as a workaround. 

"Check Point IPS has developed and deployed a signature named “Microsoft Message Queuing Remote Code Execution (CVE-2023-21554)” to detect and protect our customers against the QueueJumper vulnerability."

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