CVE-2026-50447: Windows Message Queuing Buffer Overflow

CVE-2026-50447 Overview

CVE-2026-50447 is a heap-based buffer overflow vulnerability in Windows Message Queuing (MSMQ) that allows an unauthenticated remote attacker to execute arbitrary code over a network. The flaw is tracked under CWE-122: Heap-based Buffer Overflow and carries a CVSS 3.1 base score of 9.8. Exploitation requires no user interaction and no prior privileges, making any internet-exposed MSMQ service a viable target. Microsoft published the advisory in the Microsoft Security Update Guide.

Critical Impact
An unauthenticated attacker can send a crafted MSMQ packet over the network to trigger memory corruption and gain remote code execution on the target host with service-level privileges.

Affected Products

Microsoft Windows (Message Queuing service enabled)
Windows Server deployments with the MSMQ role installed
Refer to the Microsoft Security Update Guide for the authoritative list of affected builds

Discovery Timeline

2026-07-14 - CVE-2026-50447 published to NVD
2026-07-15 - Last updated in NVD database

Technical Details for CVE-2026-50447

Vulnerability Analysis

The vulnerability resides in the Windows Message Queuing service, which processes MSMQ protocol messages received on TCP port 1801 by default. A heap-based buffer overflow occurs when the service parses attacker-controlled fields inside an inbound message. Insufficient bounds checking on the length or structure of specific message components allows a crafted packet to write beyond the allocated heap buffer.

Successful exploitation corrupts adjacent heap metadata or object pointers, giving the attacker control over program flow. Because the MSMQ service typically runs with elevated privileges, code execution occurs in the security context of the service account. The EPSS score of 0.928% reflects current exploitation probability, though prior MSMQ vulnerabilities such as QueueJumper have historically drawn active attacker interest.

Root Cause

The root cause is improper validation of length-tagged fields inside MSMQ protocol messages before they are copied into a fixed-size heap allocation. When the declared field length exceeds the destination buffer, the copy operation overflows the heap chunk. See CWE-122 for background on this class of defect.

Attack Vector

An attacker sends a single crafted MSMQ packet to a vulnerable host reachable over the network. The attack requires no authentication, no user interaction, and low attack complexity. Hosts that expose TCP port 1801 to untrusted networks are directly reachable. No public proof-of-concept is available at the time of publication. Refer to the Microsoft Security Update Guide for technical details.

Detection Methods for CVE-2026-50447

Indicators of Compromise

Unexpected mqsvc.exe process crashes or Windows Error Reporting entries referencing MSMQ modules
Inbound TCP connections to port 1801 from external or unusual source addresses
Child processes spawned by mqsvc.exe, such as cmd.exe, powershell.exe, or rundll32.exe
New service installations or scheduled tasks created shortly after MSMQ network activity

Detection Strategies

Monitor for anomalous process lineage where the Message Queuing service parent spawns interactive shells or scripting engines
Alert on MSMQ service crashes followed by service restarts within short time windows
Inspect network telemetry for oversized or malformed MSMQ packets targeting port 1801

Monitoring Recommendations

Enable Windows Event Log forwarding for the System and Application logs on all hosts with the MSMQ role
Capture network flow data for TCP 1801 and correlate external sources against asset inventories
Baseline legitimate MSMQ traffic patterns and alert on deviations in message size or client geography

How to Mitigate CVE-2026-50447

Immediate Actions Required

Apply the Microsoft security update referenced in the Microsoft Security Update Guide to all Windows hosts running the Message Queuing service
Inventory systems with the MSMQ feature enabled using Get-WindowsFeature MSMQ or equivalent tooling
Block inbound TCP port 1801 at the network perimeter and restrict it to trusted internal segments
Disable the Message Queuing service on hosts that do not require it

Patch Information

Microsoft has published a security update for CVE-2026-50447. Consult the Microsoft Security Update Guide for the specific KB articles, affected builds, and download packages that correspond to each Windows version in the environment.

Workarounds

Disable the Windows Message Queuing service where it is not required for business operations
Restrict TCP port 1801 to allow-listed internal source addresses using Windows Firewall or network ACLs
Segment MSMQ-dependent applications into isolated network zones with strict ingress filtering

bash

# Check for MSMQ presence and disable the service if not required
Get-Service -Name MSMQ
Stop-Service -Name MSMQ -Force
Set-Service -Name MSMQ -StartupType Disabled

# Block inbound TCP 1801 at the host firewall
New-NetFirewallRule -DisplayName "Block MSMQ 1801 Inbound" `
  -Direction Inbound -Protocol TCP -LocalPort 1801 -Action Block