Windows Message Queuing: Out-of-bounds read causes information disclosure

Summary

The Queue Manager of Windows Message Queuing (MSMQ) contains an out-of-bounds read (CWE-125). A remote, unauthenticated attacker can send crafted traffic to the MSMQ service over the network and read parts of memory, which can expose sensitive data. Integrity and availability are not affected, and no user interaction is required. Exposure is mainly a concern for systems where MSMQ is enabled and reachable from untrusted networks.

Affected

• Windows 10 Version 1607 (builds before 10.0.14393.9612)
• Windows 10 Version 1809 (builds before 10.0.17763.9376)
• Windows 10 Version 21H2 (builds before 10.0.19044.7807)
• Windows 10 Version 22H2 (builds before 10.0.19045.7807)
• Windows 11 Version 23H2 (builds before 10.0.22631.7652)
• Windows 11 Version 24H2 (builds before 10.0.26100.9711)
• Windows 11 Version 25H2 (builds before 10.0.26200.9711)
• Windows 11 Version 26H1 (builds before 10.0.28000.3231)
• Windows 11 Version 26H2 (builds before 10.0.26300.9711)
• Windows Server 2012 and Server Core (builds before 6.2.9200.26434)
• Windows Server 2012 R2 and Server Core (builds before 6.3.9600.23470)
• Windows Server 2016 (builds before 10.0.14393.9612)

Fixed in

• Windows 10 Version 1607: build 10.0.14393.9612 via KB5126868 (October 2026 cumulative update)
• Latest Windows 10 Version 1607 build: 10.0.14393.9615 via KB5134123 (non-security out-of-band update)
• Other products: fixed builds as listed in the Microsoft Security Update Guide
• Windows 10 Version 1607 is at end of support as of October 13, 2026; no extended security update option has been confirmed.

Workaround

• No workaround is required where the security update is installed.
• Identify hosts with the Message Queuing Windows feature or a running MSMQ service.
• Disable the Message Queuing Windows feature on systems that do not need it.
• Restrict access to MSMQ with firewall rules on systems that must keep the feature. The default ports were not verified.

Exploitation

• Exploited in the wild: Unknown. CISA SSVC lists exploitation as none, with automatable set to yes.
• Not listed in CISA KEV.
• No public proof-of-concept exploit found in the sources checked.
• EPSS score: 0.01005.

Our recommendation

• Inventory all Windows 10 Version 1607 and Windows Server 2016 hosts and check whether MSMQ is installed.
• Install KB5126868 at minimum, preferably the latest build KB5134123.
• Disable MSMQ where it is not required and restrict it to known internal sources where it is.
• Check the other listed Windows versions against the Microsoft Security Update Guide and patch them.
• Plan the migration away from Windows 10 Version 1607, since it no longer receives security updates.

Public exploits iAttack code is publicly available (PoC on GitHub, Metasploit or Exploit-DB).

PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.

Research sources

• Microsoft Security Update Guide: CVE-2026-85334 msrc.microsoft.com
• KB5134123: Windows 10 1607 update (October 2026) support.microsoft.com
• Windows 10 1607 and Windows Server 2016 release health status learn.microsoft.com
• SentinelOne vulnerability database: CVE-2026-85334 www.sentinelone.com
• Vulners MSCVE record: MS:CVE-2026-85334 vulners.com
• OpenCVE: CVE-2026-85334 app.opencve.io
• VulDB: CVE-2026-85334 vuldb.com
• Patch Tuesday October 2026 changelog (KACE) changelog.kace.com

Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 2 Nov 2026, 18:36.