Advisory Details

May 12th, 2026

Microsoft Windows Message Queueing Double Free Local Privilege Escalation Vulnerability

ZDI-26-309
ZDI-CAN-28559

CVE ID CVE-2026-33838
CVSS SCORE 7.8, AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
AFFECTED VENDORS Microsoft
AFFECTED PRODUCTS Windows
VULNERABILITY DETAILS

This vulnerability allows local attackers to escalate privileges on affected installations of Microsoft Windows that run Message Queueing. An attacker must first obtain the ability to execute low-privileged code on the target system in order to exploit this vulnerability.

The specific flaw exists within the mqac.sys driver. The issue results from the lack of validating the existence of an object prior to performing further free operations on the object. An attacker may be able to leverage this vulnerability to escalate privileges and execute arbitrary code in the context of the kernel.

ADDITIONAL DETAILS Microsoft has issued an update to correct this vulnerability. More details can be found at:
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-33838
DISCLOSURE TIMELINE
  • 2026-01-08 - Vulnerability reported to vendor
  • 2026-05-12 - Coordinated public release of advisory
  • 2026-05-12 - Advisory Updated
CREDIT Anonymous
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