What is the CVSS score of CVE-2026-40404?

CVE-2026-40404 has a CVSS 3.1 base score of 7.8 (High). CVSS vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. EPSS exploitation probability: 0.1%.

Which versions of Windows UDFS Driver are affected by CVE-2026-40404?

A local privilege escalation vulnerability in Microsoft Windows UDFS driver (CVE-2026-40404, CVSS 7.8) enables standard users to achieve complete system control through manipulated disc media.. A patch is available.

How to fix or mitigate CVE-2026-40404?

Within 24 hours: Audit which Windows endpoints require UDFS functionality and disable the driver on systems where optical disc support is unnecessary; enable logging for UDF media mounting attempts. Within 7 days: Restrict physical media access and UDF image mounting to administrative personnel only; implement application controls blocking unauthorized disc-mounting utilities. Within 30 days: Monitor Microsoft security advisories for CVE-2026-40404 patch availability and prepare phased deployment plan across your Windows fleet; test patch in lab environment before production rollout.

Windows UDFS Driver CVE-2026-40404

EUVD-2026-35656 HIGH

Heap-based Buffer Overflow (CWE-122)

2026-06-09 secure@microsoft.com

GHSA-h2q2-g4v6-v8fh

Buffer Overflow Heap Overflow Microsoft Windows 10 1607 Windows 10 1809 Windows 10 21h2 Windows 10 22h2 Windows 11 23h2 Windows 11 24h2 Windows 11 25h2 Windows 11 26h1 Windows Server 2012 Windows Server 2016 Windows Server 2019 Windows Server 2022 Windows Server 2025

7.8

CVSS 3.1 · Vendor: microsoft

Temporal: 6.8

Severity by source

Vendor (microsoft) PRIMARY

7.8 HIGH

AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CIRCL (temporal)

6.8 MEDIUM

cvss

Primary rating from Vendor (microsoft).

CVSS VectorVendor: microsoft

Attack Vector

Local

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Lifecycle Timeline

Patch available

Jun 09, 2026 - 19:03 EUVD

Analysis Generated

Jun 09, 2026 - 17:34 vuln.today

CVE Published

Jun 09, 2026 - 17:17 nvd

HIGH 7.8

DescriptionCVE.org

Windows Universal Disk Format File System Driver (UDFS) Elevation of Privilege Vulnerability

AnalysisAI

Local privilege escalation in the Microsoft Windows Universal Disk Format File System (UDFS) driver allows an authenticated low-privileged user to gain SYSTEM-level code execution by triggering a heap-based buffer overflow (CWE-122). The flaw affects Windows endpoints where the UDFS kernel driver parses attacker-controlled UDF-formatted media (typically optical discs or mounted disc images). No public exploit identified at time of analysis and the issue is not currently listed on CISA KEV.

Technical ContextAI

UDFS.sys is the Windows kernel-mode driver responsible for mounting and parsing volumes formatted with the Universal Disk Format (UDF, ISO/IEC 13346 / ECMA-167) - the file system used by DVD-Video, Blu-ray, and many ISO images. CWE-122 (Heap-based Buffer Overflow) indicates the driver fails to correctly bound-check fields within UDF on-disk structures (e.g., file identifiers, allocation descriptors, or partition maps) before copying them into kernel heap allocations. Because parsing occurs in ring-0, corrupting non-paged or paged pool memory can be steered toward arbitrary kernel write primitives and SYSTEM-token theft. The Microsoft tag set ('Buffer Overflow, Heap Overflow, Microsoft') and the CVSS scope of S:U with full CIA impact are consistent with an in-process kernel pool corruption rather than a sandbox escape.

RemediationAI

Patch available per vendor advisory - apply the Microsoft security update referenced at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-40404 via Windows Update, WSUS, or your preferred patch management channel as soon as the corresponding KB has been validated in your environment. Exact fix KB numbers and build versions are not enumerated in the provided data and should be taken from the MSRC entry. As compensating controls until patching completes, disable automatic mounting of optical media and ISO images by setting the AutoRun/AutoPlay policies (HKLM\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer\NoDriveTypeAutoRun) and consider blocking interactive ISO/IMG mounting via Group Policy or AppLocker - note this breaks legitimate workflows for users who mount disc images for software installs. On servers without a business need for optical/UDF media, the UDFS driver service can be disabled (sc.exe config udfs start= disabled) but verify no backup, imaging, or media-handling workloads depend on it before doing so.