VDB-363195 · CVE-2026-40403 · EUVD-2026-29664

Microsoft Windows up to Server 2025 Graphics heap-based overflow

CVSS Meta Temp Score CVSS is a standardized scoring system to determine possibilities of attacks. The Temp Score considers temporal factors like disclosure, exploit and countermeasures. The unique Meta Score calculates the average score of different sources to provide a normalized scoring system.	Current Exploit Price (≈) Our analysts are monitoring exploit markets and are in contact with vulnerability brokers. The range indicates the observed or calculated exploit price to be seen on exploit markets. A good indicator to understand the monetary effort required for and the popularity of an attack.	CTI Interest Score Our Cyber Threat Intelligence team is monitoring different web sites, mailing lists, exploit markets and social media networks. The CTI Interest Score identifies the interest of attackers and the security community for this specific vulnerability in real-time. A high score indicates an elevated risk to be targeted for this vulnerability.
8.1	$5k-$25k	0.00

Summaryinfo

A vulnerability was found in Microsoft Windows. It has been rated as critical. This affects an unknown function of the component Graphics. Performing a manipulation results in heap-based overflow. This vulnerability is known as CVE-2026-40403. Attacking locally is a requirement. No exploit is available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability classified as critical has been found in Microsoft Windows. This affects an unknown function of the component Graphics. The manipulation with an unknown input leads to a heap-based overflow vulnerability. CWE is classifying the issue as CWE-122. A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc(). This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

Heap-based buffer overflow in Windows Win32K - GRFX allows an authorized attacker to execute code locally.

The weakness was published 05/12/2026 as confirmed security update guide (Website). It is possible to read the advisory at msrc.microsoft.com. This vulnerability is uniquely identified as CVE-2026-40403. The exploitability is told to be easy. Attacking locally is a requirement. The technical details are unknown and an exploit is not publicly available. The pricing for an exploit might be around USD $5k-$25k at the moment (estimation calculated on 06/03/2026).

The vulnerability scanner Nessus provides a plugin with the ID 314355 (KB5087539: Windows Server 2025 Security Update (May 2026)), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 10.0.26200.8390 or 10.0.26200.8457 eliminates this vulnerability. A possible mitigation has been published immediately after the disclosure of the vulnerability.

The vulnerability is also documented in the databases at Tenable (314355) and EUVD (EUVD-2026-29664). Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.

Productinfo

Type

Operating System

Vendor

Microsoft

Name

Windows

Version

License

commercial

Website

Vendor: https://www.microsoft.com/
Product: https://www.microsoft.com/en-us/windows

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 8.8
VulDB Meta Temp Score: 8.1

VulDB Base Score: 8.8
VulDB Temp Score: 7.7
VulDB Vector: 🔒
VulDB Reliability: 🔍

Vendor Base Score (Microsoft): 8.8
Vendor Vector (Microsoft): 🔒

CNA Base Score: 8.8
CNA Vector (Microsoft): 🔒

CVSSv2info

AV	AC	Au	C	I	A
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Vector	Complexity	Authentication	Confidentiality	Integrity	Availability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Heap-based overflow
CWE: CWE-122 / CWE-119
CAPEC: 🔒
ATT&CK: 🔒

Physical: Partially
Local: Yes
Remote: No

Availability: 🔒
Status: Unproven

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

0-Day	Unlock	Unlock	Unlock	Unlock
Today	Unlock	Unlock	Unlock	Unlock

Nessus ID: 314355
Nessus Name: KB5087539: Windows Server 2025 Security Update (May 2026)

Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Upgrade
Status: 🔍

Reaction Time: 🔒
0-Day Time: 🔒
Exposure Time: 🔒

Upgrade: Windows 10.0.26200.8390/10.0.26200.8457

Timelineinfo

05/12/2026 VulDB entry created
05/12/2026 +0 days Advisory disclosed
05/12/2026 +0 days Countermeasure disclosed
06/03/2026 +21 days VulDB entry last update