Local code execution via Win32K heap overflow
Published May 12, 2026 · Updated May 12, 2026
Heap-based buffer overflow in Windows Win32K - GRFX allows local users to execute code through a locally initiated attack. The GRFX path performs an out-of-bounds heap write while handling locally supplied data; Microsoft has not disclosed the affected routine or input format. The attacker must already hold low privileges and run code locally, after which code executes outside the original security authority.
Summary
What happened
Heap-based buffer overflow in Windows Win32K - GRFX allows local users to execute code through a locally initiated attack. The GRFX path performs an out-of-bounds heap write while handling locally supplied data; Microsoft has not disclosed the affected routine or input format. The attacker must already hold low privileges and run code locally, after which code executes outside the original security authority.
The record
- CVE
- CVE-2026-40403
- Published
- May 12, 2026
- Updated
- May 12, 2026
- Vendor
- Microsoft
- Product
- Windows Server 2019
- Classifications
- CWE-122, T1068
- Attack vector
- local
- Privileges
- authenticated
Timeline
How it unfolded
- May 12, 2026CVE publishedPublication date reported by the CVE source.
- May 12, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=10.0.17763.0 <10.0.17763.8755
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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