CVE-2026-33840: Win32k Elevation of Privilege Vulnerability
CVE-2026-33840 is an elevation of privilege vulnerability in Win32k, rated Important by Microsoft, with a CVSS 3.1 base score of 7.8 (High). An attacker can exploit it by an attacker with local access, with low privileges and without user interaction. Microsoft has not reported exploitation in the wild and rates exploitation as more likely. The EPSS model estimates a 2.01% probability of exploitation activity in the next 30 days, higher than 81% of all scored vulnerabilities. Microsoft released the fix on 12 May 2026 in the May 2026 Patch Tuesday, delivered through 5 security updates (KB5087539, KB5087423, KB5089549, KB5089466 and more). It affects 8 products in 1 product family (Windows).
Key facts
- CVE ID
- CVE-2026-33840
- Severity
- High CVSS 7.8
- Microsoft severity
- Important
- Impact
- Elevation of Privilege
- Exploited in the wild
- No
- Publicly disclosed
- No
- Exploitation likelihood
- More Likely
- Weakness
- CWE-416
- EPSS
- 2.01% (percentile 81%)
- CISA KEV
- Not listed
- Released
- Last updated
- Patch Tuesday
- May 2026 Patch Tuesday
- Product families
- Windows
CVSS score and vector
Microsoft scores CVE-2026-33840 at 7.8 (temporal 6.8) using CVSS 3.1. Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
| Metric | Value |
|---|---|
| Attack vector | Local |
| Attack complexity | Low |
| Privileges required | Low |
| User interaction | None |
| Scope | Unchanged |
| Confidentiality impact | High |
| Integrity impact | High |
| Availability impact | High |
| Exploit code maturity | Unproven |
| Remediation level | Official fix |
| Report confidence | Confirmed |
Description
Use after free in Windows Win32K - ICOMP allows an authorized attacker to elevate privileges locally.
Frequently asked questions (Microsoft)
What privileges could be gained by an attacker who successfully exploited this vulnerability?
An attacker who successfully exploited this vulnerability could gain SYSTEM privileges.
Affected products (8)
Windows
| Product | Security update | Type | Fixed build | Restart |
|---|---|---|---|---|
| Windows Server 2025 (Server Core installation) | KB5087539 KB5087423 | Security Update Security Hotpatch Update | 10.0.26100.32860 10.0.26100.32772 | Yes Yes |
| Windows 11 Version 25H2 for ARM64-based Systems | KB5089549 KB5089466 | Security Update Security Hotpatch Update | 10.0.26200.8457 10.0.26200.8390 | Yes Yes |
| Windows 11 Version 25H2 for x64-based Systems | KB5089549 KB5089466 | Security Update Security Hotpatch Update | 10.0.26200.8457 10.0.26200.8390 | Yes Yes |
| Windows 11 Version 24H2 for ARM64-based Systems | ||||
| Windows 11 Version 24H2 for x64-based Systems | ||||
| Windows Server 2025 | KB5087539 KB5087423 | Security Update Security Hotpatch Update | 10.0.26100.32860 10.0.26100.32772 | Yes Yes |
| Windows 11 version 26H1 for x64-based Systems | KB5089548 | Security Update | 10.0.28000.2113 | Yes |
| Windows 11 Version 26H1 for ARM64-based Systems | KB5089548 | Security Update | 10.0.28000.2113 | Yes |
Security updates (5)
NIST NVD data
- NVD status
- Modified
- NVD CVSS
- 7.8 (HIGH)
- NVD weakness
- CWE-416
- Published to NVD
- NVD last modified
Affected configurations (CPE)
| Product | Vulnerable versions |
|---|---|
| windows 11 24h2 (arm64) | before 10.0.26100.8390 |
| windows 11 24h2 (x64) | before 10.0.26100.8390 |
| windows 11 25h2 (arm64) | before 10.0.26200.8390 |
| windows 11 25h2 (x64) | before 10.0.26200.8390 |
| windows 11 26h1 (arm64) | before 10.0.28000.2113 |
| windows 11 26h1 (x64) | before 10.0.28000.2113 |
| windows server 2025 | before 10.0.26100.32772 |
References
- https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-33840 (Vendor Advisory)
Acknowledgments
- DongJun Kim (smlijun) with UIUC
- Hwiwon Lee (hwiwonl) with UIUC
- Jongseong Kim (nevul37) with UIUC
- Kentaro Kawane with GMO Cybersecurity by Ierae, Inc.
- Minjea Park with Stealien
- Minjea Park, ji9umi and Jmini with Stealien
- Younggi Park (grill66) with UIUC
Revision history
| Version | Date | Description |
|---|---|---|
| 1.0 | Information published. | |
| 1.1 | Acknowledgement added. This is an informational change only. | |
| 1.2 | Updated an acknowledgement. This is an informational change only. |