CVE-2026-62743 Overview
CVE-2026-62743 is an out-of-bounds read vulnerability in the Windows Win32k kernel-mode component. An authenticated local attacker can trigger the flaw to read memory outside the intended buffer boundaries. Successful exploitation results in the disclosure of kernel memory contents to a low-privileged process.
Microsoft published the advisory on August 11, 2026. The weakness is tracked under CWE-125: Out-of-bounds Read. The vulnerability requires local access and low privileges, and it does not require user interaction. The impact is limited to confidentiality; integrity and availability are not affected.
Critical Impact
Disclosed kernel memory can expose pointers, tokens, and cryptographic material that attackers chain with other flaws to bypass Kernel Address Space Layout Randomization (KASLR) and escalate privileges.
Affected Products
- Microsoft Windows 10 (1607, 1809, 21H2, 22H2)
- Microsoft Windows 11 (23H2, 24H2, 25H2, 26H1)
- Microsoft Windows Server 2012, 2012 R2, 2016, 2019, 2022, and 2025
Discovery Timeline
- 2026-08-11 - CVE-2026-62743 published to NVD
- 2026-08-11 - Microsoft releases security update via the Microsoft Security Update Guide
- 2026-08-13 - Last updated in NVD database
Technical Details for CVE-2026-62743
Vulnerability Analysis
The flaw resides in Win32k, the kernel-mode driver that implements the Windows graphical subsystem and window manager. Win32k exposes system calls that handle user-mode structures such as windows, menus, and device contexts. An out-of-bounds read [CWE-125] occurs when the driver reads past the end of an allocated buffer while processing one of these objects.
A local attacker with a standard user account invokes the vulnerable syscall with crafted parameters. The driver returns memory contents adjacent to the target buffer. These bytes can contain kernel pointers, object headers, or data from other processes. Attackers typically pair Win32k information disclosures with a separate memory corruption bug to defeat KASLR and achieve SYSTEM-level code execution.
Root Cause
The root cause is a missing or incorrect bounds check on an index or length field controlled by user-mode input. When the driver dereferences the value, it reads beyond the intended object. The condition is deterministic and does not depend on race windows or heap grooming.
Attack Vector
Exploitation requires local code execution in the context of an authenticated user. Remote exploitation is not possible without a prior foothold. The attacker calls the affected Win32k interface directly through a native API or graphics-related syscall. No user interaction is required beyond running the attacker's process.
No public proof-of-concept code is available at the time of publication, and the vulnerability is not listed on the CISA Known Exploited Vulnerabilities catalog. The EPSS estimate is 0.397%.
Detection Methods for CVE-2026-62743
Indicators of Compromise
- Unsigned or unusual binaries loading user32.dll and gdi32.dll while making direct syscalls into win32k.sys or win32kfull.sys.
- Standard-user processes accessing kernel objects or handles inconsistent with their normal behavior.
- Crash dumps referencing Win32k with PAGE_FAULT_IN_NONPAGED_AREA or bugcheck codes tied to graphics syscalls.
Detection Strategies
- Hunt for local processes making anomalous NtUserCall* or NtGdi* syscall sequences from non-graphical applications.
- Correlate Sysmon Event ID 10 (ProcessAccess) and Event ID 8 (CreateRemoteThread) with subsequent privilege changes on the host.
- Use behavioral AI-driven endpoint protection, such as Singularity Endpoint, to flag low-privileged processes that read kernel-derived pointers or attempt token manipulation after suspicious syscalls.
Monitoring Recommendations
- Enable kernel-mode driver telemetry and forward Windows Defender Exploit Guard logs to a centralized data lake for retrospective hunting.
- Baseline typical Win32k syscall patterns for line-of-business applications and alert on statistical outliers.
- Track patch-compliance for Windows 10, Windows 11, and Windows Server hosts through configuration management to confirm the August 2026 update is applied.
How to Mitigate CVE-2026-62743
Immediate Actions Required
- Apply the August 2026 Microsoft security update referenced in the Microsoft Security Update Guide to all affected Windows and Windows Server systems.
- Prioritize multi-user hosts, terminal servers, and jump boxes where local authenticated access is broadly available.
- Restrict interactive logon rights on servers to reduce the population of accounts that can reach the local attack surface.
Patch Information
Microsoft addressed CVE-2026-62743 in the cumulative updates released on August 11, 2026 for Windows 10, Windows 11, and Windows Server 2012 through 2025. Administrators should retrieve the appropriate KB package for each build from Windows Update, WSUS, or the Microsoft Update Catalog. The advisory is available in the Microsoft Security Update Guide.
Workarounds
- No official workaround exists; patching is the only supported remediation.
- Enforce least-privilege policies and remove local administrator rights from standard users to limit downstream impact if information disclosure is chained.
- Enable Windows Defender Credential Guard and Hypervisor-protected Code Integrity (HVCI) to reduce the value of leaked kernel data for privilege escalation.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
