EUVD-2026-56435
GHSA-4m39-8wrx-r248
Severity by source
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Local vector and low-privilege requirement are confirmed by description; full C/I/A reflects complete privilege escalation to SYSTEM; scope unchanged as exploitation is contained within the local system boundary.
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
Lifecycle Timeline
3DescriptionCVE.org
Heap-based buffer overflow in Windows Remote Access API allows an authorized attacker to elevate privileges locally.
AnalysisAI
Privilege escalation via heap buffer overflow in the Windows Remote Access (RAS) API affects every major in-support Windows desktop and server release, from Server 2012 R2 through Windows 11 26H1 and Server 2025. An authenticated local attacker with low-privileged access can trigger a CWE-122 heap overflow to achieve full SYSTEM-level compromise with High confidentiality, integrity, and availability impact and no user interaction required. No public exploit code or active exploitation has been identified at time of analysis; Microsoft has released a patch across all affected build lines.
Technical ContextAI
The vulnerability resides in the Windows Remote Access (RAS) API subsystem, a built-in Windows component providing programmatic interfaces for VPN, dial-up, and remote connection management, accessible to standard user-mode processes. CWE-122 (Heap-based Buffer Overflow) identifies the root cause as a write operation that exceeds the bounds of a heap-allocated buffer, likely triggered by passing malformed or oversized data to a RAS API function. Heap overflows in Windows API subsystems are classically leveraged to overwrite adjacent heap metadata, object vtable pointers, or free-list structures, redirecting execution into attacker-controlled memory at elevated privilege. The CVSS vector AV:L/AC:L/PR:L/UI:N/S:U confirms local access with a low-privileged account suffices and no user interaction is needed, placing this firmly in the local privilege escalation (LPE) class. Affected product scope spans Windows 10 versions 1607 through 22H2, Windows 11 versions 23H2 through 26H1, and Windows Server editions from 2012 R2 through 2025, including Server Core installations.
RemediationAI
Apply the Microsoft security update for CVE-2026-65671 through Windows Update, WSUS, or the Microsoft Update Catalog for all affected systems. Target build thresholds per release: Windows Server 2012 R2 to 6.3.9600.23337 or later; Windows 10/Server 2016 to 10.0.14393.9418 or later; Windows Server 2019/Windows 10 1809 to 10.0.17763.9115 or later; Windows 10 21H2 to 10.0.19044.7663 or later; Windows 10 22H2 to 10.0.19045.7663 or later; Windows Server 2022 to 10.0.20348.5499 or later; Windows 11 23H2 to 10.0.22631.7517 or later; Windows 11 24H2 and Server 2025 to 10.0.26100.9168/10.0.26100.33296 or later; Windows 11 25H2 to 10.0.26200.9168 or later; Windows 11 26H1 to 10.0.28000.2704 or later. See https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-65671 for the full advisory. Where patching cannot be immediately applied, restrict local logon and Remote Desktop rights to explicitly trusted administrative accounts via Group Policy (Computer Configuration > Windows Settings > Security Settings > Local Policies > User Rights Assignment > Allow log on locally / Allow log on through Remote Desktop Services), reducing the set of principals capable of reaching the vulnerable API. This compensating control does not eliminate the vulnerability but raises the pre-exploitation bar; it may impact legitimate user workflows on shared or multi-user systems and should be tested before broad deployment.
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Same weakness CWE-122 – Heap-based Buffer Overflow
View allSame technique Buffer Overflow
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External POC / Exploit Code
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