CVE-2026-56647: Windows 10 1607 Privilege Escalation Flaw

CVE-2026-56647 Overview

CVE-2026-56647 is an integer overflow vulnerability [CWE-190] in the Windows Remote Access Service (RAS) Infrastructure. An authenticated attacker can exploit the flaw over a network to elevate privileges on affected Windows systems. The vulnerability affects a broad range of Microsoft desktop and server operating systems, including Windows 10, Windows 11, and Windows Server editions from 2012 through 2025. Microsoft published the advisory on July 14, 2026, and the issue carries a CVSS 3.1 base score of 8.8. Successful exploitation compromises confidentiality, integrity, and availability of the target host.

Critical Impact
An authorized attacker can trigger an integer overflow in Windows RAS Infrastructure over the network to gain elevated privileges, resulting in full compromise of confidentiality, integrity, and availability on affected systems.

Affected Products

Microsoft Windows 10 (versions 1607, 1809, 21H2, 22H2)
Microsoft Windows 11 (versions 24H2, 25H2, 26H1)
Microsoft Windows Server 2012, 2012 R2, 2016, 2019, 2022, and 2025

Discovery Timeline

2026-07-14 - CVE-2026-56647 published to NVD and Microsoft releases security update
2026-07-17 - Last updated in NVD database

Technical Details for CVE-2026-56647

Vulnerability Analysis

The vulnerability resides in the Windows Remote Access Service (RAS) Infrastructure, which handles inbound remote connectivity through protocols such as VPN and dial-up. An attacker who has already authenticated to the target environment can send crafted network input that triggers an integer overflow or wraparound during RAS processing. The arithmetic error causes the service to miscalculate buffer sizes or index values, corrupting adjacent memory structures. This corruption enables the attacker to elevate privileges beyond the level granted by their initial authenticated context. The Exploit Prediction Scoring System (EPSS) currently rates the vulnerability at 0.852 percent, though the exposure on domain-joined and remote-access-enabled hosts makes it a priority for patching.

Root Cause

The root cause is an integer overflow condition [CWE-190] in code paths responsible for parsing or handling RAS protocol data. When a specially crafted value exceeds the maximum representable size of the integer type, the arithmetic wraps around to an unexpectedly small value. Subsequent memory allocations or length checks operate on the wrapped value, permitting out-of-bounds writes or logic bypasses within the RAS service context.

Attack Vector

The attack is executed over the network and requires low privileges but no user interaction. An authenticated attacker sends malicious traffic to a system exposing RAS Infrastructure. Because RAS commonly runs with elevated service privileges, successful exploitation grants the attacker higher-privileged code execution on the target. The scope remains unchanged, but the impact on confidentiality, integrity, and availability is high.

No verified public proof-of-concept exploit code is available at this time. Refer to the Microsoft Security Update CVE-2026-56647 advisory for authoritative technical details.

Detection Methods for CVE-2026-56647

Indicators of Compromise

Unexpected crashes, restarts, or memory faults in Windows RAS-related services and processes such as svchost.exe hosting RasMan or RemoteAccess.
New or unexplained privileged accounts, scheduled tasks, or services created shortly after inbound RAS or VPN connections.
Anomalous inbound network traffic to RAS, VPN, or PPP-related endpoints from authenticated but low-privileged accounts.

Detection Strategies

Monitor Windows Event Logs for RAS service errors, access violations, and abnormal termination events on hosts running Routing and Remote Access.
Deploy behavioral endpoint identification to flag privilege escalation patterns originating from network service processes.
Correlate authentication logs with subsequent process-creation events under SYSTEM or service accounts to identify escalation chains.

Monitoring Recommendations

Enable verbose auditing on RAS servers and forward logs to a centralized SIEM for correlation across the fleet.
Track process token elevation events (Event ID 4672) generated by RAS-adjacent processes.
Baseline normal RAS connection volume and alert on statistical anomalies from authenticated internal sources.

How to Mitigate CVE-2026-56647

Immediate Actions Required

Apply the July 2026 Microsoft security updates to all affected Windows client and server systems without delay.
Prioritize patching on internet-exposed and internal servers running the Routing and Remote Access role.
Audit accounts with network access to RAS infrastructure and enforce least-privilege access controls.

Patch Information

Microsoft has released security updates addressing CVE-2026-56647 across all affected Windows versions. Full patch details, KB article numbers, and download links are available in the Microsoft Security Update Guide for CVE-2026-56647. Administrators should validate patch deployment through Windows Update, WSUS, or their configuration management platform.

Workarounds

Disable the Routing and Remote Access Service (RemoteAccess) on systems that do not require it.
Restrict network access to RAS endpoints using host-based firewall rules and network segmentation.
Require multi-factor authentication and strong credential hygiene for any account that can reach RAS services.

bash

# Disable the Routing and Remote Access service on systems that do not need it
sc.exe config RemoteAccess start= disabled
sc.exe stop RemoteAccess

# Block inbound PPTP/L2TP where RAS is not required
netsh advfirewall firewall add rule name="Block PPTP Inbound" dir=in action=block protocol=TCP localport=1723
netsh advfirewall firewall add rule name="Block L2TP Inbound" dir=in action=block protocol=UDP localport=1701