CVE-2026-56647

What it actually does

This vulnerability is an integer overflow or wraparound flaw in the Windows Remote Access Service infrastructure. A low-privileged, authenticated attacker with network access can trigger memory corruption in the affected service path and elevate privileges on a vulnerable Windows system. Because the CVSS vector indicates network access, low privileges, no user interaction, and high confidentiality, integrity, and availability impact, successful exploitation could allow the attacker to execute privileged actions, access sensitive data, modify system state, or disrupt the host. The issue affects multiple supported Windows client and server versions, including Windows 10, Windows 11, Windows Server 2012, 2016, 2019, 2022, and 2025 families.

Why it matters to the business

Successful exploitation could turn a limited authenticated foothold into administrative control of an affected Windows host or server. In practice, this may enable lateral movement, credential theft, tampering with business systems, deployment of additional malware, or service disruption. The vulnerability is not currently listed in CISA KEV, is not marked as used in ransomware campaigns, and has low EPSS at this time, but the broad Windows client and server exposure means organizations should still prioritize patching, especially on systems running Remote Access, VPN, routing, or remote connectivity services.

How an attack unfolds

An attacker first obtains valid low-privileged credentials or access to an account capable of reaching the affected Windows Remote Access Service infrastructure over the network. The attacker then sends crafted network input that causes an integer overflow or wraparound in the vulnerable service code path. If exploitation is successful, the arithmetic error leads to memory corruption and the attacker gains elevated privileges on the target system. From there, the attacker may create or modify accounts, dump credentials, disable security controls, install persistence, move laterally to other Windows systems, or disrupt Remote Access and related networking services. No public exploit maturity is currently indicated, so defenders should focus on exposure reduction, patch validation, and monitoring for anomalous authenticated access to Remote Access Service components.

How to fix it

Apply the Microsoft security update that addresses CVE-2026-56647 for all affected Windows versions as soon as it is available through Windows Update, Microsoft Update Catalog, WSUS, Intune, Configuration Manager, or the organization’s standard patch management platform. Because no exact fixed build numbers were provided in the input, administrators should verify remediation against Microsoft’s official security update guidance for the affected Windows release and servicing channel. Prioritize servers and clients that run or expose Remote Access, Routing and Remote Access Service, VPN, dial-up, DirectAccess, or related remote connectivity roles. If immediate patching is not possible, reduce exposure by disabling unused Remote Access/RRAS functionality, restricting network access to the service to trusted management or VPN networks, enforcing least privilege for accounts that can access the service, monitoring authenticated remote access attempts, and applying host-based firewall rules to limit reachable attack surface.

How to confirm the fix worked

Confirm that each affected Windows system has installed the Microsoft security update that includes the fix for this vulnerability. Validate through Windows Update history, Microsoft Update Catalog KB applicability, endpoint management compliance reports, or PowerShell-based inventory of installed hotfixes and OS build numbers. Confirm that vulnerable Remote Access, RRAS, VPN, or routing roles are disabled where not required. From a network perspective, verify that only approved systems can reach Remote Access-related services and that unnecessary inbound exposure is blocked by host and network firewalls. For high-risk servers, perform authenticated configuration review and vulnerability scanning after patch deployment to confirm the system no longer reports exposure.

Typical attack path

1. Identify Windows hosts exposing Remote Access Service, Routing and Remote Access, VPN, or related remote connectivity functionality.
2. Obtain or reuse valid low-privileged credentials through phishing, password spraying, credential theft, or prior compromise.
3. Authenticate to the vulnerable service over the network.
4. Send crafted requests that trigger the integer overflow or wraparound condition in the Windows Remote Access Service infrastructure.
5. Achieve elevated privileges on the target host if memory corruption is successfully exploited.
6. Use elevated access to run commands, access sensitive files, dump credentials, modify configuration, or disable defenses.
7. Expand access by moving laterally to other Windows systems or by establishing persistence.

How to detect it

To determine whether exploitation may have already occurred, review Windows event logs, Remote Access/RRAS operational logs, VPN or remote access appliance logs if applicable, endpoint detection telemetry, and authentication logs for suspicious low-privileged accounts connecting to Remote Access services followed by privilege escalation or administrative activity. Key sources include Windows Security logs, System logs, Microsoft-Windows-RemoteAccess logs, Microsoft-Windows-Ras* logs, PowerShell logs, Sysmon logs, EDR process telemetry, service creation events, account management events, and firewall logs. Look for sequences where a normal user authenticates remotely, Remote Access or RRAS components crash or restart, and the same host or account then performs privileged actions such as creating local administrators, installing services, dumping credentials, disabling security tools, or opening unusual outbound connections. Also investigate unexpected restarts of Remote Access-related services, application crash events involving RAS/RRAS binaries, anomalous network traffic to remote access services from internal hosts, and signs of lateral movement after remote access authentication. There are no known public exploit-specific indicators provided, so detection should focus on behavioral evidence of authenticated network exploitation and post-exploitation activity.

• RemoteAccess
• Remote Access Connection Manager
• RasMan
• Routing and Remote Access
• RemoteAccess-Service
• Microsoft-Windows-RemoteAccess
• Microsoft-Windows-RasClient
• Microsoft-Windows-RasServer
• svchost.exe -k netsvcs
• C:\Windows\System32\rasmans.dll
• C:\Windows\System32\mprdim.dll
• C:\Windows\System32\rrasmgmt.msc
• Event ID 7031
• Event ID 7034
• Event ID 4624
• Event ID 4672
• Event ID 4720
• Event ID 4732
• Event ID 4697
• Event ID 7045
• Event ID 4688
• wevtutil cl Security
• net localgroup administrators
• sc create
• powershell.exe -enc
• rundll32.exe comsvcs.dll, MiniDump

What your security team should do

• Prioritize patching for Windows servers and clients that run Remote Access, RRAS, VPN, DirectAccess, or routing functionality.
• Inventory affected Windows 10, Windows 11, and Windows Server versions and map them to the correct Microsoft security updates for their servicing channels.
• Restrict network access to Remote Access Service infrastructure to trusted administrative or remote-access networks only.
• Disable Remote Access, RRAS, VPN, dial-up, or routing roles on systems that do not require them.
• Review low-privileged accounts with remote access capability and remove unnecessary access.
• Monitor for unusual authenticated connections to Remote Access or RRAS services, especially from newly observed hosts or accounts.
• Hunt for post-exploitation behavior such as unexpected privilege changes, new local administrators, suspicious service creation, credential dumping, or security tool tampering.
• Because the issue is not currently in KEV and EPSS is low, treat this as a high-impact patching priority rather than confirmed active exploitation, unless local telemetry indicates suspicious activity.