CVE-2026-56650 Overview
CVE-2026-56650 is a heap-based buffer overflow [CWE-122] in the Windows Network File System (NFS) component. An authorized local attacker can exploit the flaw to elevate privileges on affected Windows client and server systems. The vulnerability affects a broad range of Microsoft Windows versions, spanning Windows 10, Windows 11, and Windows Server editions from 2012 through 2025.
Successful exploitation grants the attacker high impact on confidentiality, integrity, and availability. Microsoft published the advisory through the Microsoft Security Response Center (MSRC).
Critical Impact
A low-privileged local user can trigger the heap overflow within the NFS service to gain elevated privileges, achieving full compromise of the affected host.
Affected Products
- Microsoft Windows 10 (versions 1607, 1809, 21H2, 22H2) across x86, x64, and ARM64
- Microsoft Windows 11 (versions 24H2, 25H2, 26H1) across x64 and ARM64
- Microsoft Windows Server 2012, 2012 R2, 2016, 2019, 2022, and 2025
Discovery Timeline
- 2026-07-14 - CVE-2026-56650 published to NVD
- 2026-07-17 - Last updated in NVD database
Technical Details for CVE-2026-56650
Vulnerability Analysis
The vulnerability resides in the Windows Network File System implementation, which provides file sharing services compatible with the NFS protocol. A heap-based buffer overflow occurs when the NFS component processes attacker-influenced data without adequately validating the size against the destination buffer allocated on the heap.
Because the attack vector is local and requires low privileges with no user interaction, an authenticated user on the target system can trigger the overflow through crafted requests to the NFS service. Successful exploitation corrupts adjacent heap structures, enabling the attacker to influence control flow and execute code in the security context of the vulnerable service.
The outcome is a full privilege escalation with high confidentiality, integrity, and availability impact on the affected host.
Root Cause
The root cause is classified as [CWE-122] Heap-based Buffer Overflow. The NFS service copies input into a heap-allocated buffer without enforcing correct bounds. Attacker-controlled input therefore writes past the buffer boundary, corrupting heap metadata or adjacent objects.
Attack Vector
Exploitation requires local access with low privileges. The attacker interacts with the Windows NFS service on the local system to trigger the malformed input path. No user interaction is required, and the attack does not cross a scope boundary. On unpatched hosts where the NFS role or client is enabled, this creates a reliable local privilege escalation primitive.
No public proof-of-concept exploit or in-the-wild exploitation has been reported at the time of publication. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog.
Detection Methods for CVE-2026-56650
Indicators of Compromise
- Unexpected crashes or restarts of NfsService, NfsClnt, or related NFS driver components in the Windows event log.
- Creation of new high-privilege processes (for example, SYSTEM-context shells) as immediate children of NFS service processes.
- Anomalous local NFS RPC traffic originating from standard user accounts that do not normally interact with NFS.
Detection Strategies
- Monitor Windows Event Log channels for Application Error events (Event ID 1000) referencing NFS binaries such as nfssvc.exe or nfsclnt.exe.
- Correlate NFS service faults with subsequent token elevation, process injection, or unusual child process creation from NFS-related parents.
- Deploy endpoint identification and response tooling capable of behavioral analysis to flag privilege escalation chains originating from service processes.
Monitoring Recommendations
- Enable command-line auditing (Event ID 4688) and Sysmon process creation logging to capture process ancestry linked to NFS components.
- Track changes to accounts, group memberships, and scheduled tasks immediately following NFS service instability.
- Alert on installation of new services or drivers on hosts running the Server for NFS role.
How to Mitigate CVE-2026-56650
Immediate Actions Required
- Apply the Microsoft security update referenced in the Microsoft Security Update Guide for CVE-2026-56650 on all affected Windows client and server systems.
- Inventory hosts with the Server for NFS role or NFS client feature enabled and prioritize patching those systems first.
- Restrict local logon rights on servers running NFS services to trusted administrators only.
Patch Information
Microsoft has released security updates addressing CVE-2026-56650 for all supported Windows 10, Windows 11, and Windows Server versions listed in the advisory. Refer to the Microsoft Security Update Guide for the exact KB numbers and download links matching each build.
Workarounds
- Disable the Server for NFS role on Windows Server systems where NFS file sharing is not required, using Uninstall-WindowsFeature FS-NFS-Service.
- Disable the Client for NFS feature on Windows 10 and Windows 11 endpoints that do not need to mount NFS shares.
- Enforce least privilege on affected hosts and remove interactive logon capability for standard users on NFS-enabled servers.
# Configuration example: disable NFS server and client roles on Windows
Uninstall-WindowsFeature -Name FS-NFS-Service -Remove
Disable-WindowsOptionalFeature -Online -FeatureName ServicesForNFS-ClientOnly
Disable-WindowsOptionalFeature -Online -FeatureName ClientForNFS-Infrastructure
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
