External risk intelligence

Windows ONCRPC XDR Driver Remote Code Execution

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2021-26432

The vulnerability affects the Network File System (NFS) service. NFS is designed for local area network file sharing and is typically restricted by firewalls or internal network segmentation. It is not intended for direct exposure to the public internet, making public-facing deployments uncommon in standard security practices.

Remote Code Execution

Microsoft Windows 10

20h221h11607180919092004r2

Halo Surface Signal: 2 out of 5 — less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

This vulnerability affects Windows Services for NFS, a component used for network file sharing. It allows for remote code execution, meaning an attacker could potentially run their own code on a vulnerable system without any user interaction. The main concern is confirming relevance and exposure, as NFS is not typically exposed to the internet.

A security flaw in Windows file sharing.
Could allow attackers to run code remotely.
Confirm if your Windows NFS services are exposed.

Attack Path

How an attacker could exploit the issue

An attacker could reach a vulnerable Windows system over the network and send a specially crafted request to the ONCRPC XDR driver. This could allow them to execute arbitrary code on the affected system, leading to a complete compromise.

No special access needed.
Triggered via network request.
Leads to remote code execution.

Live Threat

Current exploitation, exposure, and threat context

A critical vulnerability in the Windows Services for NFS ONCRPC XDR Driver could allow an unauthenticated attacker to execute arbitrary code remotely. This could enable the attacker to gain control of the affected system, potentially leading to data theft, system compromise, or further malicious activities. This vulnerability is externally accessible and does not require user interaction to be exploited.

System data and service behavior.
Remote code execution is possible.
Complete system control.

Operational Fix

Recommended remediation, mitigation, and detection steps

The Windows Services for NFS ONCRPC XDR Driver vulnerability requires immediate attention from teams managing Windows infrastructure. The initial focus should be on identifying all instances of the affected Windows operating systems, determining their network exposure and business criticality, and then pinpointing the accountable system or application owner to plan remediation.

Infrastructure and system owners.
Verify network exposure and criticality.
Plan and coordinate remediation actions.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is the Windows Services for NFS component?

It is a Microsoft feature that enables file sharing between Windows computers and other systems using the Network File System protocol. It is primarily used in enterprise environments to allow diverse operating systems to access files stored on Windows Servers. This vulnerability specifically affects the ONCRPC XDR driver, which handles how data is translated and exchanged during these network file requests across various Windows 10, 8.1, and Server editions.

How does CVE-2021-26432 allow remote code execution?

This vulnerability involves a weakness in how the ONCRPC XDR driver processes certain network data. When the driver fails to handle specific, malformed requests correctly, it can lead to memory corruption. An attacker who successfully sends these crafted requests can manipulate the system's execution flow, potentially allowing them to run their own commands or software with the privileges of the NFS service, bypassing the need for a legitimate login.

What is required to trigger this NFS driver vulnerability?

The flaw is triggered when a vulnerable system receives a specially crafted request over the network. Crucially, the attacker does not need any prior authentication or user interaction to send this request. Simply having the NFS service reachable and configured to listen for these specific RPC communications is enough; if the service is disabled or blocked at the network level, the attack path cannot be established.

Is my system at risk if it runs Windows Services for NFS?

Halo Surface Signal indicates that while the vulnerability is network-accessible, the risk depends heavily on your network architecture. NFS is designed for local area networks and should not be accessible from the public internet. If your systems are properly segmented and protected by firewalls, the likelihood of an external attacker reaching the service is significantly reduced compared to internet-facing infrastructure.

How should I respond to this vulnerability?

Your first step is to perform an inventory of your environment to identify any servers where Windows Services for NFS is actively running. Once you have a list of these systems, verify their network placement to confirm they are not exposed to untrusted networks. Coordinate with your infrastructure owners to prioritize patching these identified assets, as applying the appropriate vendor update is the most effective way to address the underlying driver flaw.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.