CVE-2022-21993: Windows 10 Information Disclosure Flaw

CVE-2022-21993 Overview

CVE-2022-21993 is an information disclosure vulnerability affecting the Windows Services for NFS ONCRPC XDR Driver. This vulnerability exists in the Open Network Computing Remote Procedure Call (ONCRPC) External Data Representation (XDR) driver component, which is responsible for handling data serialization in NFS (Network File System) communications. An attacker who successfully exploits this vulnerability could gain unauthorized access to sensitive information from affected Windows systems.

Critical Impact

This vulnerability allows remote attackers to disclose sensitive information from affected Windows systems without requiring authentication or user interaction. The network-accessible nature and lack of complexity make this a significant concern for enterprise environments using NFS services.

Affected Products

• Microsoft Windows 10 (multiple versions: 1607, 1809, 1909, 20H2, 21H1, 21H2 across x86, x64, and ARM64 architectures)
• Microsoft Windows 11 (x64 and ARM64)
• Microsoft Windows 8.1 (x86 and x64)
• Microsoft Windows RT 8.1
• Microsoft Windows Server 2012 and 2012 R2
• Microsoft Windows Server 2016
• Microsoft Windows Server 2019
• Microsoft Windows Server 20H2 and 2022

Discovery Timeline

• February 9, 2022 - CVE-2022-21993 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2022-21993

Vulnerability Analysis

The vulnerability resides in the ONCRPC XDR driver, a kernel-mode component that handles data representation translation for NFS operations in Windows. The XDR (External Data Representation) standard defines how data is serialized and deserialized when communicating between systems with potentially different architectures.

The information disclosure occurs due to improper handling of data within the XDR driver, which can result in the exposure of sensitive memory contents. Since the driver operates at the kernel level, the disclosed information could potentially include sensitive kernel memory data, credentials, or other confidential information processed by the system.

This vulnerability can be exploited remotely over the network without requiring authentication or any form of user interaction, making it particularly dangerous for systems with NFS services exposed to untrusted networks.

Root Cause

The root cause of this vulnerability stems from improper data handling within the ONCRPC XDR driver component. The driver fails to properly validate or sanitize data during XDR encoding and decoding operations, leading to information leakage. This type of vulnerability typically occurs when:

• Memory buffers are not properly initialized before use
• Response data includes unintended memory contents beyond the expected payload
• Error handling paths expose internal state or memory contents
• Boundary checks are insufficient during data serialization

Attack Vector

The attack vector for CVE-2022-21993 is network-based, meaning an attacker can exploit this vulnerability remotely by sending specially crafted NFS requests to a vulnerable system. The attack requires:

1. Network access to the target system's NFS service
2. The target system must have Windows Services for NFS enabled
3. No authentication is required to exploit the vulnerability
4. No user interaction is needed

An attacker would craft malicious ONCRPC requests designed to trigger the vulnerable code path in the XDR driver, causing the system to disclose sensitive information in its response. This information could be used for reconnaissance or to facilitate further attacks.

The vulnerability affects systems where the NFS client or server role is enabled, making file servers and systems participating in NFS-based file sharing particularly at risk.

Detection Methods for CVE-2022-21993

Indicators of Compromise

• Unusual NFS traffic patterns or malformed ONCRPC requests targeting Windows systems
• Unexpected network connections to NFS ports (TCP/UDP 2049) from unknown sources
• Anomalous response sizes from the NFS service indicating potential information leakage
• System event logs showing errors or warnings related to the nfssvr.sys or related NFS drivers

Detection Strategies

• Deploy network intrusion detection systems (NIDS) with signatures for anomalous NFS/ONCRPC traffic patterns
• Monitor Windows Security and System event logs for NFS-related errors or unexpected driver behavior
• Implement network traffic analysis to detect unusual data volumes in NFS responses
• Use endpoint detection and response (EDR) solutions to monitor for suspicious kernel driver activity

Monitoring Recommendations

• Enable detailed logging for Windows Services for NFS components
• Configure network monitoring to alert on NFS traffic from untrusted network segments
• Implement baseline analysis for NFS response sizes to detect anomalous information disclosure
• Deploy SentinelOne agents to provide real-time monitoring and behavioral analysis of NFS driver activity

How to Mitigate CVE-2022-21993

Immediate Actions Required

• Apply Microsoft security updates from February 2022 Patch Tuesday immediately
• If patching is not immediately possible, consider disabling Windows Services for NFS until patches can be applied
• Restrict network access to NFS services using firewall rules to trusted hosts only
• Segment NFS traffic to isolated network zones where possible

Patch Information

Microsoft has released security updates to address this vulnerability as part of the February 2022 security updates. Organizations should apply the appropriate patches for their Windows version through Windows Update, WSUS, or Microsoft Update Catalog.

For detailed patch information and download links, refer to the Microsoft Security Update Guide for CVE-2022-21993.

Workarounds

• Disable Windows Services for NFS if not required for business operations
• Implement strict firewall rules to limit NFS access to trusted IP addresses only
• Use network segmentation to isolate systems running NFS services from untrusted networks
• Consider using VPN or other secure tunneling for NFS traffic if cross-network access is required

# Disable NFS Client feature via PowerShell (requires admin privileges)
Disable-WindowsOptionalFeature -Online -FeatureName "ServicesForNFS-ClientOnly"

# Disable NFS Server feature via PowerShell (requires admin privileges)
Disable-WindowsOptionalFeature -Online -FeatureName "ServicesForNFS-ServerAndClient"

# Firewall rule to restrict NFS access (example - adjust as needed)
New-NetFirewallRule -DisplayName "Block External NFS" -Direction Inbound -LocalPort 2049 -Protocol TCP -Action Block -RemoteAddress "!10.0.0.0/8,!172.16.0.0/12,!192.168.0.0/16"