CVE-2023-24939 – CVE-2023-24939 is a denial-of-service vulnerabi... (How to Fix)

Q: What is the severity of CVE-2023-24939?

CVE-2023-24939 has a CVSS score of 7.5 (HIGH). CVE-2023-24939 is a denial-of-service vulnerability in Microsoft's Server for NFS (Network File System) that allows attackers to crash the service by sending specially crafted requests. This affects Windows Server systems with the Server for NFS role enabled. The vulnerability requires network access to the NFS service.

📋 TL;DR

CVE-2023-24939 is a denial-of-service vulnerability in Microsoft's Server for NFS (Network File System) that allows attackers to crash the service by sending specially crafted requests. This affects Windows Server systems with the Server for NFS role enabled. The vulnerability requires network access to the NFS service.

💻 Affected Systems

Products:

Microsoft Windows Server

Versions: Windows Server 2022, Windows Server 2019, Windows Server 2016

Operating Systems: Windows Server

Default Config Vulnerable: ✅ No

Notes: Only vulnerable when Server for NFS role is installed and enabled. Not all Windows Server installations have this role.

📦 What is this software?

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete unavailability of NFS file services, disrupting file access for all clients and potentially affecting dependent applications.

🟠

Likely Case

Service crashes requiring manual restart, causing temporary file access disruption for NFS clients.

🟢

If Mitigated

Minimal impact with proper network segmentation and monitoring allowing quick service restoration.

🌐 Internet-Facing: MEDIUM - While NFS services are typically internal, misconfigured internet-facing instances could be exploited.

🏢 Internal Only: HIGH - Internal attackers or compromised systems on the network can easily exploit this to disrupt file services.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Microsoft rates this as 'Exploitation More Likely' in their advisory. The vulnerability requires network access to the NFS service port (typically 2049).

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Apply the May 2023 security updates or later

Vendor Advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-24939

Restart Required: Yes

Instructions:

1. Install May 2023 Windows Server security updates via Windows Update. 2. Alternatively, download and install the standalone security update from Microsoft Update Catalog. 3. Restart the server to complete the installation.

🔧 Temporary Workarounds

Disable Server for NFS

windows

Remove or disable the Server for NFS role if not required

Remove-WindowsFeature FS-NFS-Service

Network Segmentation

windows

Restrict access to NFS port (2049) using firewall rules

New-NetFirewallRule -DisplayName 'Block NFS' -Direction Inbound -LocalPort 2049 -Protocol TCP -Action Block

🧯 If You Can't Patch

Implement strict network access controls to limit which systems can reach the NFS service
Monitor NFS service health and implement automated restart procedures for service crashes

🔍 How to Verify

Check if Vulnerable:

Check if Server for NFS is installed: Get-WindowsFeature FS-NFS-Service | Select-Object Installed. If installed and not patched with May 2023 updates, system is vulnerable.

Check Version:

systeminfo | findstr /B /C:"OS Name" /C:"OS Version"

Verify Fix Applied:

Verify Windows Update history shows May 2023 security updates installed and check NFS service version.

📡 Detection & Monitoring

Log Indicators:

Event ID 7034 in System logs indicating NFS service crashes
Unexpected NFS service restarts in application logs

Network Indicators:

Multiple connection attempts to port 2049 followed by service unavailability
Unusual NFS protocol traffic patterns

SIEM Query:

source="windows" event_id=7034 AND service_name="NfsSvr"

📊 Metadata

CVE ID: CVE-2023-24939

CVSS v3 Score: 7.5 (HIGH)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Published: May 9, 2023

Last Updated: November 21, 2024

🔗 References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-24939 Patch,Vendor Advisory
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2023-24939 Patch,Vendor Advisory

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📋 TL;DR

💻 Affected Systems

📦 What is this software?

Windows 10 1507 by Microsoft

Windows 10 1607 by Microsoft

Windows 10 1809 by Microsoft

Windows 10 20h2 by Microsoft

Windows 10 21h2 by Microsoft

Windows 10 22h2 by Microsoft

Windows 11 21h2 by Microsoft

Windows 11 22h2 by Microsoft

Windows Server 2012 by Microsoft