CVE-2025-39730 – This CVE is a Linux kernel vulnerability in the... (How to Fix)

Q: What is the severity of CVE-2025-39730?

CVE-2025-39730 has a CVSS score of 7.8 (HIGH). This CVE is a Linux kernel vulnerability in the NFS (Network File System) subsystem where insufficient bounds checking in the nfs_fh_to_dentry() function could allow attackers to trigger memory corruption. Systems running vulnerable Linux kernel versions with NFS enabled are affected. The vulnerability could lead to denial of service or potential privilege escalation.

📋 TL;DR

This CVE is a Linux kernel vulnerability in the NFS (Network File System) subsystem where insufficient bounds checking in the nfs_fh_to_dentry() function could allow attackers to trigger memory corruption. Systems running vulnerable Linux kernel versions with NFS enabled are affected. The vulnerability could lead to denial of service or potential privilege escalation.

💻 Affected Systems

Products:

Linux kernel

Versions: Specific vulnerable kernel versions referenced in the git commits (exact range requires checking each commit against kernel releases)

Operating Systems: Linux distributions using affected kernel versions

Default Config Vulnerable: ✅ No

Notes: Only vulnerable if NFS server or client functionality is enabled. Many systems have NFS disabled by default.

📦 What is this software?

Debian Linux by Debian

View all CVEs affecting Debian Linux →

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

Linux Kernel by Linux

The Linux Kernel is the core component of the Linux operating system, serving as the critical interface between computer hardware and software processes. As the heart of millions of servers, cloud infrastructure, embedded systems, Android devices, and IoT deployments worldwide, the Linux Kernel mana...

Learn more about Linux Kernel →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Kernel panic leading to system crash, or potential privilege escalation to root if combined with other vulnerabilities.

🟠

Likely Case

Denial of service through kernel panic or system instability when processing malformed NFS filehandles.

🟢

If Mitigated

Limited impact if NFS is disabled or proper network segmentation prevents access to NFS services.

🌐 Internet-Facing: MEDIUM - NFS services exposed to the internet could be targeted, but NFS is typically used internally.

🏢 Internal Only: HIGH - Internal attackers or compromised systems could exploit this to crash systems or potentially escalate privileges.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Exploitation requires ability to send malformed NFS filehandles to the target system, typically requiring some level of network access to NFS services.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Kernel versions containing the fixes from the provided git commits

Vendor Advisory: https://git.kernel.org/stable/c/12ad3def2e5e0b120e3d0cb6ce8b7b796819ad40

Restart Required: Yes

Instructions:

1. Update Linux kernel to patched version from your distribution's repositories. 2. Reboot system to load new kernel. 3. Verify kernel version after reboot.

🔧 Temporary Workarounds

Disable NFS services

linux

Disable NFS server and client functionality if not required

systemctl stop nfs-server
systemctl disable nfs-server
systemctl stop nfs-client.target
systemctl disable nfs-client.target

Restrict NFS network access

linux

Use firewall rules to limit NFS access to trusted networks only

iptables -A INPUT -p tcp --dport 2049 -s TRUSTED_NETWORK -j ACCEPT
iptables -A INPUT -p udp --dport 2049 -s TRUSTED_NETWORK -j ACCEPT
iptables -A INPUT -p tcp --dport 2049 -j DROP
iptables -A INPUT -p udp --dport 2049 -j DROP

🧯 If You Can't Patch

Disable NFS services completely if not required
Implement strict network segmentation to isolate NFS traffic to trusted zones only

🔍 How to Verify

Check if Vulnerable:

Check if NFS services are running and check kernel version against patched versions from your distribution

Check Version:

uname -r

Verify Fix Applied:

Verify kernel version after update and ensure NFS services function normally

📡 Detection & Monitoring

Log Indicators:

Kernel panic messages in /var/log/messages or dmesg
NFS error messages related to filehandle processing

Network Indicators:

Unusual NFS traffic patterns or malformed NFS requests

SIEM Query:

source="kernel" AND ("panic" OR "Oops") OR source="nfs" AND ("filehandle" OR "bounds")

📊 Metadata

CVE ID: CVE-2025-39730

CVSS v3 Score: 7.8 (HIGH)

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

EPSS Score: 0.01% exploit probability (1.7th percentile)

Published: September 7, 2025

Last Updated: January 12, 2026

🔗 References

https://git.kernel.org/stable/c/12ad3def2e5e0b120e3d0cb6ce8b7b796819ad40 Patch
https://git.kernel.org/stable/c/2ad40b7992aa26bc631afc1a995b0e3ddc30de3f Patch
https://git.kernel.org/stable/c/3570ef5c31314c13274c935a20b91768ab5bf412 Patch
https://git.kernel.org/stable/c/763810bb883cb4de412a72f338d80947d97df67b Patch
https://git.kernel.org/stable/c/7dd36f7477d1e03a1fcf8d13531ca326c4fb599f Patch
https://git.kernel.org/stable/c/7f8eca87fef7519e9c41f3258f25ebc2752247ee Patch
https://git.kernel.org/stable/c/b7f7866932466332a2528fda099000b035303485 Patch
https://git.kernel.org/stable/c/cb09afa0948d96b1e385d609ed044bb1aa043536 Patch
https://git.kernel.org/stable/c/ef93a685e01a281b5e2a25ce4e3428cf9371a205 Patch
https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html Third Party Advisory,Mailing List
https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html Third Party Advisory,Mailing List

📤 Share & Export

📄 Export Markdown 📋 Export JSON