CVE-2025-39839 – This vulnerability in the Linux kernel's batman... (How to Fix)

Q: What is the severity of CVE-2025-39839?

CVE-2025-39839 has a CVSS score of 7.1 (HIGH). This vulnerability in the Linux kernel's batman-adv network coding module allows out-of-bounds memory read/write operations. Attackers could potentially crash systems, leak sensitive information, or execute arbitrary code. Systems using batman-adv mesh networking with network coding enabled are affected.

📋 TL;DR

This vulnerability in the Linux kernel's batman-adv network coding module allows out-of-bounds memory read/write operations. Attackers could potentially crash systems, leak sensitive information, or execute arbitrary code. Systems using batman-adv mesh networking with network coding enabled are affected.

💻 Affected Systems

Products:

Linux kernel with batman-adv module

Versions: Specific kernel versions with vulnerable batman-adv commits; check git references for exact ranges

Operating Systems: Linux distributions using affected kernel versions

Default Config Vulnerable: ✅ No

Notes: Requires batman-adv mesh networking with network coding feature enabled (not default).

📦 What is this software?

Debian Linux by Debian

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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...

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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...

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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 →

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

Remote code execution leading to full system compromise, kernel panic causing denial of service, or sensitive kernel memory disclosure.

🟠

Likely Case

Kernel panic leading to system crash/reboot, memory corruption causing instability, or information disclosure from kernel memory.

🟢

If Mitigated

Denial of service through kernel panic if exploit attempts are blocked or fail.

🌐 Internet-Facing: MEDIUM - Requires batman-adv mesh networking with network coding enabled, which is less common in internet-facing systems.

🏢 Internal Only: MEDIUM - Internal systems using batman-adv mesh networking with network coding enabled are vulnerable to internal attackers.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ⚠️ Yes

Complexity: MEDIUM

Exploitation requires network access to batman-adv mesh and network coding enabled. No public exploit code known at this time.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Kernel versions with fixes from git references: 1e36c6c8dc8023b4bbe9a16e819f9998b9b6a183, 20080709457bc1e920eb002483d7d981d9b2ac1c, 30fc47248f02b8a14a61df469e1da4704be1a19f, 5d334bce9fad58cf328d8fa14ea1fff855819863, a67c6397fcb7e842d3c595243049940970541c48

Vendor Advisory: https://git.kernel.org/stable/c/1e36c6c8dc8023b4bbe9a16e819f9998b9b6a183

Restart Required: Yes

Instructions:

1. Update Linux kernel to patched version from your distribution. 2. Reboot system to load new kernel. 3. Verify batman-adv module loads correctly.

🔧 Temporary Workarounds

Disable network coding in batman-adv

linux

Disable the network coding feature in batman-adv to prevent exploitation

echo 0 > /sys/class/net/<batman-interface>/mesh/network_coding

Unload batman-adv module

linux

Remove the vulnerable module if not needed

modprobe -r batman_adv

🧯 If You Can't Patch

Disable batman-adv network coding feature on all interfaces
Implement network segmentation to isolate batman-adv mesh networks

🔍 How to Verify

Check if Vulnerable:

Check if batman-adv module is loaded and network coding is enabled: lsmod | grep batman_adv && cat /sys/class/net/*/mesh/network_coding 2>/dev/null

Check Version:

uname -r

Verify Fix Applied:

Check kernel version is patched: uname -r and verify with distribution's security advisories

📡 Detection & Monitoring

Log Indicators:

Kernel panic messages
batman-adv error logs
system crash/reboot logs

Network Indicators:

Unusual batman-adv packet patterns
Network coding protocol anomalies

SIEM Query:

source="kernel" AND ("panic" OR "oops" OR "batman-adv")

📊 Metadata

CVE ID: CVE-2025-39839

CVSS v3 Score: 7.1 (HIGH)

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

CWE: CWE-125

EPSS Score: 0.02% exploit probability (5.3th percentile)

Published: September 19, 2025

Last Updated: January 20, 2026

🔗 References

https://git.kernel.org/stable/c/1e36c6c8dc8023b4bbe9a16e819f9998b9b6a183 Patch
https://git.kernel.org/stable/c/20080709457bc1e920eb002483d7d981d9b2ac1c Patch
https://git.kernel.org/stable/c/30fc47248f02b8a14a61df469e1da4704be1a19f Patch
https://git.kernel.org/stable/c/5d334bce9fad58cf328d8fa14ea1fff855819863 Patch
https://git.kernel.org/stable/c/a67c6397fcb7e842d3c595243049940970541c48 Patch
https://git.kernel.org/stable/c/bb37252c9af1cb250f34735ee98f80b46be3cef1 Patch
https://git.kernel.org/stable/c/d77b6ff0ce35a6d0b0b7b9581bc3f76d041d4087 Patch
https://git.kernel.org/stable/c/dce6c2aa70e94c04c523b375dfcc664d7a0a560a 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

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