CVE-2025-21823 – A race condition vulnerability in the Linux ker... (How to Fix)

Q: What is the severity of CVE-2025-21823?

CVE-2025-21823 has a CVSS score of 5.5 (MEDIUM). A race condition vulnerability in the Linux kernel's batman-adv module could lead to memory corruption or kernel crashes. This affects systems using batman-adv for mesh networking, potentially causing denial of service or system instability. The vulnerability stems from improper handling of worker threads during interface removal.

📋 TL;DR

A race condition vulnerability in the Linux kernel's batman-adv module could lead to memory corruption or kernel crashes. This affects systems using batman-adv for mesh networking, potentially causing denial of service or system instability. The vulnerability stems from improper handling of worker threads during interface removal.

💻 Affected Systems

Products:

Linux kernel with batman-adv module

Versions: Specific kernel versions with vulnerable batman-adv implementation (check git commits for exact ranges)

Operating Systems: Linux distributions with vulnerable kernel versions

Default Config Vulnerable: ✅ No

Notes: Only vulnerable when batman-adv module is loaded and configured for mesh networking.

📦 What is this software?

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

Kernel panic leading to system crash and denial of service, potentially requiring physical intervention to restore functionality.

🟠

Likely Case

System instability, kernel crashes, or memory corruption when batman-adv interfaces are removed or reconfigured.

🟢

If Mitigated

Minor performance impact during interface changes with proper patching.

🌐 Internet-Facing: LOW - Requires local access or specific mesh network configuration.

🏢 Internal Only: MEDIUM - Affects systems using batman-adv mesh networking internally.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Requires ability to modify network interfaces or trigger batman-adv cleanup operations.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Kernel versions containing commits: 0fdc3c166ac17b26014313fa2b93696354511b24, 1c334629176c2d644befc31a20d4bf75542f7631, 3c0e0aecb78cb2a2ca1dc701982d08fedb088dc6, 781a06fd265a8151f7601122d9c2e985663828ff, 8c8ecc98f5c65947b0070a24bac11e12e47cc65d

Vendor Advisory: https://git.kernel.org/stable/c/0fdc3c166ac17b26014313fa2b93696354511b24

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 batman-adv module

linux

Unload batman-adv module if not required for system functionality

sudo modprobe -r batman_adv

Blacklist batman-adv module

linux

Prevent batman-adv module from loading at boot

echo 'blacklist batman_adv' | sudo tee /etc/modprobe.d/blacklist-batman-adv.conf

🧯 If You Can't Patch

Avoid removing or reconfiguring batman-adv interfaces while system is operational
Implement monitoring for kernel crashes or system instability related to network changes

🔍 How to Verify

Check if Vulnerable:

Check if batman-adv module is loaded: lsmod | grep batman_adv

Check Version:

uname -r

Verify Fix Applied:

Check kernel version includes fix commits: uname -r and verify with distribution patch notes

📡 Detection & Monitoring

Log Indicators:

Kernel panic messages
OOPs (kernel crashes) in dmesg
batman-adv related errors in system logs

Network Indicators:

Sudden loss of mesh network connectivity
Interface configuration failures

SIEM Query:

search 'kernel panic' OR 'Oops' OR 'batman_adv' in system logs

📊 Metadata

CVE ID: CVE-2025-21823

CVSS v3 Score: 5.5 (MEDIUM)

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

EPSS Score: 0.05% exploit probability (16.4th percentile)

Published: February 27, 2025

Last Updated: November 3, 2025

🔗 References

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