CVE-2021-47468 – This CVE describes a race condition vulnerabili... (How to Fix)

Q: What is the severity of CVE-2021-47468?

CVE-2021-47468 has a CVSS score of 5.5 (MEDIUM). This CVE describes a race condition vulnerability in the Linux kernel's mISDN subsystem where a sleeping function (card->isac.release()) is called from an atomic context while holding a lock. This can cause kernel panics or system crashes, affecting systems using ISDN hardware with the netjet driver.

📋 TL;DR

This CVE describes a race condition vulnerability in the Linux kernel's mISDN subsystem where a sleeping function (card->isac.release()) is called from an atomic context while holding a lock. This can cause kernel panics or system crashes, affecting systems using ISDN hardware with the netjet driver.

💻 Affected Systems

Products:

Linux kernel

Versions: Specific kernel versions with the vulnerable mISDN/netjet driver code (exact range depends on distribution backports)

Operating Systems: Linux distributions using affected kernel versions

Default Config Vulnerable: ✅ No

Notes: Only vulnerable if mISDN subsystem and netjet driver are loaded/used (typically requires specific ISDN hardware). Most systems won't have this loaded by default.

📦 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...

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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 →

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 causing data loss or service disruption.

🟠

Likely Case

System instability or crash when ISDN hardware is being removed or reconfigured, requiring reboot to restore service.

🟢

If Mitigated

Minor performance impact or no effect if ISDN hardware is not in use or properly configured.

🌐 Internet-Facing: LOW - Requires local access or specific hardware interaction, not directly exploitable over network.

🏢 Internal Only: MEDIUM - Local users or processes with hardware access could trigger the condition, causing system instability.

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: NO

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Exploitation requires triggering the specific race condition during hardware removal/configuration, typically requiring local access and specific hardware.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Fixed in kernel commits: 37e4f57b22cc5ebb3f80cf0f74fdeb487f082367 and related backports

Vendor Advisory: https://git.kernel.org/stable/c/37e4f57b22cc5ebb3f80cf0f74fdeb487f082367

Restart Required: Yes

Instructions:

1. Update Linux kernel to patched version from your distribution. 2. For custom kernels, apply the fix commit. 3. Reboot system to load new kernel.

🔧 Temporary Workarounds

Unload vulnerable driver

linux

Remove the netjet driver module if not needed

sudo rmmod netjet
sudo modprobe -r netjet

Blacklist driver

linux

Prevent netjet driver from loading automatically

echo 'blacklist netjet' | sudo tee /etc/modprobe.d/blacklist-netjet.conf

🧯 If You Can't Patch

Ensure netjet driver is not loaded (check with lsmod)
Avoid hot-plugging or reconfiguring ISDN hardware while system is running

🔍 How to Verify

Check if Vulnerable:

Check if netjet module is loaded: lsmod | grep netjet AND check kernel version against patched versions

Check Version:

uname -r

Verify Fix Applied:

Verify kernel version is patched AND netjet module loads without errors during hardware operations

📡 Detection & Monitoring

Log Indicators:

Kernel logs showing 'sleeping function called from invalid context'
System crashes during ISDN hardware operations

Network Indicators:

None - this is a local kernel issue

SIEM Query:

source="kernel" AND "sleeping function called from invalid context" AND "netjet"

📊 Metadata

CVE ID: CVE-2021-47468

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

CWE: CWE-667

Published: May 22, 2024

Last Updated: September 24, 2025

🔗 References

📤 Share & Export

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🔗 Related Vulnerabilities

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