CVE-2021-47496 – A Linux kernel vulnerability in the TLS impleme... (How to Fix)

Q: What is the severity of CVE-2021-47496?

CVE-2021-47496 has a CVSS score of 7.8 (HIGH). A Linux kernel vulnerability in the TLS implementation where incorrect error sign handling leads to memory corruption. This allows local attackers to potentially crash systems or execute arbitrary code. Affects systems running vulnerable Linux kernel versions with TLS enabled.

📋 TL;DR

A Linux kernel vulnerability in the TLS implementation where incorrect error sign handling leads to memory corruption. This allows local attackers to potentially crash systems or execute arbitrary code. Affects systems running vulnerable Linux kernel versions with TLS enabled.

💻 Affected Systems

Products:

Linux kernel

Versions: Kernel versions with the vulnerable TLS implementation (specific versions not provided in CVE description)

Operating Systems: Linux distributions using affected kernel versions

Default Config Vulnerable: ✅ No

Notes: Requires TLS kernel module to be loaded and used. Not all Linux systems have TLS enabled 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...

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

Local privilege escalation leading to full system compromise via arbitrary code execution or kernel panic causing denial of service.

🟠

Likely Case

System crash or kernel panic resulting in denial of service, potentially leading to data corruption.

🟢

If Mitigated

Limited impact if TLS is disabled or systems are properly patched.

🌐 Internet-Facing: LOW (requires local access to trigger)

🏢 Internal Only: MEDIUM (local attackers or malicious insiders could exploit)

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: UNKNOWN

Unauthenticated Exploit: ✅ No

Complexity: MEDIUM

Requires local access and ability to trigger TLS operations with specific error conditions.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: Kernel versions containing commit da353fac65fede6b8b4cfe207f0d9408e3121105 or later

Vendor Advisory: https://git.kernel.org/stable/c/da353fac65fede6b8b4cfe207f0d9408e3121105

Restart Required: Yes

Instructions:

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

🔧 Temporary Workarounds

Disable kernel TLS module

linux

Unload the TLS kernel module if not required

rmmod tls
echo 'blacklist tls' >> /etc/modprobe.d/blacklist.conf

🧯 If You Can't Patch

Disable TLS functionality in applications
Implement strict access controls to limit local user privileges

🔍 How to Verify

Check if Vulnerable:

Check if TLS module is loaded: lsmod | grep tls. If loaded and kernel version is unpatched, system is vulnerable.

Check Version:

uname -r

Verify Fix Applied:

Check kernel version after update and verify TLS module functions correctly with test connections.

📡 Detection & Monitoring

Log Indicators:

Kernel panic logs
System crash dumps
TLS connection failures with unusual error codes

Network Indicators:

Unexpected TLS connection resets
Abnormal termination of TLS sessions

SIEM Query:

Search for kernel panic events or TLS module errors in system logs

📊 Metadata

CVE ID: CVE-2021-47496

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

CWE: CWE-787

Published: May 22, 2024

Last Updated: September 24, 2025

🔗 References

📤 Share & Export

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🔗 Related Vulnerabilities

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