CVE-2021-35039 : Exploit Details and Defense Strategies

A detailed overview of CVE-2021-35039, a vulnerability in the Linux kernel before version 5.12.14 that mishandles Signature Verification.

Understanding CVE-2021-35039

In this section, we will explore what CVE-2021-35039 is, its impact, technical details, and mitigation strategies.

What is CVE-2021-35039?

The vulnerability in the Linux kernel before version 5.12.14 relates to how Signature Verification is mishandled. This allows for the loading of unsigned kernel modules via the init_module syscall when certain conditions are met.

The Impact of CVE-2021-35039

Without the proper configuration (CONFIG_MODULE_SIG), verification that a kernel module is signed does not occur when loading via init_module for a module.sig_enforce=1 command-line argument. This can lead to the execution of unsigned or malicious code within the kernel, potentially compromising system integrity.

Technical Details of CVE-2021-35039

Let's delve deeper into the technical aspects of the CVE-2021-35039 vulnerability.

Vulnerability Description

The vulnerability arises due to the mishandling of Signature Verification in the kernel/module.c file. This oversight allows unsigned kernel modules to be loaded without proper signature checks.

Affected Systems and Versions

The issue impacts the Linux kernel versions before 5.12.14. Systems running these versions are vulnerable to the exploitation of this security flaw.

Exploitation Mechanism

Attackers can exploit this vulnerability by providing a module.sig_enforce=1 command-line argument when loading kernel modules via the init_module syscall, bypassing the signature verification check.

Mitigation and Prevention

Here, we will discuss the steps to mitigate and prevent the exploitation of CVE-2021-35039.

Immediate Steps to Take

Users and administrators should apply patches provided by the Linux kernel team to update their systems to version 5.12.14 or later. It is crucial to ensure that CONFIG_MODULE_SIG is properly configured to enforce proper signature verification.

Long-Term Security Practices

Incorporate secure coding practices to prevent similar vulnerabilities in the future. Regularly update and patch the kernel to address any security issues promptly.

Patching and Updates

Regularly check for security advisories from Linux kernel vendors and apply patches as soon as they are available to keep systems secure.