CVE-2023-39189 : Exploit Details and Defense Strategies

A flaw was discovered in the Netfilter subsystem in the Linux kernel. This vulnerability, assigned CVE-2023-39189, allows a local privileged attacker to trigger an out-of-bounds read, potentially leading to a crash or information disclosure. Here is a detailed overview of the CVE-2023-39189 vulnerability.

Understanding CVE-2023-39189

CVE-2023-39189 is a moderate-severity vulnerability affecting the Netfilter subsystem in the Linux kernel. It was reported to Red Hat on July 25, 2023, and made public on August 30, 2023.

What is CVE-2023-39189?

A flaw was found in the Netfilter subsystem in the Linux kernel. The nfnl_osf_add_callback function did not validate the user mode-controlled opt_num field. This flaw allows a local privileged (CAP_NET_ADMIN) attacker to trigger an out-of-bounds read, leading to a crash or information disclosure.

The Impact of CVE-2023-39189

The vulnerability has a base score of 5.1, indicating a medium severity level. It can be exploited by a local attacker with high privileges, potentially resulting in a denial of service or sensitive information exposure.

Technical Details of CVE-2023-39189

This section provides more insights into the vulnerability, including its description, affected systems, and exploitation mechanism.

Vulnerability Description

The nfnl_osf_add_callback function in the Linux kernel's Netfilter subsystem lacks proper validation, allowing a local attacker to trigger an out-of-bounds read, leading to a system crash or disclosure of sensitive information.

Affected Systems and Versions

Kernel version 6.6-rc1 is unaffected.
Red Hat Enterprise Linux 6, 7, 8, 9 are affected by this vulnerability.
Fedora systems are also affected.

Exploitation Mechanism

The vulnerability can be exploited by a local privileged attacker with CAP_NET_ADMIN permissions to manipulate the opt_num field, triggering an out-of-bounds read.

Mitigation and Prevention

To address CVE-2023-39189, immediate steps should be taken to secure affected systems and prevent potential exploitation.

Immediate Steps to Take

Mitigate the vulnerability by blacklisting the affected Passive OS Fingerprinting match module (

xt_osf

) from being loaded. Refer to Red Hat's advisory for instructions on how to blacklist a kernel module.

Long-Term Security Practices

Ensure regular security updates and patches are applied to the affected systems to mitigate the risk of exploitation and enhance overall security posture.

Patching and Updates

Keep abreast of security updates and patches released by vendors like Red Hat and Fedora to address CVE-2023-39189 and other security vulnerabilities.