CVE-2023-4236 Explained : Impact and Mitigation

This CVE-2023-4236 article provides detailed information about a vulnerability affecting BIND 9 that can lead to unexpected termination of the

named

service under high DNS-over-TLS query loads.

Understanding CVE-2023-4236

The flaw in the networking code handling DNS-over-TLS queries can trigger an assertion failure in

named

, causing unexpected termination. This vulnerability affects certain versions of BIND 9 due to incorrect reuse of internal data structures during significant DNS-over-TLS query loads.

What is CVE-2023-4236?

CVE-2023-4236 is a vulnerability in BIND 9 that can result in the unexpected termination of the

named

service under high DNS-over-TLS query loads. This flaw impacts specific versions of BIND 9 and poses a risk to systems using DNS-over-TLS functionality.

The Impact of CVE-2023-4236

Systems running vulnerable versions of BIND 9 may experience unexpected termination of the

named

service when subjected to significant DNS-over-TLS query loads. Notably, this flaw does not affect DNS-over-HTTPS functionality, as it utilizes a different TLS implementation.

Technical Details of CVE-2023-4236

The vulnerability description, affected systems and versions, and the exploitation mechanism are crucial aspects to consider for understanding and addressing CVE-2023-4236.

Vulnerability Description

The flaw in the networking code handling DNS-over-TLS queries may lead to unexpected termination of the

named

service due to an assertion failure. This occurs when internal data structures are incorrectly reused under significant DNS-over-TLS query loads.

Affected Systems and Versions

BIND 9 versions 9.18.0 through 9.18.18 and 9.18.11-S1 through 9.18.18-S1 are affected by this vulnerability. Systems running these versions are at risk of experiencing the unexpected termination of the

named

service under high DNS-over-TLS query loads.

Exploitation Mechanism

Disabling listening for DNS-over-TLS connections is recommended as a workaround to prevent the affected code paths from being taken, rendering exploitation impossible. However, if DNS-over-TLS support is necessary, there is no direct workaround available.

Mitigation and Prevention

Understanding the immediate steps to take, incorporating long-term security practices, and applying patching and updates are essential to mitigate the risks associated with CVE-2023-4236.

Immediate Steps to Take

To mitigate the vulnerability, it is recommended to upgrade to the patched release most closely related to the current BIND 9 version – 9.18.19 or 9.18.19-S1. Additionally, consider disabling listening for DNS-over-TLS connections if feasible.

Long-Term Security Practices

Implementing secure configuration practices, monitoring for security advisories, and staying informed about vulnerabilities in BIND 9 are crucial for long-term security resilience against potential threats.

Patching and Updates

Regularly applying patches and updates provided by the vendor, such as upgrading to the latest secure release of BIND 9, is essential to address known vulnerabilities and enhance the security posture of the affected systems.

Credit: ISC would like to thank Robert Story from the USC/ISI DNS root server operations team for discovering and reporting this vulnerability.

References:

CVE-2023-4236 Advisory by ISC
Openwall Mailing List - OSS Security
Debian Security Advisory DSA-5504
Fedora Project - Package Announce
Fedora Project - Package Announce
NetApp Security Advisory NTAP-20231013-0004
Fedora Project - Package Announce