CVE-2023-4809 : Exploit Details and Defense Strategies

This CVE-2023-4809 affects FreeBSD systems, specifically the packet filter (pf) module. It was discovered by Enrico Bassetti from NetSecurityLab at Sapienza University of Rome. The vulnerability was published on September 6, 2023, by FreeBSD.

Understanding CVE-2023-4809

This vulnerability in pf involves the incorrect handling of multiple IPv6 fragment headers, leading to potential bypass of firewall rules and improper packet processing.

What is CVE-2023-4809?

In pf packet processing with a 'scrub fragment reassemble' rule, a packet containing multiple IPv6 fragment headers would be reassembled and immediately processed. This means that a packet with multiple fragment extension headers would not be recognized as the correct ultimate payload. Instead, it would be interpreted as a fragmented packet, potentially allowing IPv6 fragments to bypass pf firewall rules and be forwarded or processed by the host.

The Impact of CVE-2023-4809

The impact of this vulnerability is significant as it could lead to the improper handling of network traffic, allowing malicious packets to bypass firewall protections and potentially compromise the system's security.

Technical Details of CVE-2023-4809

This section provides more detailed information about the vulnerability.

Vulnerability Description

The vulnerability arises from the mishandling of multiple IPv6 fragment headers in the packet filter module, enabling potentially malicious fragments to evade firewall rules.

Affected Systems and Versions

FreeBSD 13.2-RELEASE (less than p3)
FreeBSD 12.4-RELEASE (less than p5)

Exploitation Mechanism

By sending a crafted packet containing multiple IPv6 fragment headers, an attacker could exploit this vulnerability to bypass firewall rules and potentially launch further attacks on the system.

Mitigation and Prevention

To address CVE-2023-4809, immediate actions and long-term security practices are recommended.

Immediate Steps to Take

System administrators are advised to apply the patches provided by FreeBSD to mitigate the vulnerability. Additionally, monitoring network traffic for any suspicious activities can help detect potential exploitation attempts.

Long-Term Security Practices

Implementing network segmentation, regularly updating firewall rules, and conducting security audits can enhance the overall resilience of the system against similar vulnerabilities in the future.

Patching and Updates

Users are urged to apply the necessary patches and updates released by FreeBSD to address the vulnerability promptly and ensure the security of their systems.