Dnsmasq is a widely used lightweight DNS forwarder and DHCP server deployed in many network environments, including enterprise and ISP infrastructures. CVE-2023-28450 identifies a vulnerability in Dnsmasq versions prior to 2.90 related to the handling of the Extension Mechanisms for DNS (EDNS0) UDP packet size. The default maximum EDNS0 UDP packet size was set to 4096 bytes, which exceeds the recommended maximum of 1232 bytes established during DNS Flag Day 2020 to improve DNS reliability and reduce fragmentation issues. Oversized UDP packets can lead to fragmentation or packet loss, causing DNS queries to fail or time out, resulting in denial of service conditions. This vulnerability does not compromise the confidentiality or integrity of DNS data but impacts availability by disrupting DNS resolution. The CVSS v3.1 score of 7.5 reflects a high-severity rating due to the network attack vector, no required privileges or user interaction, and the potential to cause service outages. While no known exploits have been reported, the vulnerability is straightforward to exploit remotely by sending DNS queries that trigger oversized UDP responses. This can degrade or interrupt DNS services, which are critical for network operations. The vulnerability affects all deployments using vulnerable Dnsmasq versions with default configurations. Remediation requires upgrading to Dnsmasq 2.90 or later, which corrects the default EDNS0 UDP packet size to 1232 bytes, aligning with DNS Flag Day recommendations. Network administrators should also review DNS traffic patterns and consider implementing rate limiting or filtering to mitigate potential abuse. Given the fundamental role of DNS in internet and intranet communications, this vulnerability poses a significant risk to service availability.

For European organizations, this vulnerability can lead to DNS service disruptions, impacting internal and external network communications. DNS outages can cause widespread application failures, loss of internet connectivity, and degraded user experience. Critical sectors such as finance, healthcare, telecommunications, and government services that rely heavily on stable DNS infrastructure could face operational interruptions. The disruption of DNS resolution may also affect cloud services and remote work capabilities, which are prevalent in Europe. Since the vulnerability can be exploited remotely without authentication, attackers could launch denial of service attacks against vulnerable DNS servers, potentially amplifying the impact. The availability impact could cascade into broader network outages, affecting business continuity and causing financial and reputational damage. European organizations with complex network environments using Dnsmasq as part of their DNS infrastructure are particularly at risk. Additionally, the vulnerability could be leveraged in multi-stage attacks where DNS disruption is used as a diversion or to degrade defenses.

1. Upgrade all Dnsmasq instances to version 2.90 or later, which corrects the default EDNS0 UDP packet size setting to 1232 bytes. 2. Audit network devices and servers to identify any running vulnerable Dnsmasq versions and prioritize patching. 3. Configure DNS servers and firewalls to monitor and limit oversized UDP DNS packets, applying rate limiting to mitigate potential abuse. 4. Implement DNS response size controls and consider fallback to TCP for large DNS responses to avoid fragmentation issues. 5. Regularly monitor DNS traffic for anomalies that may indicate exploitation attempts or denial of service activities. 6. Educate network and security teams about the vulnerability and ensure incident response plans include DNS service disruption scenarios. 7. For critical infrastructure, consider deploying redundant DNS servers with patched software to ensure high availability. 8. Engage with upstream DNS providers and ISPs to ensure they are also protected against this vulnerability to reduce exposure.