CVE-2023-46589 is a vulnerability classified under CWE-444 (Inconsistent Interpretation of HTTP Requests), commonly known as HTTP request smuggling, affecting multiple versions of Apache Tomcat from 8.5.0 to 11.0.0-M10. The root cause lies in Tomcat's improper input validation and parsing of HTTP trailer headers. Specifically, when a trailer header exceeds the configured header size limit, Tomcat incorrectly processes what should be a single HTTP request as multiple distinct requests. This parsing inconsistency can be exploited by an attacker positioned between a client and a reverse proxy or load balancer to smuggle crafted HTTP requests. Such smuggled requests can bypass security controls, poison web caches, or manipulate backend application logic. The vulnerability does not require authentication or user interaction, making it exploitable remotely over the network. The flaw affects Tomcat deployments behind reverse proxies, a common architecture in enterprise environments. Although no active exploits have been reported, the potential for impactful attacks exists due to the widespread use of Tomcat in web servers and application servers globally. The Apache Software Foundation has addressed the issue in versions 8.5.96, 9.0.83, 10.1.16, and 11.0.0-M11 and later. Organizations running affected versions should upgrade promptly to mitigate risk. The CVSS v3.1 base score of 7.5 reflects a high severity due to the vulnerability's network attack vector, lack of required privileges, and significant impact on request integrity without affecting confidentiality or availability.

For European organizations, the impact of CVE-2023-46589 can be significant, particularly for those relying on Apache Tomcat for hosting web applications, APIs, or internal services behind reverse proxies. Exploitation could allow attackers to bypass security controls such as web application firewalls, authentication mechanisms, or input validation filters by smuggling malicious requests. This can lead to unauthorized actions, data manipulation, or cache poisoning, undermining the integrity of web services. Critical sectors such as finance, healthcare, government, and telecommunications, which often deploy Tomcat in their infrastructure, may face increased risk of targeted attacks aiming to disrupt services or manipulate data. The vulnerability's network-based exploitation without authentication means attackers can attempt exploitation remotely, increasing the attack surface. Additionally, compromised request integrity can facilitate further attacks like session hijacking or privilege escalation. While no confidentiality breach is directly indicated, the indirect consequences of request smuggling can lead to sensitive information exposure or unauthorized access. The absence of known exploits in the wild provides a window for proactive mitigation, but the widespread use of Tomcat in Europe necessitates urgent patching to prevent potential exploitation.

To mitigate CVE-2023-46589 effectively, European organizations should: 1) Immediately upgrade Apache Tomcat to the fixed versions: 8.5.96 or later, 9.0.83 or later, 10.1.16 or later, or 11.0.0-M11 or later. 2) Review and harden reverse proxy and load balancer configurations to detect and reject malformed or oversized HTTP headers, including trailer headers, to prevent request smuggling attempts. 3) Implement strict input validation and size limits on HTTP headers at the proxy level to complement Tomcat's protections. 4) Monitor web server and proxy logs for anomalies indicative of request smuggling, such as unexpected request splitting or unusual header patterns. 5) Conduct penetration testing and security assessments focusing on HTTP request smuggling vectors to identify residual risks. 6) Employ Web Application Firewalls (WAFs) with updated signatures capable of detecting HTTP request smuggling attacks. 7) Educate development and operations teams about the risks of HTTP request smuggling and the importance of timely patching and secure configuration. 8) For legacy or EOL Tomcat versions that cannot be immediately upgraded, consider isolating affected servers behind additional security layers or disabling HTTP trailer header support if feasible. These targeted actions go beyond generic patching advice and address the specific exploitation method and deployment context of this vulnerability.