CVE-2023-46589 is a high-severity vulnerability affecting multiple versions of Apache Tomcat, a widely used open-source Java servlet container and web server. The vulnerability is classified under CWE-444, which relates to inconsistent interpretation of HTTP requests, commonly known as HTTP Request Smuggling. Specifically, the issue arises from improper input validation in the way Apache Tomcat parses HTTP trailer headers. In affected versions (from 8.5.0 through 8.5.95, 9.0.0-M1 through 9.0.82, 10.1.0-M1 through 10.1.15, and 11.0.0-M1 through 11.0.0-M10), Tomcat does not correctly handle trailer headers that exceed the configured header size limit. This can cause Tomcat to misinterpret a single HTTP request as multiple separate requests. When Tomcat is deployed behind a reverse proxy, this inconsistent parsing can be exploited to perform HTTP Request Smuggling attacks. Such attacks allow an attacker to bypass security controls, poison web caches, perform cross-site scripting, or gain unauthorized access by manipulating how requests are processed between front-end proxies and back-end servers. The vulnerability does not require authentication or user interaction and can be exploited remotely over the network. The Apache Software Foundation has addressed this issue in versions 8.5.96 and later, 9.0.83 and later, 10.1.16 and later, and 11.0.0-M11 and later. No known exploits are currently reported in the wild, but the nature of the vulnerability and its CVSS score of 7.5 (high) indicate a significant risk if left unpatched.

For European organizations, the impact of CVE-2023-46589 can be substantial, especially for those relying on Apache Tomcat as part of their web infrastructure. HTTP Request Smuggling can lead to unauthorized access, session hijacking, cache poisoning, and bypassing of security controls such as web application firewalls and authentication mechanisms. This can compromise the integrity of web applications, potentially leading to data breaches or service disruptions. Given the widespread use of Tomcat in enterprise applications, government portals, and critical infrastructure, exploitation could affect confidentiality and integrity of sensitive data. Additionally, organizations operating behind reverse proxies or load balancers are particularly vulnerable. The attack could also facilitate lateral movement within networks or enable further exploitation by attackers. The absence of known exploits in the wild currently provides a window for proactive mitigation, but the high severity and ease of remote exploitation necessitate urgent attention.

European organizations should prioritize upgrading 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. Beyond patching, organizations should audit their reverse proxy and load balancer configurations to ensure they correctly handle HTTP headers and do not allow ambiguous request parsing. Implementing strict input validation and size limits on HTTP headers at the proxy level can reduce risk. Monitoring HTTP traffic for anomalies indicative of request smuggling attempts is advisable, using advanced web application firewalls capable of detecting such attacks. Network segmentation and limiting exposure of Tomcat servers to only necessary clients can reduce attack surface. Additionally, organizations should review and update incident response plans to include detection and mitigation strategies for HTTP Request Smuggling. Regular security assessments and penetration testing focusing on HTTP protocol handling can help identify residual risks.