CVE-2022-42252 is a high-severity vulnerability affecting multiple versions of Apache Tomcat, specifically versions 8.5.0 through 8.5.82, 9.0.0-M1 through 9.0.67, 10.0.0-M1 through 10.0.26, and 10.1.0-M1 through 10.1.0. The vulnerability arises from an inconsistent interpretation of HTTP requests, classified under CWE-444 (Inconsistent Interpretation of HTTP Requests, also known as HTTP Request/Response Smuggling). The root cause is linked to the handling of invalid HTTP headers, particularly the Content-Length header. In affected Tomcat versions, when configured with the rejectIllegalHeader setting set to false (which is the default for the 8.5.x branch), Tomcat does not reject requests containing invalid Content-Length headers. This behavior can be exploited when Tomcat is deployed behind a reverse proxy that also fails to reject such malformed requests. An attacker can craft specially formed HTTP requests that exploit this discrepancy between the proxy and Tomcat’s parsing logic, enabling HTTP request smuggling attacks. These attacks allow an adversary to bypass security controls, poison web caches, perform cross-user attacks, or interfere with the integrity of HTTP requests and responses. The vulnerability does not require authentication or user interaction and can be exploited remotely over the network. The CVSS v3.1 base score is 7.5 (high), reflecting the network attack vector, low attack complexity, no privileges required, no user interaction, unchanged scope, no confidentiality impact, but high integrity impact and no availability impact. No known exploits have been reported in the wild as of the publication date. However, the potential for serious integrity violations in web applications relying on vulnerable Tomcat instances is significant, especially in complex deployment environments involving reverse proxies and load balancers.

For European organizations, the impact of CVE-2022-42252 can be substantial, particularly for enterprises and public sector entities that rely on Apache Tomcat as a core component of their web infrastructure. The vulnerability enables attackers to smuggle HTTP requests, potentially bypassing security controls such as web application firewalls (WAFs), authentication mechanisms, and input validation filters. This can lead to unauthorized actions, session hijacking, cache poisoning, or injection of malicious payloads into HTTP streams. Given that many European organizations deploy Tomcat behind reverse proxies (e.g., Apache HTTP Server, NGINX, or commercial load balancers), the risk is amplified if these proxies do not properly validate HTTP headers. The integrity of web applications and APIs could be compromised, leading to data manipulation or unauthorized operations without direct data disclosure. While confidentiality impact is rated none, the ability to alter request processing can indirectly facilitate further attacks that may lead to data breaches or service disruptions. The vulnerability is particularly critical for sectors with stringent data integrity requirements such as finance, healthcare, government, and critical infrastructure. Additionally, the complexity of modern European IT environments, often involving multi-tiered proxy architectures, increases the likelihood of misconfigurations that could be exploited.

To mitigate CVE-2022-42252 effectively, European organizations should take the following specific actions: 1) Upgrade Apache Tomcat to a fixed version beyond the affected ranges as soon as possible. If immediate upgrade is not feasible, consider backporting patches or applying vendor-provided fixes. 2) Review and modify the rejectIllegalHeader configuration setting in Tomcat. For the 8.5.x branch, explicitly set rejectIllegalHeader to true to ensure that invalid HTTP headers are rejected, preventing the smuggling vector. 3) Audit and harden reverse proxy and load balancer configurations to ensure they properly validate and reject malformed HTTP headers, especially Content-Length and Transfer-Encoding headers. 4) Implement strict HTTP header validation and normalization at the proxy layer to prevent discrepancies in request parsing between the proxy and Tomcat. 5) Conduct thorough penetration testing and security assessments focusing on HTTP request smuggling scenarios to identify and remediate potential exploitation paths. 6) Monitor web server and proxy logs for anomalous or malformed HTTP requests that could indicate attempted exploitation. 7) Educate DevOps and security teams about the risks of HTTP request smuggling and the importance of consistent HTTP parsing across infrastructure components. These measures, combined with timely patching, will significantly reduce the risk posed by this vulnerability.