CVE-2025-46727 is a high-severity vulnerability affecting the Rack Ruby web server interface, specifically its QueryParser component. Rack is widely used in Ruby web applications to handle HTTP requests and responses. The vulnerability exists in versions prior to 2.2.14, 3.0.16, and 3.1.14, where Rack::QueryParser does not impose any limits on the number of parameters parsed from query strings or application/x-www-form-urlencoded request bodies. This lack of bounds allows an attacker to craft HTTP requests containing an extremely large number of parameters, potentially hundreds of thousands or more. During parsing, Rack::QueryParser iterates over each key-value pair separated by '&' and adds them to a Hash without restriction, leading to uncontrolled resource consumption. The excessive memory allocation and CPU usage can exhaust server resources, causing denial of service (DoS) by stalling or crashing the Rack server process. This results in full service disruption until the affected worker is restarted. The vulnerability is exploitable remotely without authentication or user interaction, increasing its risk. The CVSS 3.1 score of 7.5 reflects a high severity, with network attack vector, low attack complexity, no privileges required, and no user interaction needed. Mitigations include upgrading to fixed versions 2.2.14, 3.0.16, or 3.1.14. Additional defenses involve deploying middleware to enforce maximum query string sizes or parameter counts, using reverse proxies like Nginx to limit request sizes and reject oversized queries or bodies, and limiting request body sizes at the web server or CDN level. These mitigations help prevent resource exhaustion by filtering or blocking maliciously large requests before they reach the Rack application.

For European organizations, this vulnerability poses a significant risk of denial of service attacks against web applications built on Ruby using vulnerable Rack versions. Organizations relying on Ruby on Rails or other Rack-based frameworks may experience service outages, degraded performance, or crashes due to resource exhaustion triggered by malicious HTTP requests. This can disrupt business operations, degrade customer experience, and potentially cause financial losses or reputational damage. Since the vulnerability requires no authentication or user interaction, attackers can exploit it remotely at scale, increasing the likelihood of widespread impact. Critical services such as e-commerce platforms, government portals, financial services, and healthcare applications using Rack are particularly at risk. The disruption of these services can affect data availability and operational continuity, which are essential for compliance with European regulations like GDPR that mandate service reliability and data protection. Additionally, the increased CPU and memory usage may lead to higher infrastructure costs or trigger automated scaling that could be exploited for economic denial of service.

European organizations should prioritize upgrading all Rack dependencies to versions 2.2.14, 3.0.16, or 3.1.14, which contain the official patches for this vulnerability. Where immediate upgrades are not feasible, implement middleware solutions that enforce strict limits on the maximum number of query parameters and the overall query string size to prevent excessive resource consumption during parsing. Deploy reverse proxies such as Nginx or Apache in front of Rack applications to limit the size of HTTP request bodies and query strings, rejecting requests that exceed configured thresholds. Configure web application firewalls (WAFs) to detect and block anomalous requests with unusually large numbers of parameters. Additionally, leverage CDN capabilities to filter oversized requests at the edge, reducing load on origin servers. Monitor application and server metrics for unusual spikes in CPU or memory usage that may indicate exploitation attempts. Establish incident response procedures to quickly restart affected workers or servers to restore service availability. Finally, conduct security awareness training for development teams to ensure secure coding practices and timely dependency management.