CVE-2025-27219 is a resource exhaustion vulnerability classified under CWE-770 (Allocation of Resources Without Limits or Throttling) found in the Ruby CGI gem prior to version 0.4.2. The flaw resides in the CGI::Cookie.parse method, which processes HTTP cookie headers without imposing any constraints on the length of the raw cookie value. An attacker can exploit this by sending an HTTP request with an excessively large cookie, causing the method to allocate and process large amounts of memory and CPU resources. This unchecked resource consumption can degrade server performance or cause the application to crash, resulting in a Denial of Service (DoS) condition. The vulnerability is remotely exploitable without requiring authentication or user interaction, increasing its risk profile. The CVSS v3.1 score is 5.8 (medium severity), reflecting the network attack vector, low attack complexity, no privileges required, and no user interaction, but limited to availability impact only. No patches were available at the time of disclosure, so mitigation relies on monitoring and limiting request sizes at the application or web server level. The vulnerability affects Ruby CGI gem versions 0, 0.3.6, and 0.4.0, which are used in web applications that handle HTTP cookies via Ruby’s CGI library.

For European organizations, this vulnerability poses a risk of service disruption through Denial of Service attacks targeting web applications that utilize the vulnerable Ruby CGI gem versions. The impact is primarily on availability, potentially causing downtime or degraded performance of critical web services. This can affect customer-facing applications, internal portals, or APIs relying on Ruby CGI for HTTP request processing. Organizations in sectors such as finance, government, healthcare, and e-commerce, which often deploy Ruby-based web applications, may experience operational interruptions and reputational damage if exploited. The lack of confidentiality or integrity impact limits data breach risks, but service outages can have cascading effects on business continuity and compliance with service-level agreements (SLAs). Given the remote exploitability and no authentication requirement, attackers can launch DoS attacks from anywhere, increasing the threat surface for European entities with internet-facing Ruby CGI applications.

To mitigate CVE-2025-27219, organizations should upgrade the Ruby CGI gem to version 0.4.2 or later as soon as a patch is released. Until then, implement strict limits on HTTP request header sizes, particularly cookie header lengths, at the web server or application firewall level to prevent processing of excessively large cookies. Employ rate limiting and anomaly detection to identify and block suspicious requests with unusually large cookie values. Review and harden web application configurations to reject malformed or oversized headers. Additionally, monitor application logs for signs of resource exhaustion or abnormal request patterns indicative of attempted exploitation. Conduct security testing to verify that cookie parsing does not lead to resource overconsumption. Finally, maintain an inventory of Ruby CGI gem versions in use across the organization to prioritize patching and risk management efforts.