CVE-2025-27219: 
Ruby vulnerability analysis and mitigation

The CGI gem for Ruby, prior to version 0.4.2, contains a Denial of Service (DoS) vulnerability identified as CVE-2025-27219. The vulnerability exists in the CGI::Cookie.parse method of the CGI library, which fails to implement limits on the length of raw cookie values during processing. This vulnerability was discovered on February 26, 2025, affecting multiple versions of the CGI gem including versions <= 0.3.5, 0.3.6, 0.4.0, and 0.4.1 (Ruby Advisory DB, NVD).

The vulnerability stems from the CGI::Cookie.parse method taking super-linear time to parse cookie strings in certain cases. The method's implementation lacks proper validation for the length of raw cookie values it processes, which can lead to excessive resource consumption. The vulnerability has been assigned a CVSS v3.1 base score of 7.5 (HIGH) by NIST and 5.8 (MEDIUM) by MITRE, with the vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. The vulnerability is classified under CWE-770 (Allocation of Resources Without Limits or Throttling) (NVD).

When exploited, this vulnerability can lead to Denial of Service conditions through excessive resource consumption. By feeding maliciously crafted cookie strings into the affected method, attackers can cause the application to consume excessive resources, potentially impacting system availability (Ruby Advisory DB).

The vulnerability can be exploited remotely by sending specially crafted cookie values to applications using the affected versions of the CGI gem. No authentication is required to exploit this vulnerability, making it particularly concerning for public-facing applications (NVD).

Users are recommended to upgrade to CGI gem version 0.3.5.1, 0.3.7, 0.4.2 or later, which contain patches for this vulnerability. The fix has been implemented to address the super-linear time complexity issue in cookie string parsing (Ruby Advisory DB).