CVE-2025-46336 is a medium-severity vulnerability affecting the Rack::Session component of the Rack web application framework, specifically versions from 2.0.0 up to but not including 2.1.1. Rack::Session is responsible for managing user sessions in Rack-based Ruby web applications. The vulnerability arises in the Rack::Session::Pool middleware, which stores session data in memory. The issue is a race condition (CWE-362) related to improper synchronization when handling concurrent requests sharing the same session resource. An attacker who has already obtained a valid session cookie—which itself is a significant prerequisite—can exploit this flaw by triggering a long-running request within the same session concurrently with a legitimate user logging out. Due to the race condition, the session state may be restored or retained improperly, allowing the attacker to maintain illicit access even after the user has attempted to terminate their session. This undermines session invalidation and logout mechanisms, potentially enabling session fixation or session hijacking persistence. The vulnerability does not require user interaction but does require the attacker to have some level of privilege (low) and network access. The CVSS 3.1 base score is 4.2, reflecting low confidentiality and integrity impacts, no availability impact, high attack complexity, and limited privileges required. No known exploits are currently reported in the wild. The issue has been addressed in Rack::Session version 2.1.1, where proper synchronization mechanisms have been implemented to prevent concurrent session restoration after logout.

For European organizations, this vulnerability poses a risk primarily to web applications built on the Ruby Rack framework that use the Rack::Session::Pool middleware within the affected versions. The impact is the potential for attackers to maintain unauthorized access to user sessions even after logout, which could lead to unauthorized data access, privilege escalation within the application, and potential data leakage. Although the vulnerability requires the attacker to have obtained a session cookie, which may involve other security weaknesses, the persistence of session access after logout undermines user trust and session management security. This could affect sectors with sensitive user data such as finance, healthcare, and e-commerce. The medium severity rating suggests that while the vulnerability is not trivially exploitable, it can be leveraged in targeted attacks, especially in environments where session cookies are not well protected or where long-running requests are common. Additionally, regulatory frameworks in Europe such as GDPR emphasize protecting user data and session integrity, so exploitation could lead to compliance issues and reputational damage.

European organizations should immediately audit their use of the Rack::Session middleware and identify any applications running versions >= 2.0.0 and < 2.1.1. The primary mitigation is to upgrade to Rack::Session version 2.1.1 or later, where the race condition has been fixed. If immediate upgrading is not feasible, organizations should consider implementing additional session management controls such as: enforcing shorter session lifetimes, invalidating sessions server-side upon logout explicitly, and monitoring for abnormal concurrent session activity. Application-level mitigations include avoiding long-running requests that share session state or isolating session storage to prevent concurrent access conflicts. Additionally, organizations should ensure secure handling of session cookies by using secure, HttpOnly, and SameSite flags to reduce the risk of session cookie theft. Implementing multi-factor authentication can also reduce the impact of session compromise. Regular security testing and code reviews focusing on concurrency and session management are recommended to prevent similar issues.