Plateforme
ruby
Composant
rack-session
Corrigé dans
2.0.1
2.1.2
CVE-2026-39324 describes an insecure deserialization vulnerability within the Rack::Session::Cookie component of the rack-session Ruby gem. This flaw allows an attacker to craft malicious session cookies, effectively bypassing authentication mechanisms and potentially gaining unauthorized access to sensitive data and functionality. The vulnerability affects versions of rack-session up to and including 2.1.1, and a fix is available in version 2.1.2.
The core of the vulnerability lies in how Rack::Session::Cookie handles decryption failures. When configured with secrets:, the component is intended to decrypt session cookies using a provided secret. However, if decryption fails, the implementation incorrectly falls back to a default decoder instead of rejecting the cookie outright. This bypass allows an attacker to supply a crafted session cookie that is accepted as valid, even without knowing the correct secret. Successful exploitation could lead to complete account takeover, data breaches, and potentially even remote code execution depending on the application's session handling logic. This is particularly concerning for applications relying on rack-session for managing user sessions.
CVE-2026-39324 was publicly disclosed on 2026-04-07. The vulnerability's severity is rated as CRITICAL (CVSS 9.5). There are currently no known public exploits or active campaigns targeting this vulnerability, but the ease of exploitation makes it a high-priority concern. It is not currently listed on the CISA KEV catalog. Public proof-of-concept code is likely to emerge given the vulnerability's nature.
Applications built with Ruby on Rails or other Ruby frameworks that utilize the rack-session gem for session management are at risk. This includes web applications deployed on shared hosting environments where the underlying Ruby environment may be managed by the hosting provider. Legacy applications using older versions of rack-session are particularly vulnerable.
• ruby / server:
grep -r 'Rack::Session::Cookie' /path/to/your/app/config.ru
grep -r 'secrets:' /path/to/your/app/config.ru• ruby / supply-chain:
Check your Gemfile for rack-session versions less than 2.1.2.
gem list rack-session
• generic web:
Inspect session cookie values for unusual or unexpected data. Monitor for unusual session activity.
disclosure
Statut de l'Exploit
EPSS
0.04% (percentile 12%)
CISA SSVC
The primary mitigation for CVE-2026-39324 is to immediately upgrade to rack-session version 2.1.2 or later. If upgrading is not immediately feasible due to compatibility issues or breaking changes, consider implementing a temporary workaround by carefully validating session cookies on the application level. This could involve checking the integrity of the cookie contents or implementing stricter authentication checks. Additionally, consider using a Web Application Firewall (WAF) with rules to detect and block suspicious session cookie patterns. After upgrading, verify the fix by attempting to forge a session cookie and confirming that it is rejected.
Actualice la biblioteca Rack::Session a la versión 2.1.2 o superior para mitigar la vulnerabilidad. Esta actualización corrige el manejo incorrecto de errores de descifrado de cookies, evitando la posibilidad de falsificación de sesiones sin secretos.
Analyses de vulnérabilités et alertes critiques directement dans votre boîte mail.
CVE-2026-39324 is a critical vulnerability in Rack::Session versions up to 2.1.1 that allows attackers to forge session cookies, bypassing authentication.
If you are using Rack::Session version 2.1.1 or earlier, you are affected by this vulnerability. Check your Gemfile to confirm.
Upgrade to Rack::Session version 2.1.2 or later to resolve the insecure deserialization vulnerability.
Currently, there are no confirmed reports of active exploitation, but the ease of exploitation makes it a high-priority concern.
Refer to the official Rack::Session project documentation and related security advisories for more information.
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