{"description":"Trending threats, MITRE ATT\u0026CK coverage, and detection metadata. Fed continuously.","feed_url":"https://feed.craftedsignal.io/tags/session/feed.json","home_page_url":"https://feed.craftedsignal.io/","items":[{"_cs_actors":[],"_cs_cpes":[],"_cs_cves":[{"id":"CVE-2026-39324"}],"_cs_exploited":false,"_cs_has_poc":false,"_cs_poc_references":[],"_cs_products":["rack-session"],"_cs_severities":["critical"],"_cs_tags":["rack","session","cookie","deserialization","vulnerability","privilege-escalation"],"_cs_type":"advisory","_cs_vendors":["Rack"],"content_html":"\u003cp\u003eThe \u003ccode\u003eRack::Session::Cookie\u003c/code\u003e gem, versions 2.0.0 to before 2.1.2, contains a critical vulnerability where decryption failures are mishandled. When configured with the \u003ccode\u003esecrets:\u003c/code\u003e option, the system should decrypt incoming session cookies. However, if decryption fails, instead of rejecting the cookie, it falls back to a default decoder. This allows an unauthenticated attacker to craft a session cookie that the application accepts as valid, even without knowing the encryption secret. This behavior bypasses intended integrity protections and exposes applications to unauthorized access by allowing manipulation of session contents. Rails applications are typically not affected as they use \u003ccode\u003eActionDispatch::Session::CookieStore\u003c/code\u003e.\u003c/p\u003e\n\u003ch2 id=\"attack-chain\"\u003eAttack Chain\u003c/h2\u003e\n\u003col\u003e\n\u003cli\u003eThe attacker identifies a Rack application using \u003ccode\u003eRack::Session::Cookie\u003c/code\u003e with the \u003ccode\u003esecrets:\u003c/code\u003e option.\u003c/li\u003e\n\u003cli\u003eThe attacker crafts a malicious session cookie payload.\u003c/li\u003e\n\u003cli\u003eThe attacker sends an HTTP request to the application with the crafted session cookie.\u003c/li\u003e\n\u003cli\u003eThe application attempts to decrypt the cookie using configured secrets, but decryption fails.\u003c/li\u003e\n\u003cli\u003eInstead of rejecting the cookie, \u003ccode\u003eRack::Session::Cookie\u003c/code\u003e falls back to a default decoder.\u003c/li\u003e\n\u003cli\u003eThe application deserializes the attacker-controlled cookie data, treating it as trusted session state.\u003c/li\u003e\n\u003cli\u003eThe attacker manipulates session contents (e.g., user ID, roles, permissions).\u003c/li\u003e\n\u003cli\u003eThe attacker gains unauthorized access or elevates privileges based on the manipulated session data.\u003c/li\u003e\n\u003c/ol\u003e\n\u003ch2 id=\"impact\"\u003eImpact\u003c/h2\u003e\n\u003cp\u003eAny Rack application using a vulnerable version of \u003ccode\u003eRack::Session::Cookie\u003c/code\u003e with the \u003ccode\u003esecrets:\u003c/code\u003e option is susceptible. Exploitation can lead to authentication bypass, privilege escalation, and potentially other risks depending on the specific application logic. An attacker can supply a crafted session cookie that is accepted as valid session data, potentially leading to unauthorized actions being performed with the privileges of a legitimate user. The number of victims depends on the popularity and exposure of vulnerable Rack applications.\u003c/p\u003e\n\u003ch2 id=\"recommendation\"\u003eRecommendation\u003c/h2\u003e\n\u003cul\u003e\n\u003cli\u003eUpgrade to \u003ccode\u003erack-session\u003c/code\u003e version 2.1.2 or later to remediate CVE-2026-39324 and ensure proper cookie decryption failure handling.\u003c/li\u003e\n\u003cli\u003eRotate session secrets after upgrading \u003ccode\u003erack-session\u003c/code\u003e to invalidate existing session cookies that may have been forged by attackers.\u003c/li\u003e\n\u003cli\u003eMonitor web server logs (category: webserver, product: linux/windows) for suspicious HTTP requests containing unusually long or malformed session cookies, indicating potential exploitation attempts.\u003c/li\u003e\n\u003cli\u003eDeploy the Sigma rule \u0026quot;Detect Suspicious Rack Session Cookie Manipulation\u0026quot; to identify potential exploitation attempts based on HTTP request patterns.\u003c/li\u003e\n\u003c/ul\u003e\n","date_modified":"2024-01-02T12:00:00Z","date_published":"2024-01-02T12:00:00Z","id":"https://feed.craftedsignal.io/briefs/2024-01-02-rack-session-cookie-deserialization/","summary":"Rack::Session::Cookie incorrectly handles decryption failures, falling back to a default decoder and allowing attackers to forge session cookies without knowing the secret, potentially leading to authentication bypass or privilege escalation in vulnerable Rack applications.","title":"Rack::Session::Cookie Vulnerability Enables Secretless Session Forgery","url":"https://feed.craftedsignal.io/briefs/2024-01-02-rack-session-cookie-deserialization/"}],"language":"en","title":"CraftedSignal Threat Feed - Session","version":"https://jsonfeed.org/version/1.1"}