EUVD-2026-19820
GHSA-33qg-7wpp-89cq
CVSS Vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Lifecycle Timeline
4Description
Rack::Session is a session management implementation for Rack. From 2.0.0 to before 2.1.2, Rack::Session::Cookie incorrectly handles decryption failures when configured with secrets:. If cookie decryption fails, the implementation falls back to a default decoder instead of rejecting the cookie. This allows an unauthenticated attacker to supply a crafted session cookie that is accepted as valid session data without knowledge of any configured secret. Because this mechanism is used to load session state, an attacker can manipulate session contents and potentially gain unauthorized access. This vulnerability is fixed in 2.1.2.
Analysis
Session authentication bypass in Rack::Session::Cookie 2.0.0 through 2.1.1 allows unauthenticated remote attackers to forge valid session cookies and gain unauthorized access. When configured with secrets, the implementation incorrectly falls back to a default decoder on decryption failures rather than rejecting malformed cookies, enabling attackers to manipulate session state without any secret knowledge. …
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Remediation
Within 24 hours: Inventory all applications using Rack::Session::Cookie 2.0.0-2.1.1 and assess exposure to untrusted networks. Within 7 days: Implement immediate compensating controls (see below) and prepare emergency communication plan. …
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External POC / Exploit Code
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