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Description

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.

PUBLISHED Reserved 2026-04-06 | Published 2026-04-07 | Updated 2026-04-08 | Assigner GitHub_M




CRITICAL: 9.3CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Problem types

CWE-287: Improper Authentication

CWE-345: Insufficient Verification of Data Authenticity

CWE-502: Deserialization of Untrusted Data

CWE-565: Reliance on Cookies without Validation and Integrity Checking

Product status

>= 2.0.0, < 2.1.2
affected

References

github.com/...ession/security/advisories/GHSA-33qg-7wpp-89cq

cve.org (CVE-2026-39324)

nvd.nist.gov (CVE-2026-39324)

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