Session Management Vulnerability in Rack's Cookie Implementation
CVE-2026-39324

9.3CRITICAL

Key Information:

Vendor

Rack

Status
Rack-session
Vendor
CVE Published:
7 April 2026

Badges

👾 Exploit Exists🟡 Public PoC

What is CVE-2026-39324?

An issue has been identified in Rack::Session's cookie implementation, where decryption failures in session management are not adequately handled. When configured with secrets, if cookie decryption fails, an incorrect fallback to a default decoder occurs instead of rejecting the cookie. This flaw permits an unauthenticated attacker to submit a specially crafted session cookie that is mistakenly accepted as valid session data, circumventing the need for knowledge of any configured secret. This vulnerability can lead to unauthorized access by allowing manipulation of session content.

Affected Version(s)

rack-session >= 2.0.0, < 2.1.2

Exploit Proof of Concept (PoC)

PoC code is written by security researchers to demonstrate the vulnerability can be exploited. PoC code is also a key component for weaponization which could lead to ransomware.

CVE-2026-39324
Created by sm1ee

References

https://github.com/rack/rack-session/security/advisories/...
x_refsource_CONFIRM

CVSS V4

Score:
9.3
Severity:
CRITICAL
Confidentiality:
High
Integrity:
High
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
None
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • 🟡

    Public PoC available

  • 👾

    Exploit known to exist

  • Vulnerability published

  • Vulnerability Reserved

.