# CVE-2026-39324: ruby-rack-session: Rack::Session is a session management implementation for Rack

CVE-2026-39324 is fixed in ruby-rack-session on 1 platform, first by ruby-rack-session 2.1.1-0.1ubuntu0.26.04.1, released April 7, 2026. It is not reported as exploited. Patch Radar priority: Urgent.

- Web page: https://patchblox.com/security/cve/CVE-2026-39324
- Priority: Urgent
- CVSS: 9.8 (critical)
- EPSS: 0.0027
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Apr 7, 2026

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | ruby-rack-session Debian 13.5 (trixie) | 2.1.1-0.1+deb13u1 | [DEBIAN-CVE-2026-39324](https://patchblox.com/security/data/fix/linux/debian-cve-2026-39324.md) | Apr 7, 2026 |
| Linux | ruby-rack-session Debian 14 | 2.1.1-0.2 | [DEBIAN-CVE-2026-39324](https://patchblox.com/security/data/fix/linux/debian-cve-2026-39324.md) | Apr 7, 2026 |
| Linux | ruby-rack-session Ubuntu 25.10 (questing) | 2.1.1-0.1ubuntu0.1 | [ruby-rack-session 2.1.1-0.1ubuntu0.1](https://patchblox.com/security/data/fix/linux/ubuntu-questing-ruby-rack-session-2.1.1-0.1ubuntu0.1.md) | Apr 30, 2026 |
| Linux | ruby-rack-session Ubuntu 26.04.1 LTS (resolute) | 2.1.1-0.1ubuntu0.26.04.1 | [ruby-rack-session 2.1.1-0.1ubuntu0.26.04.1](https://patchblox.com/security/data/fix/linux/ubuntu-resolute-ruby-rack-session-2.1.1-0.1ubuntu0.26.04.1.md) | Apr 7, 2026 |

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Data as of 2026-11-09T01:18:40Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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