Rack::Session::Cookie secrets: decrypt failure fallback enables secretless session forgery and Marshal deserialization
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Attack requirements
- None
- Impact type
- Security bypass, Code execution
- Confidentiality · integrity · availability
- High · High · High
- Fix status
- Fixed
Attack profile from CVSS 4.0 · CNA. Fix status from CNA and GitHub. Impact type from CWE-287 and CWE-502.
Summary
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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- Yes
- Technical impact
- Total
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| rack | rack-session | 2.0.0 to before 2.1.2 | 2.1.2 | Patch available | CNA |
| — | rack-session (RubyGems) | 2.0.0 to before 2.1.2 | 2.1.2 | Patch available | GHSA-33qg-7wpp-89cq |
- rack-session Vendorrack Affected 2.0.0 to before 2.1.2 Fixed in 2.1.2 Patch available CNA
- rack-session (RubyGems) Vendor— Affected 2.0.0 to before 2.1.2 Fixed in 2.1.2 Patch available GHSA-33qg-7wpp-89cq
Remediation
- Fix · CNA rack-session (rack) Fixed in 2.1.2
- Fix · GHSA-33qg-7wpp-89cq rack-session (RubyGems) Fixed in 2.1.2 Advisory →
Vendor assessments
Red Hat
Red Hat rating: Critical. Red Hat's page for this CVE →
Not affected: 1 product
- Red Hat 3scale API Management Platform 2
Timeline
- 2026-10-02 Threatist record created from CVE-2026-39324
- 2026-10-03 Alias added: GHSA-33qg-7wpp-89cq
- 2026-10-13 Affected versions changed · Red Hat
References
Sources
- CVE-2026-39324 · CVE Program
- CVE-2026-39324 · NVD
- FIRST EPSS
- GHSA-33qg-7wpp-89cq · GitHub Advisory Database · CC BY 4.0
- CVE-2026-39324 · Red Hat security data · CC BY 4.0
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