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CVE-2026-39324

Critical Vulnerability: CVE-2026-39324 — rack — rack-session

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

Wednesday, April 15, 2026rackVulnios Threat Intelligence
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Executive 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

CVE-2026-39324 is rated CRITICAL severity, requiring immediate attention from security teams.

CVSS Base Score: 9.8/10

EPSS (Exploit Prediction): 0.0% probability of exploitation in the next 30 days.

Affected Technologies

Vendors: rack

Products: rack-session

🛡️What Defenders Should Check

  • Check if you are affected — Review your asset inventory for products listed in CVE-2026-39324.
  • Apply available patches — Visit vendor advisories for the latest security updates.
  • Monitor for exploitation — Check your SIEM/IDS logs for related indicators.

    • Use Vulnios to continuously monitor your exposure to CVE-2026-39324 and similar vulnerabilities.

    References & Sources

  • https://github.com/rack/rack-session/security/advisories/GHSA-33qg-7wpp-89cq

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    Affected Products

    rack-session

    Sources

    critical

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