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CVE-2026-39324

Rack Rack-session insecure deserialization

9.8 CRITICALEPSS 0.27%
  1. Published7 Apr 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.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Affected products

Rack Rack-session≥ 2.0.0 < 2.1.2

Remediation

Fixed in
Rack Rack-session≥ 2.1.2

References

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Frequently asked

Is CVE-2026-39324 being actively exploited?

CVE-2026-39324 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.27%.

How severe is CVE-2026-39324?

CVE-2026-39324 has a CVSS 3.1 base score of 9.8, rated critical. EPSS estimates a 0.27% probability of exploitation.

Which products are affected by CVE-2026-39324?

Affected products include Rack Rack-session.

How do I fix CVE-2026-39324?

Upgrade affected software to a fixed version, for example Rack Rack-session 2.1.2 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-39324 against the real software inventory on every managed device, every day. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.