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katalyst-koi: Session cookies can be replayed after user logout

High severity GitHub Reviewed Published May 1, 2026 in katalyst/koi • Updated May 14, 2026

Package

bundler katalyst-koi (RubyGems)

Affected versions

< 4.20.0
>= 5.0.0, < 5.6.0

Patched versions

4.20.0
5.6.0

Description

Impact

Admin session cookies were not invalidated when an admin user logged out. An attacker with access to a valid admin session cookie could continue to access admin functionality after logout, until the cookie expired or session secrets were rotated.

This affects applications using Koi admin authentication where an admin session cookie may have been exposed, cached, intercepted, or otherwise retained after logout.

Patches

The issue has been patched by recording admin logout time and rejecting any admin session cookie created before the user’s most recent logout.

Users should upgrade to the patched Koi releases once available.

Workarounds

Katalyst Koi recommends upgrading to the latest available version, or back porting the changes released in 5.6.0/4.20.0

Resources

This is an application of https://guides.rubyonrails.org/v5.2.0/security.html#replay-attacks-for-cookiestore-sessions

References

@sfnelson sfnelson published to katalyst/koi May 1, 2026
Published to the GitHub Advisory Database May 7, 2026
Reviewed May 7, 2026
Published by the National Vulnerability Database May 14, 2026
Last updated May 14, 2026

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

EPSS score

Exploit Prediction Scoring System (EPSS)

This score estimates the probability of this vulnerability being exploited within the next 30 days. Data provided by FIRST.
(9th percentile)

Weaknesses

Insufficient Session Expiration

According to WASC, Insufficient Session Expiration is when a web site permits an attacker to reuse old session credentials or session IDs for authorization. Learn more on MITRE.

CVE ID

CVE-2026-44511

GHSA ID

GHSA-4cx3-3c38-j9vv

Source code

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