Cyber Resilience

CVE-2026-21896

Access Control in Getkirby Kirby 5.0.0 – 5.2.2

Access Control
Published
08 January 2026
Modified
02 February 2026
Patch / advisory
View advisory
CVSS Score v4 5.8
Click a component to see what it means
Raw vectorCVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:A/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS Score 0.0019 9th percentile
Risk Priority 35 floored blend · peak EPSS

Summary

CVE-2026-21896 is a medium-severity Incorrect Authorization (CWE-863) vulnerability in Getkirby Kirby. Its CVSS base score is 5.8 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 9th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to AC-3 (Access Enforcement) and AC-6 (Least Privilege) — see the control section below for these in your framework.

OWASP Top 10 for Web (2025)

A01:2025 Broken Access Control

EU & UK References

Vulnerability Data

Kirby is an open-source content management system. From versions 5.0.0 to 5.2.1, Kirby is missing permission checks in the content changes API. This vulnerability affects all Kirby sites where user permissions are configured to prevent specific role(s) from performing write…

more

actions, specifically by disabling the update permission with the intent to prevent modifications to site content. This vulnerability does not affect those who have not altered the deviated from default user permissions. This issue has been patched in version 5.2.2.

CWE(s)
CWE-863

Related Threats

MITRE ATT&CK Enterprise TechniquesAI

T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
Why these techniques?

Missing permission checks (CWE-863) in the content API directly enable unauthorized write actions, facilitating privilege escalation from restricted roles and exploitation of the public-facing CMS.

Confidence: MEDIUM · MITRE ATT&CK Enterprise v19.0

CVEs Like This One

CVE-2026-40099Same product: Getkirby Kirby
CVE-2026-41325Same product: Getkirby Kirby
CVE-2024-41964Same product: Getkirby Kirby
CVE-2026-42137Same product: Getkirby Kirby
CVE-2026-34587Same product: Getkirby Kirby
CVE-2024-26483Same product: Getkirby Kirby
CVE-2024-26481Same product: Getkirby Kirby
CVE-2026-32870Same product: Getkirby Kirby
CVE-2023-38488Same product: Getkirby Kirby
CVE-2026-42174Same product: Getkirby Kirby

Affected Assets

getkirby
kirby
5.0.0 — 5.2.2

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)
  • AC-3 Access Enforcement
  • AC-6 Least Privilege
  • SI-2 Flaw Remediation
Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)
  • 5 hardening rules · 3 OS baselines
Validate
Prove the fix (OWASP ASVS)

—

Mitigating Controls (NIST 800-53 r5) AI

AC-3 Access Enforcement good match
prevent

Directly enforces the missing update-permission checks on the content changes API that allowed unauthorized write actions.

AC-6 Least Privilege partial match
prevent

Ensures roles are granted only the minimum permissions required, limiting the blast radius when enforcement of the update permission is absent.

SI-2 Flaw Remediation partial match
prevent

Requires prompt application of the vendor patch (5.2.2) that restores the absent authorization checks in the content API.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.AA-05 mostly match
prevents

Defining, enforcing, and reviewing access authorizations and least privilege directly prevents incorrect authorization checks.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.5.15 Access control partial match
prevents

Requiring consistency between access rights and classification plus formal approval steps ensures that the authorization logic correctly distinguishes between entities that should and should not be granted access.

A.5.18 Access rights partial match
prevents

Enforcing policy-driven approval and role-change reviews stops incorrect or stale authorization decisions from remaining in effect after job changes or terminations.

A.8.3 Information access restriction partial match
prevents

By tying access rights to identity, device, location and classification, the control reduces the likelihood that an authorization decision will be based on an incorrect or bypassed policy.

References