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Kirby CMS has Persistent DoS via Malformed Image Upload

Moderate severity GitHub Reviewed Published Mar 26, 2026 in Stalin-143/CVE-2026-29905 • Updated Mar 27, 2026

Package

composer getkirby/cms (Composer)

Affected versions

< 5.2.0-rc.1

Patched versions

5.2.0-rc.1

Description

Summary

Kirby CMS through version 5.1.4 allows an authenticated user with Editor permissions to cause a persistent Denial of Service (DoS) via a malformed image upload.

Details

The vulnerability is caused by improper validation of the return value of PHP's getimagesize() function. When a malformed file is uploaded with a valid image extension (e.g., .jpg), the function returns false instead of an expected array.

The application fails to handle this condition properly and proceeds with image processing, resulting in a fatal TypeError. This leads to persistent application crashes when the affected file is accessed.

Impact

  • Persistent Denial of Service (DoS)
  • Affected pages return HTTP 500 errors
  • Requires manual removal of the malformed file to restore functionality
  • Exploitable by authenticated users with Editor permissions

References

@Stalin-143 Stalin-143 published to Stalin-143/CVE-2026-29905 Mar 26, 2026
Published by the National Vulnerability Database Mar 26, 2026
Published to the GitHub Advisory Database Mar 27, 2026
Reviewed Mar 27, 2026
Last updated Mar 27, 2026

Severity

Moderate

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
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

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:L/PR:L/UI:N/S:U/C:N/I:N/A:H

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.
(10th percentile)

Weaknesses

Improper Input Validation

The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly. Learn more on MITRE.

CVE ID

CVE-2026-29905

GHSA ID

GHSA-cw7v-45wm-mcf2

Source code

Credits

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