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Medium

Kirby vulnerable to Cross-site scripting (XSS) in the link field "Custom" type

  • Disclosed: 26.02.2024
  • Updated: 11.10.2026 10:22

TL;DR

This vulnerability affects Kirby sites that use the new link field and output the entered link without additional validation or sanitization.

The attack commonly requires user interaction by another user or visitor.

The link dialog of the writer field is not affected as the writer field content is automatically sanitized by the Kirby backend code. You are also already protected if you limit the acceptable link types with the options field property.

Introduction

Cross-site scripting (XSS) is a type of vulnerability that allows to execute any kind of JavaScript code inside the Panel session of the same or other users. In the Panel, a harmful script can for example trigger requests to Kirby's API with the permissions of the victim.

Such vulnerabilities are critical if you might have potential attackers in your group of authenticated Panel users. They can escalate their privileges if they get access to the Panel session of an admin user. Depending on your site, other JavaScript-powered attacks are possible.

Impact

The new link field introduced in Kirby 4 allows several different link types that each validate the entered link to the relevant URL format. It also includes a "Custom" link type for advanced use cases that don't fit any of the pre-defined link formats.

As the "Custom" link type is meant to be flexible, it also allows the javascript: URL scheme. In some use cases this can be intended, but it can also be misused by attackers to execute arbitrary JavaScript code when a user or visitor clicks on a link that is generated from the contents of the link field.

Patches

The problem has been patched in Kirby 4.1.1. Please update to this or a later version to fix the vulnerability.

In the patch release, we have updated the link field to hide the "Custom" link type by default and added a warning to our documentation that this link type should only be enabled if additional validation is performed or no protection against XSS attacks is needed.

Credits

Thanks to Natwara Archeepsamooth (@PlyNatwara) for responsibly informing us about the javascript: attack vector.

Affected software

Click a technology to see all vulnerabilities affecting it.

PlatformPackageVulnerable versionsFixed in
Composer package getkirby/cms >= 4.0.0, < 4.1.1 4.1.1

References

CVSS score 4.6/10
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N
Weakness (CWE)
CWE-79
Platform
Composer
Package
getkirby/cms
Disclosed
26.02.2024
Updated
11.10.2026 10:22

Sources and licenses

OSV / GitHub Advisory Database - GHSA-63h4-w25c-3qv4 - CC BY 4.0

Vulnerability history: getkirby/cms

All published vulnerabilities of this package (Composer package), newest first. Shows whether this is a one-off slip or a package that needs watching.

All (51) in the archive
Total entries
51
First → latest
12.2020 09.2026
Without a fix
2
Exploited in attacks
0

Severity breakdown

  • Critical 1
  • High 19
  • Medium 30
  • Low 1

Disclosures per year

Severity:
  1. Kirby: File upload permissions are not checked during processing of chunk data
    High CVE-2026-71415 >= 5.0.0, < 5.5.2 5.5.2
  2. Kirby: Access to image files and limited access to JSON files outside of the site root via path traversal in the media handling
    High CVE-2026-75594 < 4.9.5, >= 5.0.0, < 5.5.2 4.9.5, 5.5.2
  3. Kirby: `pages.access` permission is not checked in the `site/find` REST API route
    High CVE-2026-54005 < 4.9.4, >= 5.0.0-alpha.1, < 5.4.4 4.9.4, 5.4.4
  4. Kirby: External Initialization of the Panel on reverse proxy setups with the `Forwarded` header
    Critical CVE-2026-54003 < 4.9.4, >= 5.0.0-alpha.1, < 5.4.4 4.9.4, 5.4.4
  5. Kirby: Cross-site scripting (XSS) from incomplete HTML/XML sanitization in `Dom::sanitize()`
    High CVE-2026-54002 < 4.9.4, >= 5.0.0-alpha.1, < 5.4.4 4.9.4, 5.4.4
  6. Kirby: Self cross-site scripting (self-XSS) in the writer field
    High CVE-2026-49276 < 4.9.4, >= 5.0.0-alpha.1, < 5.4.4 4.9.4, 5.4.4
  7. Kirby CMS vulnerable to cross-site scripting (XSS) from links in KirbyTags and image blocks in the site frontend
    High CVE-2026-45368 < 4.9.1, >= 5.0.0, < 5.4.1 4.9.1, 5.4.1
  8. Kirby CMS has pre-authentication path traversal and PHP file inclusion during user lookup
    High CVE-2026-44177 >= 5.3.0, < 5.4.1 5.4.1
  9. Kirby CMS vulnerable to cross-site scripting (XSS) from list field content in the site frontend
    High CVE-2026-44175 < 4.9.1, >= 5.0.0, < 5.4.1 4.9.1, 5.4.1
  10. Kirby CMS has an Arbitrary Method Call via REST API Search and Collection Query Endpoints
    High CVE-2026-44174 < 4.9.1, >= 5.0.0, < 5.4.1 4.9.1, 5.4.1
  11. Kirby CMS's read access to site, user and role information is not gated by permissions
    High CVE-2026-42069 < 4.9.0, >= 5.0.0, < 5.4.0 4.9.0, 5.4.0
  12. Kirby CMS's `pages.access/list` and `files.access/list` permissions are not consistently checked in the Panel and REST API
    High CVE-2026-42137 < 4.9.0, >= 5.0.0, < 5.4.0 4.9.0, 5.4.0
  13. Kirby is vulnerable to authorization bypass during page, file and user creation via blueprint injection
    High CVE-2026-41325 < 4.9.0, >= 5.0.0, < 5.4.0 4.9.0, 5.4.0
  14. Kirby has Server-Side Template Injection (SSTI) via double template resolution in option rendering
    High · 8.1 CVE-2026-34587 < 4.9.0, >= 5.0.0, < 5.4.0 4.9.0, 5.4.0
  15. Kirby has insufficient permission checks in the language settings
    High · 8.1 CVE-2024-41964 < 3.6.6.6, >= 3.7.0, < 3.7.5.5, >= 3.8.0, < 3.8.4.4, >= 3.9.0, < 3.9.8.2, >= 3.10.0, < 3.10.1.1, >= 4.0.0, < 4.3.1 3.6.6.6, 3.7.5.5, 3.8.4.4, 3.9.8.2, 3.10.1.1, 4.3.1
  16. Kirby vulnerable to Cross-site scripting (XSS) in the link field "Custom" type this entry
    Medium · 4.6 CVE-2024-27087 >= 4.0.0, < 4.1.1 4.1.1
  17. Field injection in the KirbyData text storage handler
    High · 7.1 CVE-2023-38488 < 3.5.8.3, >= 3.6.0, < 3.6.6.3, >= 3.7.0, < 3.7.5.2, >= 3.8.0, < 3.8.4.1, >= 3.9.0, < 3.9.6 3.5.8.3, 3.6.6.3, 3.7.5.2, 3.8.4.1, 3.9.6
  18. Insufficient Session Expiration after a password change
    High · 7.3 CVE-2023-38489 < 3.5.8.3, >= 3.6.0, < 3.6.6.3, >= 3.7.0, < 3.7.5.2, >= 3.8.0, < 3.8.4.1, >= 3.9.0, < 3.9.6 3.5.8.3, 3.6.6.3, 3.7.5.2, 3.8.4.1, 3.9.6
  19. Cross-site scripting from content entered in the tags and multiselect fields
    High · 7.1 ghsa-rv3r-vqjj-8c76 >= 3.5.7, < 3.5.8.1, >= 3.6.0, < 3.6.6.1, >= 3.7.0, < 3.7.4 3.5.8.1, 3.6.6.1, 3.7.4
  20. Cross-site scripting (XSS) from field and configuration text displayed in the Panel
    High · 7.1 CVE-2021-32735 < 3.5.7 3.5.7
  21. Cross-site scripting (XSS) from unsanitized uploaded SVG files in Kirby
    High · 7.6 CVE-2021-29460 < 3.5.4 3.5.4

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