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Medium

Cross-site scripting (XSS) from writer field content in the site frontend

  • Disclosed: 16.11.2021
  • Updated: 11.10.2026 10:22

Impact

Kirby's writer field stores its formatted content as HTML code. Unlike with other field types, it is not possible to escape HTML special characters against cross-site scripting (XSS) attacks, otherwise the formatting would be lost.

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

Because the writer field did not securely sanitize its contents on save, it was possible to inject malicious HTML code into the content file by sending it to Kirby's API directly without using the Panel. This malicious HTML code would then be displayed on the site frontend and executed in the browsers of site visitors and logged in users who are browsing the site.

This vulnerability is 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.

You are not affected if you don't use the writer field in any of your blueprints. The attack can only be performed by logged-in users and only surfaces in the site frontend (i.e. in your templates). The Panel itself is unaffected and will not execute JavaScript that was injected into writer field content.

Patches

We have patched the vulnerability in Kirby 3.5.8 by sanitizing all writer field contents on the backend whenever the content is modified via Kirby's API. Please update to this or a later version to fix the vulnerability.

Credits

Thanks to Azrul Ikhwan Zulkifli (@azrultech) from BAE Systems AI Vulnerability Research Team for responsibly reporting the identified issue.

Affected software

Click a technology to see all vulnerabilities affecting it.

PlatformPackageVulnerable versionsFixed in
Composer package getkirby/cms >= 3.5.0, < 3.5.8 3.5.8

References

CVSS score 5.4/10
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N
Weakness (CWE)
CWE-79
Platform
Composer
Package
getkirby/cms
Disclosed
16.11.2021
Updated
11.10.2026 10:22

Sources and licenses

OSV / GitHub Advisory Database - GHSA-x7j7-qp7j-hw3q - 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. 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
  17. 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
  18. 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
  19. Cross-site scripting (XSS) from writer field content in the site frontend this entry
    Medium · 5.4 CVE-2021-41252 >= 3.5.0, < 3.5.8 3.5.8
  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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