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EUVD-2026-338637

fkie_cve-2026-45368

Kirby is an open-source content management system. In versions prior to 4.9.1 and 5.4.1, the underlying URL methods for the KirbyTags and image blocks components did not filter out malicious URL values that resolve to script execution. The vulnerability affects four first-party Kirby renderers that produce `<a href="…">` output from editor-supplied field values: the (`link: …)` KirbyTag, the `link`: parameter of the `(image: …)` KirbyTag when it does not resolve to a known file or `self`, the `link` field of the built-in image block, and the HTML importer for the `blocks` field (which accepted the same malicious input as the image block `link` field). While simple `avascript:` URLs were already deactivated by treating them as a relative path and prepending a single slash to the URL, the use of URLs of the format `javascript://x%0A…` bypasses this protection. The `vbscript:`, `data:`, `livescript:`, `mocha:` and `jar:` schemes are affected by the same underlying gap. This issue has been fixed in versions 4.9.1 and 5.4.1.

GHSA-qvjf-922g-pj44 — Kirby CMS vulnerable to cross-site scripting (XSS) from links in KirbyTags and image blocks in the site frontend

Affected: Packagist: getkirby/cms

### TL;DR

This vulnerability affects all Kirby sites that allow the use of the `(link: …)` KirbyTag, the `link:` parameter of the `(image: …)` KirbyTag, the built-in `image` block with a link or the HTML importer for blocks, when content is authored by users who may not be fully trusted. The attack requires an authenticated Panel user with update permission to any `textarea` or `blocks` field, or write access to content files through another vector (e.g. a frontend form or content sync pipeline). Another attack vector is the use of `Html::a()` or `Html::link()` with untrusted user input.

**This vulnerability is of high severity for affected sites.**

Kirby sites are *not* affected if none of the mentioned KirbyTags or block types are used, or if every user who can edit content is fully trusted. The attack only surfaces in the site frontend (i.e. in its templates). The Panel itself is unaffected and will not execute JavaScript that was injected into the `textarea` or `blocks` field content.

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### Introduction

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 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.

In a *stored* XSS attack, the malicious payload is saved into the content data and has the potential to affect other users or site visitors.

Such vulnerabilities are critical i…