Kirby: Cross-site scripting (XSS) from links in KirbyTags and image blocks in the site frontend

Summary

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.

Timeline

1. Jul 16, 2026, 9:49 PM UTCCVE published
2. Jul 18, 2026, 3:18 AM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: partial

3. Jul 18, 2026, 3:18 AM UTCRecord last updated

Affected versions

• getkirby kirby

  fixed in 4.9.1; From 5.0.0 · fixed in 5.4.1

• getkirby/cmsPackagist

  fixed in 4.9.1

• getkirby/cmsPackagist

  From 5.0.0 · fixed in 5.4.1

References 2