Kirby cross-site scripting (XSS) in the link field "Custom" type

Vulnerability Description

Kirby is a content management system. 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. This vulnerability is patched in 4.1.1.

References

• https://github.com/getkirby/kirby/security/advisories/GHSA-63h4-w25c-3qv4
• https://github.com/getkirby/kirby/commit/cda3dd9a15228d35e62ff86cfa87a67e7c687437