Kirby has XML injection in its XML creator toolkit

TL;DR

This vulnerability only affects Kirby sites that use the Xml data handler (e.g. Data::encode($string, 'xml')) or the Xml::create(), Xml::tag() or Xml::value() method(s) in site or plugin code. The Kirby core does not use any of the affected methods.

If consumers use an affected method and cannot rule out input to these methods controlled by an attacker, Kirby strongly recommends that they update to a patch release.

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Introduction

XML strings contain structured data in tags and attributes. Depending on the used XML schema, this data can carry specific meaning that can lead to actions in other systems that parse and act on the XML data. Tags and attributes are detected based on their specific syntax, which includes characters such as <, >, ", and &. If these characters are to be used verbatim in text within the XML string, they can be escaped using a <![CDATA[ ]]> block.

XML injection is an attack on a system generating or parsing XML files. By injecting special characters into input data, XML output with a malicious meaning could be generated by a vulnerable system.

Impact

Kirby's Xml::value() method has special handling for blocks. If the input value is already valid , it is not escaped a second time but allowed to pass through. However it was possible to trick this check into allowing values that only a valid block but also contained other structured data outside of the block. This structured data would then also be allowed to pass through, circumventing the value protection.