CDATA Section Breakout via Unsanitised ]]> in xml_builder

XML Injection vulnerability in joshnuss xml_builder (XmlBuilder module) allows Content Spoofing, XML Injection.

This vulnerability is associated with program files lib/xml_builder.ex and program routines XmlBuilder.generate/1, XmlBuilder.generate/2, XmlBuilder.escape/1.

The escape/1 clause for {:cdata, data} in lib/xml_builder.ex concatenates data verbatim between the CDATA opener <![CDATA[ and closer ]]> without rewriting or splitting on the embedded ]]> sequence. Because CDATA sections have no internal escape mechanism, the only safe way to embed arbitrary bytes is to split on ]]> and emit adjacent CDATA sections. An attacker who can supply input containing ]]> closes the CDATA section early; any bytes that follow are parsed as ordinary XML markup by downstream consumers, allowing injection of arbitrary elements, text, or entity references into the output document.

This issue affects xml_builder: from 0.0.7 before 2.4.1.