Executive brief
The xml_builder library is an Elixir package used to programmatically generate XML documents. A flaw in how it handles CDATA sections allows attackers to inject arbitrary XML markup by embedding the CDATA terminator sequence into input data. This could enable attackers to inject malicious XML elements, attributes, or external entity references into generated documents, potentially leading to data corruption, information disclosure, or further attacks on systems consuming the XML output.
Technical details
The vulnerability is an XML injection flaw in the escape/1 function (specifically the {:cdata, data} clause) within lib/xml_builder.ex. The vulnerable code concatenates user-supplied data directly between CDATA markers <![CDATA[ and ]]> without splitting or escaping the CDATA terminator sequence ]]>. An attacker who controls input to XmlBuilder.generate/1 or XmlBuilder.generate/2 can embed ]]> to prematurely close the CDATA section, allowing injection of arbitrary XML markup that will be parsed as valid XML by downstream consumers. The attack requires the ability to supply input to the affected functions; no authentication or special preconditions are documented. The fix is available in version 2.4.1 and later; versions 0.0.7 through 2.4.0 are affected.
Affected products
- joshnuss xml_builder 0.0.7 before 2.4.1
Timeline
- 2026-08-21: disclosed