Extensible Stylesheet Language Transformations (XSLT) is a transformation language that ingests an XML document and transforms that document into another XML document. If an attacker can control the content of the style sheet, he/she would potentially be able to trigger remote code execution (RCE) or server-side path traversal.
Fixes for JSP XSLT
Take for example a simple XSLT transform,
<?xml version="1.0" encoding="utf-8"?> <xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"> <xsl:template match="/technology_companies"> <xsl:value-of select="system-property('xsl:vendor')"/> </xsl:template> </xsl:stylesheet>
In this example the logic injects value matching
/technology_companies, this could be a potential area to inject code. If an attacker were to be able to inject directives, they could discover the XSLT library being used and exploit further, e.g.
A general solution if XSLT is required to be used:
- Avoid interpreting user defined XSLT documents
- Do not generate XSLT documents and internal fields from inputs that can be controlled by the user, e.g. company name
- Based upon the XSLT library in use, review the library’s default settings and disable unsafe functionality that could lead to XML External Entities from being executed