In version 2.0.3 Apache Santuario XML Security for Java, a caching mechanism was introduced to speed up creating new XML documents using a static pool of DocumentBuilders. However, if some untrusted code can register a malicious implementation with the thread context class loader first, then this implementation might be cached and re-used by Apache Santuario - XML Security for Java, leading to potential security flaws when validating signed documents, etc. The vulnerability affects Apache Santuario - XML Security for Java 2.0.x releases from 2.0.3 and all 2.1.x releases before 2.1.4.