dom4j before 2.0.3 and 2.1.x before 2.1.3 allows external DTDs and External Entities by default, which might enable XXE attacks. However, there is popular external documentation from OWASP showing how to enable the safe, non-default behavior in any application that uses dom4j.

dom4j version prior to version 2.1.1 contains a CWE-91: XML Injection vulnerability in Class: Element. Methods: addElement, addAttribute that can result in an attacker tampering with XML documents through XML injection. This attack appear to be exploitable via an attacker specifying attributes or elements in the XML document. This vulnerability appears to have been fixed in 2.1.1 or later.

Multiple XML external entity (XXE) vulnerabilities in the (1) Dom4JDriver, (2) DomDriver, (3) JDomDriver, (4) JDom2Driver, (5) SjsxpDriver, (6) StandardStaxDriver, and (7) WstxDriver drivers in XStream before 1.4.9 allow remote attackers to read arbitrary files via a crafted XML document.

The (1) DOMConverter, (2) JDOMConverter, (3) DOM4JConverter, and (4) XOMConverter functions in Direct Web Remoting (DWR) through 2.0.10 and 3.x through 3.0.RC2 allow remote attackers to read arbitrary files via DOM data containing an XML external entity declaration in conjunction with an entity reference, related to an XML External Entity (XXE) issue.