The vulnerability (CWE-611) explicitly describes improper restriction of XML external entity references. Apache XML-RPC's XML parsing logic is the attack surface. Standard XXE vulnerabilities in Java stem from insecure parser configurations (e.g., not disabling DTDs or external entities). While the exact code isn't provided, the library's handling of XML-RPC requests would require XML parsing, and the absence of secure configuration flags (observed in similar vulnerabilities) directly enables this exploit. The high confidence stems from the direct match between the vulnerability type and the library's core functionality.