CVE-2018-1285 identifies a critical XML external entity (XXE) vulnerability in Apache log4net before version 2.0.10 that enables attackers to exploit XML parsing weaknesses in configuration file processing. This vulnerability achieves a maximum CVSS score of 9.8 (Critical severity) with an EPSS score of 97.5 percentile and 47.1% exploitation probability, indicating extremely high risk for .NET applications that accept user-controlled log4net configuration files. The vulnerability details reveal that log4net's XML configuration parser fails to disable DTD and external entity processing, allowing attackers to craft malicious configuration files containing XXE payloads that can access local files, perform network requests, or cause denial of service conditions. This creates substantial exploit risk for C# and .NET applications using log4net for logging configuration, particularly affecting enterprise applications that allow dynamic configuration loading, web applications accepting user-supplied logging configurations, and systems that process log4net XML files from untrusted sources without proper validation. The technical root cause lies in log4net's InternalConfigure method within the configuration parsing logic, where XML processing occurs without proper security hardening to prevent external entity resolution, creating a vector for known exploited vulnerabilities targeting XML parsers in .NET applications. The vulnerability specifically affects CWE-611 (XML external entity reference) scenarios where attackers can leverage XXE injection to achieve information disclosure, data modification, or system compromise through malicious DTD declarations and external entity references in log4net configuration files. With major vendors including Oracle and NetApp issuing security advisories due to the widespread adoption of log4net in enterprise .NET environments, this vulnerability demonstrates the critical importance of secure XML parsing practices. Mitigation strategies require upgrading to log4net version 2.0.10 or later, which implements proper XML security controls by disabling external entity processing and DTD resolution during configuration file parsing. Organizations should prioritize identifying all .NET applications using vulnerable log4net versions, implement strict validation for configuration file sources, restrict the ability to supply arbitrary log4net configurations in production environments, and maintain updated CVE database records to track similar XXE vulnerabilities that could compromise application security through unsafe XML processing and configuration manipulation attacks in logging frameworks.