ACE vulnerability in conditional configuration file processing by QOS.CH logback-core up to and including version 1.5.18 in Java applications, allows an attacker to execute arbitrary code by compromising an existing logback configuration file or by injecting an environment variable before program execution. A successful attack requires the presence of Janino library and Spring Framework to be present on the user's class path. In addition, the attacker must  have write access to a configuration file. Alternatively, the attacker could inject a malicious environment variable pointing to a malicious configuration file. In both cases, the attack requires existing privilege.