Package Instance

Logback allows an attacker to instantiate classes already present on the class path
ACE vulnerability in configuration file processing  by QOS.CH logback-core up to and including version 1.5.24 in Java applications, allows an attacker to instantiate classes already present on the class path by compromising an existing logback configuration file.

The instantiation of a potentially malicious Java class requires that said class is present on the user's class-path. In addition, the attacker must  have write access to a configuration file. However, after successful instantiation, the instance is very likely to be discarded with no further ado.

QOS.CH logback-core is vulnerable to Arbitrary Code Execution through file processing
QOS.CH logback-core versions up to 1.5.18 contain an ACE vulnerability in conditional configuration file processing in Java applications. This vulnerability allows an attacker to execute arbitrary code by compromising an existing logback configuration file or by injecting a malicious environment variable before program execution.

A successful attack requires the Janino library and Spring Framework to be present on the user's class path. Additionally, 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 privileges.