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 Server-Side Request Forgery vulnerability
Server-Side Request Forgery (SSRF) in SaxEventRecorder by QOS.CH logback version 1.5.12 on the Java platform, allows an attacker to forge requests by compromising logback configuration files in XML.
 
The attacks involves the modification of DOCTYPE declaration in  XML configuration files.

QOS.CH logback-core Expression Language Injection vulnerability
ACE vulnerability in JaninoEventEvaluator by QOS.CH logback-core up to and including version 1.5.12 in Java applications allows attackers to execute arbitrary code by compromising an existing logback configuration file or by injecting an environment variable before program execution.

Malicious logback configuration files can allow the attacker to execute arbitrary code using the JaninoEventEvaluator extension.

A successful attack requires the user to 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.