In Apache Log4j, there is a Remote Code Injection vulnerability aka Log4Shell.
A critical vulnerability has been discovered in Apache Log4j 2, an open-source Java package used to enable logging in many popular applications, and it can be exploited to enable remote code execution on countless servers.
Millions of applications use Log4j for logging, and all the attacker needs to do is get the app to log a special string. So far iCloud, Steam, and Minecraft have all been confirmed vulnerable.
Simply changing an iPhone's name has been shown to trigger the vulnerability in Apple's servers.
Apache Log4j2 2.0-beta9 through 2.12.1 and 2.13.0 through 2.15.0 JNDI features used in configuration, log messages, and parameters do not protect against attacker controlled LDAP and other JNDI related endpoints. An attacker who can control log messages or log message parameters can execute arbitrary code loaded from LDAP servers when message lookup substitution is enabled. From log4j 2.15.0, this behavior has been disabled by default. From version 2.16.0, this functionality has been completely removed. Note that this vulnerability is specific to log4j-core and does not affect log4net, log4cxx, or other Apache Logging Services projects.
Download the latest Log4j mitigated version from its download page and upgrade to the newest version.
The following mitigations are also recommended: