A zero-day exploit was recently identified within the Apache log4j logging library, which can potentially be used by hackers to take over entire servers via logging messages. The vulnerability affects a number of online services, from Steam and Twitter to Amazon and Minecraft, among others.
https://www.notebookcheck.net/Apache-Log4j-zero-day-exploit-could-be-used-by-hackers-to-target-users-on-Steam-Twitter-Amazon-and-other-platforms.584531.0.html